SERVICE ORIENTED ARCHITECTURE

SOA

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Enlaces interesantes: - Wikipedia, buscar SOA, pero en inglés - http://arquitecturaorientadaaservicios.blogspot.com/ - www.microsoft.com/soa

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1 http://en.wikipedia.org/wiki/Service-oriented_architecture

In computing, service-oriented architecture (SOA) provides methods for systems development and integration where systems group functionality around business processes and package these as interoperable services. A SOA infrastructure allows different applications to exchange data with one another as they participate in business processes. Service-orientation aims at a loose coupling of services with operating systems, programming languages and other technologies that underlie applications[1]. SOA separates functions into distinct units, or services[2], which developers make accessible over a network in order that users can combine and reuse them in the production of business applications[3]. These services communicate with each other by passing data from one service to another, or by coordinating an activity between two or more services. Many commentators[who?] see SOA concepts as built upon and evolving from older concepts of distributed computing[3][2] and modular programming.

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1.1 Contents

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1 Description o 1.1 Overview o 1.2 Introduction o 1.3 Requirements o 1.4 Principles o 1.5 Web services approach o 1.6 SOA and Web service protocols o 1.7 Other SOA concepts o 1.8 SOA definitions o 1.9 Service contract o 1.10 SOA and business architecture o 1.11 SOA and network management architecture

2 Discussion o 2.1 Benefits o 2.2 Challenges in adopting SOA o 2.3 Criticisms of SOA

3 Extensions o 3.1 SOA, Web 2.0, and mashups o 3.2 Web 2.0

4 See also 5 References

1.2 [edit] Description

1.2.1 [edit] Overview

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A SOA.

Companies have long sought to integrate existing systems in order to implement information technology (IT) support for business processes that cover all present and prospective systems requirements needed to run the business end-to-end. A variety of designs serve this end, ranging from rigid point-to-point electronic data interchange (EDI) interactions to web auctions. By updating older technologies, for example by Internet-enabling EDI-based systems, companies can make their IT systems available to internal or external customers; but the resulting systems have not proven flexible enough to meet business demands that require a flexible, standardized architecture to better support the connection of various applications and the sharing of data.

SOA offers one such prospective architecture. It unifies business processes by structuring large applications as an ad hoc collection of smaller modules called "services". Different groups of people both inside and outside an organization can use these applications, and new applications built from a mix of services from the global pool exhibit greater flexibility and uniformity. One should not, for example, have to provide redundantly the same personal information to open an online checking, savings or IRA account, and further, the interfaces one interacts with should have the same look and feel and use the same level and type of input-data validation. Building all applications from the same pool of services makes achieving this goal much easier and more deployable to affiliated companies. For example: interacting with a rental-car company's reservation system from an airline's reservation system.

Service Oriented Architecture (SOA) provides a design framework with a view to realizing rapid and low-cost system development and to improving total system-quality. SOA may use web services standards and web technologies and is rapidly becoming a standard approach for enterprise information systems.

Web services face significant challenges because of particular requirements. Applying the SOA paradigm to a real-time system presents many problems, including response time, support of event-driven, asynchronous parallel applications, complicated human

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interface support, reliability, etc. This article defines SOA and includes detailed discussion on several issues that arise when applying SOA to industrial systems.

1.2.2 [edit] Introduction

One can define a service-oriented architecture (SOA) as a group of services that communicate with each other. The process of communication involves either simple data-passing or two or more services coordinating some activity. Intercommunication implies the need for some means of connecting two or more services to each other.

SOAs build applications out of software services. Services comprise intrinsically unassociated units of functionality that have no calls to each other embedded in them. They typically implement functionality most humans would recognize as a service, such as filling out an online application for an account, viewing an online bank-statement, or placing an online booking or airline ticket order. Instead of services embedding calls to each other in their source code, they use defined protocols that describe how one or more services can "talk" to each other. This architecture then relies on a business process expert to link and sequence services, in a process known as orchestration, to meet a new or existing business system requirement.

Relative to typical practices of earlier attempts to promote software reuse via modularity of functions or by use of predefined groups of functions known as classes, SOA's atomic-level objects often end up 100 to 1,000 times larger.[citation needed]

A software developer or software engineer associates individual SOA objects by using orchestration. In the process of orchestration, a software engineer or process engineer associates relatively large chunks of software functionality (services) in a non-hierarchical arrangement (in contrast to a class hierarchy) by using a special software tool that contains an exhaustive list of all of the services, their characteristics, and a means to record the designer's choices that the designer can manage and the software system can consume and use at run-time.

Underlying and enabling all of this requires metadata in sufficient detail to describe not only the characteristics of these services, but also the data that drives them. Programmers have made extensive use of XML in SOA to structure data that they wrap in a nearly exhaustive description-container. Analogously, WSDL typically describe the services themselves, while SOAP describes the communications protocols. Whether these description languages are the best possible for the job, and whether they will remain the favorites in the future, remains an open question. In the meantime SOA depends on data and services that are described using some implementation of metadata that meets the following two criteria:

1. the metadata must come in a form that software systems can use to configure dynamically by discovery and incorporation of defined services, and also to maintain coherence and integrity

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2. the metadata must also come in a form that system designers can understand and manage with a reasonable expenditure of cost and effort

SOA has the goal of allowing users to string together fairly large chunks of functionality to form ad hoc applications that are built almost entirely from existing software services. The larger the chunks, the fewer the interface points required to implement any given set of functionality; however, very large chunks of functionality may not prove sufficiently granular for easy reuse. Each interface brings with it some amount of processing overhead, so there is a performance consideration in choosing the granularity of services. The great promise of SOA suggests that the marginal cost of creating the n-th application is low, as all of the software required already exists to satisfy the requirements of other applications. Ideally, one requires only orchestration to produce a new application.

For this to operate, no interactions must exist between the chunks specified or within the chunks themselves. Instead, the interaction of services (all of them unassociated peers) is specified by humans in a relatively ad hoc way with the intent driven by newly emergent business requirements. Thus the need for services as much larger units of functionality than traditional functions or classes, lest the sheer complexity of thousands of such granular objects overwhelm the application designer. Programmers develop the services themselves using traditional languages like Java, C#, C, C++ or COBOL.

SOA services feature loose coupling, in contrast to the functions that a linker binds together to form an executable, to a dynamically linked library or to an assembly. SOA services also run in "safe" wrappers such as Java or .NET, and other programming languages that manage memory allocation and reclamation, allow ad hoc and late binding, and provide some degree of indeterminate data typing.

As of 2008, increasing numbers of third-party software companies offer software services for a fee. In the future, SOA systems may consist of such third-party services combined with others created in-house. This has the potential to spread costs over many customers and customer uses, and promotes standardization both in and across industries. In particular, the travel industry now has a well-defined and documented set of both services and data, sufficient to allow any reasonably competent software engineer to create travel-agency software using entirely off-the-shelf software services. Other industries, such as the finance industry, have also started making significant progress in this direction.

SOA as an architecture relies on service-orientation as its fundamental design principle[4]. In a SOA environment, users can access independent services without knowledge of their underlying platform implementation[5].

SOA relies on services exposing their functionality via interfaces that other applications and services can read to understand how to utilize those services.

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1.2.3 [edit] Requirements

In order to efficiently use a SOA, one must[citation needed] meet the following requirements:

Interoperability between different systems and programming languages provides the basis for integration between applications on different platforms through a communication protocol. One example of such communication is based on the concept of messages. Using messages across defined message channels decreases the complexity of the end application, thereby allowing the developer of the application to focus on true application functionality instead of the intricate needs of a communication protocol.

Desire to create a federation of resources. Establish and maintain data flow to a federated data warehouse. This allows new functionality developed to reference a common business format for each data element.

1.2.4 [edit] Principles

The following guiding principles define the ground rules for development, maintenance, and usage of the SOA[6]:

Reuse, granularity, modularity, composability, componentization, portability, and interoperability

Standards compliance (both common and industry-specific) Services identification and categorization, provisioning and delivery, and

monitoring and tracking

The following specific architectural principles for design and service definition focus on specific themes that influence the intrinsic behaviour of a system and the style of its design:

Service encapsulation – Many web services are consolidated to be used under the SOA. Often such services were not planned to be under SOA.

Service loose coupling – Services maintain a relationship that minimizes dependencies and only requires that they maintain an awareness of each other

Service contract – Services adhere to a communications agreement, as defined collectively by one or more service description documents

Service abstraction – Beyond what is described in the service contract, services hide logic from the outside world

Service reusability – Logic is divided into services with the intention of promoting reuse

Service composability – Collections of services can be coordinated and assembled to form composite services

Service autonomy – Services have control over the logic they encapsulate

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Service optimization – All else equal, high-quality services are generally considered preferable to low-quality ones

Service discoverability – Services are designed to be outwardly descriptive so that they can be found and assessed via available discovery mechanisms[7]

Service Relevance – Functionality is presented at a granularity recognized by the user as a meaningful service

The following references provide additional considerations for defining a SOA implementation:

SOA Reference Architecture provides a working design of an enterprise-wide SOA implementation with detailed architecture diagrams, component descriptions, detailed requirements, design patterns, opinions about standards, patterns on regulation compliance, standards templates etc.[8]

Life cycle management SOA Practitioners Guide Part 3: Introduction to Services Lifecycle introduces the Services Lifecycle and provides a detailed process for services management though the service lifecycle, from inception to retirement or repurposing of the services. It also contains an appendix that includes organization and governance best practices, templates, comments on key SOA standards, and recommended links for more information.

In addition, one might take the following factors into account when defining a SOA implementation:

efficient use of system resources service maturity and performance EAI Enterprise Application Integration

1.2.5 [edit] Web services approach

Web services can implement a service-oriented architecture. Web services make functional building-blocks accessible over standard Internet protocols independent of platforms and programming languages. These services can be new applications or just wrapped around existing legacy systems to make them network-enabled.

Each SOA building block can play one or both of two roles:

1. Service provider The service provider creates a Web service and possibly publishes its interface and access information to the service registry. Each provider must decide which services to expose, how to make trade-offs between security and easy availability, how to price the services, or (if no charges apply) how to exploit them for other value. The provider also has to decide what category the service should be listed in for a given broker service and what sort of trading partner agreements are required to use the service. It registers what services are

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available within it, and lists all the potential service recipients. The implementer of the broker then decides the scope of the broker. Public brokers are available through the Internet, while private brokers are only accessible to a limited audience, for example, users of a company intranet. Furthermore, the amount of the offered information has to be decided. Some brokers specialize in many listings. Others offer high levels of trust in the listed services. Some cover a broad landscape of services and others focus within an industry. There are also brokers that catalog other brokers. Depending on the business model, brokers can attempt to maximize look-up requests, number of listings or accuracy of the listings. The Universal Description Discovery and Integration (UDDI) specification defines a way to publish and discover information about Web services. Other service broker technologies include for example ebXML (Electronic Business using eXtensible Markup Language) and those based on the ISO/IEC 11179 Metadata Registry (MDR) standard.

2. Service requester The service requester or Web service client locates entries in the broker registry using various find operations and then binds to the service provider in order to invoke one of its Web services. Which service the service-requesters need, they have to take it into the Brokers, then bind it with respective service and then use it. They can access multiple services, if the service provide multiple services.

1.2.6 [edit] SOA and Web service protocols

This section does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. (June 2006)

Implementors commonly build SOAs using Web services standards (for example, using SOAP) that have gained[when?] broad industry acceptance. These standards (also referred to as Web Service specifications) also provide greater interoperability and some protection from lock-in to proprietary vendor software. One can, however, implement SOA using any service-based technology, such as Jini, CORBA or REST.

1.2.7 [edit] Other SOA concepts

Architectures can operate independently of specific technologies[3]. Designers can implement SOA using a wide range of technologies, including SOAP, REST, RPC, DCOM, CORBA, Web Services or WCF (Microsoft's implementation of Webservice forms a part of WCF). SOA can be implemented using one or more of these protocols and, for example, might use a file-system mechanism to communicate data conforming to a defined interface-specification between processes conforming to the SOA concept. The key is independent services with defined interfaces that can be called to perform their tasks in a standard way, without a service having foreknowledge of the calling

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application, and without the application having or needing knowledge of how the service actually performs its tasks.

Elements of SOA, by Dirk Krafzig, Karl Banke, and Dirk Slama. Enterprise SOA. Prentice Hall, 2005

SOA Meta Model, The Linthicum Group, 2007

Service-Oriented Modeling Framework (SOMF) Version 2.0

One can also regard SOA as a style of information systems architecture that enables the creation of applications that are built by combining loosely coupled and interoperable services[9]. These services inter-operate based on a formal definition (or contract, e. g., WSDL) that is independent of the underlying platform and programming language. The interface definition hides the implementation of the language-specific service. SOA-based systems can therefore function independently of development technologies and platforms (such as Java, .NET etc). Services written in C# running on .NET platforms and services written in Java running on Java EE platforms, for example, can both be consumed by a common composite application (or client). Applications running on either platform can also consume services running on the other as Web services that facilitates reuse. Managed environments can also wrap COBOL legacy systems and present them as software services. This has extended the useful life of many core legacy systems indefinitely, no matter what language they originally used.

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SOA can support integration and consolidation activities within complex enterprise systems, but SOA does not specify or provide a methodology or framework for documenting capabilities or services.

High-level languages such as BPEL and specifications such as WS-CDL and WS-Coordination extend the service concept by providing a method of defining and supporting orchestration of fine-grained services into more coarse-grained business services, which architects can in turn incorporate into workflows and business processes implemented in composite applications or portals[citation needed].

The use of Service Component Architecture (SCA) to implement SOA is a current area of research.

How can a SOA address interoperability and reusability challenges of computing environments and simplify the heterogeneous business and technological landscapes built over decades? SOA introduces another concept to help practitioners to understand their complex environments by modeling practices. These disciplines are introduced by the service-oriented modeling paradigm[2], a SOA framework that identifies the various disciplines that guide SOA practitioners to conceptualize, analyze, design, and architect their service-oriented assets. Thus, the Service-Oriented Modeling Framework (SOMF) is a work structure, a "map" depicting the various components that contribute to a successful service-oriented modeling approach. It illustrates the major elements that identify the “what to do” aspects of a service development scheme. These modeling pillars enable practitioners to craft an effective project plan and to identify the milestones of a service-oriented initiative — either a small project, a large-scale business, or a technological venture. SOMF also provides a common language, a modeling notation to address one of the major intrinsic collaboration requirements of our times: alignment between business and IT organizations. This crucial vocabulary, if employed, can also illustrate the following SOA principles:

Business Traceability Architectural Best-Practices Traceability Technological Traceability SOA Value Proposition Software Assets Reuse SOA Integration Strategies Technological Abstraction and Generalization Architectural Components Abstraction

"Service-Oriented Modeling Framework (SOMF) Example". http://www.modelingconcepts.com/pdf/SOMF_ANALYSIS_MODELING.pdf.

"Download SOMF Examples & Language Notation". http://www.modelingconcepts.com/pages/download.htm.

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1.2.8 [edit] SOA definitions

SOA is a design for linking computational resources (principally applications and data) on demand to achieve the desired results for service consumers (either end users or other services). OASIS (the Organization for the Advancement of Structured Information Standards) defines SOA as the following:

A paradigm for organizing and utilizing distributed capabilities that may be under the control of different ownership domains. It provides a uniform means to offer, discover, interact with and use capabilities to produce desired effects consistent with measurable preconditions and expectations.

There are multiple definitions of SOA, the OASIS group and the Open Group have created formal definitions with depth that can be applied to both the technology and business domains.

Open Group SOA Definition (SOA-Definition)[10] OASIS SOA Reference Model (SOA-RM)[11]

In addition, SOA is an approach to architecture, whereby business services are the key organizing principles that drive the design of IT to be aligned with business needs.

1.2.9 [edit] Service contract

A service contract needs[citation needed] to have the following components:

Header o Name – Name of the service. Should indicate in general terms what it

does, but not be the only definition o Version – The version of this service contract o Owner – The person/team in charge of the service o RACI

Responsible – The role/person/team responsible for the deliverables of this contract/service. All versions of the contract

Accountable – Ultimate Decision Maker in terms of this contract/service

Consulted – Who must be consulted before action is taken on this contract/service. This is two-way communication. These people have an impact on the decision or the execution of that decision.

Informed – Who must be informed that a decision or action is being taken. This is a one-way communication. These people are impacted by the decision or execution of that decision, but have no control over the action.

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o Type – This is the type of the service to help distinguish the layer in which it resides. Different implementations will have different service types. Examples of service types include:

Presentation Process Business Data Integration

Functional o Functional Requirement (from Requirements Document) – Indicates the

functionality in specific bulleted items what exactly this service accomplishes. The language should be such that it allows test cases to prove the functionality is accomplished.

o Service Operations – Methods, actions etc. Must be defined in terms of what part of the functionality it provides.

o Invocation – Indicates the invocation means of the service. This includes the URL, interface, etc. There may be multiple invocation paths for the same service. We may have the same functionality for an internal and some external clients, each with different invocation means and interfaces. Examples:

SOAP REST Events Triggers

Non-Functional o Security Constraints – Defines who can execute this service in terms of

roles or individual partners etc. and which invocation mechanism they can invoke.

o Quality of Service – Determines the allowable failure rate o Transactional – Is this capable of acting as part of a larger transaction

and if so, how do we control that? o Service Level Agreement – Determines the amount of latency the

service is allowed to have to perform its actions o Semantics – Dictates or defines the meaning of terms used in the

description and interfaces of the service o Process – Describes the process, if any, of the contracted service

1.2.10 [edit] SOA and business architecture

SOA has gained ground as a mechanism for defining business services[12] and operating models (e. g., Business-Agile Enterprise) and thus provide a structure for IT to deliver against the actual business requirements and adapt in a similar way to the business. The purpose of using SOA as a business mapping tool is to ensure that the services created properly represent the business view and are not just what technologists think the business services should be. At the heart of SOA planning is the process of defining architectures for the use of information in support of the business, and the plan for

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implementing those architectures[13]. Enterprise Business Architecture should always represent the highest and most dominant architecture. Every service should be created with the intent to bring value to the business in some way and must be traceable back to the business architecture.

Within this area, IBM announced SOMA (service-oriented modeling and architecture[14]) as the first publicly announced SOA-related methodology in 2004. Since then, efforts have been made to move towards greater standardization and the involvement of business objectives, particularly within the OASIS standards group and specifically the SOA Adoption Blueprints group. All of these approaches take a fundamentally structured approach to SOA, focusing more on the Services and Architecture elements and leaving implementation to the more technically focused standards. Another pertinent example is SAP Enterprise Services Architecture, which is focused on a strict governance process and the use of semantics to improve the usefulness of services in business process innovation.

1.2.11 [edit] SOA and network management architecture

The principles of SOA are currently being applied to the field of network management. Examples of service-oriented network management architectures are TS 188 001 NGN Management OSS Architecture from ETSI, and M.3060 Principles for the Management Of Next Generation Networks recommendation from the ITU-T.

Tools for managing SOA infrastructure include:

HP Management Software / Mercury SOA Manager HyPerformix IPS Performance Optimizer IBM Tivoli Framework

1.3 [edit] Discussion

1.3.1 [edit] Benefits

Enterprise architects believe that SOA can help businesses respond more quickly and cost-effectively to changing market conditions[15]. This style of architecture promotes reuse at the macro (service) level rather than micro (classes) level. It can also simplify interconnection to – and usage of – existing IT (legacy) assets.

In some respects, one can regard SOA as an architectural evolution rather than as a revolution. It captures many of the best practices of previous software architectures. In communications systems, for example, little development has taken place of solutions that use truly static bindings to talk to other equipment in the network. By

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formally embracing a SOA approach, such systems are better positioned to stress the importance of well-defined, highly inter-operable interfaces[16].

Some[who?] have questioned whether SOA is just a revival of modular programming (1970s), event-oriented design (1980s) or interface/component-based design (1990s)[citation needed]. SOA promotes the goal of separating users (consumers) from the service implementations. Services can therefore be run on various distributed platforms and be accessed across networks. This can also maximize reuse of services[citation needed].

SOA is an architectural and design discipline conceived to achieve the goals of increased interoperability (information exchange, reusability, and composability), increased federation (uniting resources and applications while maintaining their individual autonomy and self-governance), and increased business and technology domain alignment.

Service-Oriented Architecture (SOA) is an architectural approach (or style) for constructing complex software-intensive systems from a set of universally interconnected and interdependent building blocks, called services.

SOA realizes its business and IT benefits through utilizing an analysis and design methodology when creating services that ensures they are consistent with the architectural vision and roadmap, and adhere to principles of service-orientation. Arguments supporting the business and management aspects from SOA are outlined in various publications[17].

A service comprises a stand-alone unit of functionality available only via a formally defined interface. Services can be some kind of "nano-enterprises" that are easy to produce and improve. Also services can be "mega-corporations" that are constructed as coordinated work of sub-ordinate services.

Services generally adhere to the following principles of service-orientation:

abstraction autonomy composability discoverability formal contract loose coupling reusability statelessness

A mature rollout of SOA effectively defines the API of the organization.

Implementation of services should be treated as separate projects from the larger project for three reasons:

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It promotes the concept to the business that services can be delivered quickly and independently from the larger and slower-moving projects common in the organization. The business starts understanding systems and simplified user interfaces calling on services. This advocates agility.

It promotes the decoupling of services from its consuming project. This encourages good design where the service is designed without knowing who its consumers are.

Documentation and test artifacts of the service are not embedded within the detail of the larger project. This is important when the service needs to be reused later.

An indirect benefit of SOA is dramatically simplified testing. Services are autonomous, stateless, with fully documented interfaces, and separate from the cross-cutting concerns of the implementation. The industry has never been exposed to this circumstance before.

If appropriate test data is defined in the organization, then when a service is being built, a corresponding stub is built that reacts to the test data. A full set of regression tests, scripts, data, and responses is also captured for the service. The service can be tested as a 'black box' using existing stubs corresponding to the services it calls. Test environments can be constructed where the primitive and out-of-scope services are stubs, while the remainder of the mesh are test deployments of full services. As each interface is fully documented, with its own full set of regression test documentation, it becomes simple to identify problems in test services. Testing evolves to merely validating that the test service operates according to its documentation, and in finding gaps in documentation and test cases of all services within the environment. Managing data state of idempotent services is the only complexity.

Examples may prove useful to aid in documenting a service to the level where it becomes useful. The documentation of some API's within the Java Community Process are good examples. As these are exhaustive, staff would typically use only important subsets. The 'ossjsa.pdf' file within JSR-89 is an example for such a file. JSR-89 Spec Dowmload

1.3.2 [edit] Challenges in adopting SOA

One obvious and common challenge faced involves managing services metadata[citation

needed]. SOA-based environments can include many services that exchange messages to perform tasks. Depending on the design, a single application may generate millions of messages. Managing and providing information on how services interact is a complicated task. This becomes even more complicated when these services are delivered by different organizations within the company or even different companies (partners, suppliers, etc). This creates huge trust issues across teams, and hence SOA Governance comes into picture.

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Another challenge involves the lack of testing in SOA space. There are no sophisticated tools that provide testability of all headless services (including message and database services along with web services) in a typical architecture. Lack of horizontal trust requires that both producers and consumers test services on a continuous basis. SOA's main goal is to deliver Agility to Businesses. Therefore it is important to invest in a testing framework (build or buy) that would provide you with the visibility required to find the culprit in your architecture in no time. The Business Agility requires from SOA services to be controlled by the business goals and directives as defined in the Business Motivation Model (BMM)[18].

Another challenge relates to providing appropriate levels of security. Security models built into an application may no longer suffice when the capabilities of the application are exposed as services that can be used by other applications. That is, application-managed security is not the right model for securing services. A number of new technologies and standards are emerging to provide more appropriate models for security in SOA. See SOA Security entry for more information.

As SOA and the WS-* specifications practitioners constantly expand, update and refine their output, there is a shortage of skilled people to work on SOA-based systems, including the integration of services and construction of services infrastructure.

Interoperability becomes an important aspect of SOA implementations. The WS-I organization has developed Basic Profile (BP) and Basic Security Profile (BSP) to enforce compatibility[19]. Testing tools have been designed by WS-I to help assess whether web services are conformant with WS-I profile guidelines. Additionally, another charter has been established to work on the Reliable Secure Profile.

Significant vendor hype exists concerning SOA; this can create expectations that may not be fulfilled. Product stacks continue to evolve as early adopters test the development and runtime products with real-world problems. SOA does not guarantee reduced IT costs, improved systems agility or faster time-to-market. Successful SOA implementations may realize some or all of these benefits depending on the quality and relevance of the system architecture and design[20] [21].

SOA efforts are routinely initiated by internal IT delivery organizations, and some of these improperly introduce concepts to the business so it remains misunderstood. The adoption starts meeting IT delivery needs instead of those of the business, so the result is an organization with superlative laptop provisioning services, instead of one that can quickly respond to market opportunities. Business Leadership also becomes convinced that the organization is executing on SOA well.

As one of the most important benefits of SOA is its ease of reuse. Therefore accountability and funding models must ultimately evolve within the organization. A business unit needs to be encouraged to create services that other units will use. Conversely, units must be encouraged to reuse services. This requires a few new governance components:

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Each business unit creating services must have an appropriate support structure in place to deliver on its service level obligations, and to support enhancing existing services strictly for the benefit of others. This is typically quite foreign to business leaders.

Each business unit consuming services accepts the apparent risk of reusing services outside their own control, with the attendant external project dependancies, etc.

An innovative funding model is needed as incentive to drive these behaviors above. Business units normally pay the IT Organization to assist during projects, and then to operate the environment. Corporate incentives should discount these costs to service providers, and create internal revenue streams from consuming business units to the service provider. These streams should be less than the costs of a consumer simply building it the old-fashioned way. ----

1.3.3 [edit] Criticisms of SOA

Some criticisms[22] of SOA depend on the assumption that SOA is just another term for Web Services. For example, some critics[who?] claim SOA results in the addition of XML layers, introducing XML parsing and composition. In the absence of native or binary forms of Remote Procedure Call (RPC), applications could run slower and require more processing power, increasing costs. Most implementations do incur these overheads, but SOA can be implemented using technologies (for example, Java Business Integration (JBI)) that do not depend on remote procedure calls or translation through XML. At the same time, there are emerging, open-source XML parsing technologies, such as VTD-XML, and various XML-compatible binary formats that promise to significantly improve the SOA performance[23][24][25].

Stateful services require both the consumer and the provider to share the same consumer-specific context, which is either included in or referenced by messages exchanged between the provider and the consumer. This constraint has the drawback that it could reduce the overall scalability of the service provider because it might need to remember the shared context for each consumer. It also increases the coupling between a service provider and a consumer and makes switching service providers more difficult.

Another concern is that WS-* standards and products are still evolving (e. g., transaction, security), and SOA can thus introduce new risks unless properly managed and estimated with additional budget and contingency for additional Proof of Concept work.

Some critics[who?] feel SOA is merely an obvious evolution of currently well-deployed architectures (open interfaces, etc).

A SOA being an architecture is the first stage of representing the system components that interconnect for the benefit of the business. At this level a SOA is just an evolution

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of an existing architecture and business functions. SOAs are normally associated with interconnecting back-end transactional systems that are accessed via web services.

The real issue with any IT "architecture" is how one defines the information management model and operations around it that deal with information privacy, reflect the business' products and services, enable services to be delivered to the customers, allow for self care, preferences and entitlements and at the same time embrace identity management and agility. On this last point, system modification (agility) is a critical issue that is normally omitted from IT system design. Many systems, including SOAs, hard-code the operations, goods and services of the organization, thus restricting their online service and business agility in the global marketplace.

Adopting SOAs is therefore just the first step in defining a real business system. The next step in the design process covers the definition of a Service Delivery Platform (SDP) and its implementation. It is in the SDP design phase where one defines the business information models, identity management, products, content, devices, and the end user service characteristics, as well as how agile the system is so that it can deal with the evolution of the business and its customers.

1.4 [edit] Extensions

1.4.1 [edit] SOA, Web 2.0, and mashups

Web 2.0 refers to a "second generation" of Web sites, primarily distinguished by the ability of visitors to contribute information for collaboration and sharing. Web 2.0 applications use Web services and may include AJAX, Flash, or JavaFX user interfaces, Web syndication, blogs, and wikis. While there are no set standards for Web 2.0, it is characterized by building on the existing Web server architecture and using services. Web 2.0 can therefore be regarded as displaying some SOA characteristics[26][27][28].

Some commentators[who?] also regard mashups as Web 2.0 applications. The term Enterprise mashups has been coined to describe Web applications that combine content from more than one source into an integrated experience that share many of the characteristics of service-oriented business applications (SOBAs). SOBAs are applications composed of services in a declarative manner. There is ongoing debate about "the collision of Web 2.0, mashups, and SOA," with some stating that Web 2.0 applications are a realization of SOA composite and business applications[29].

1.4.2 [edit] Web 2.0

Tim O'Reilly coined the term Web 2.0 to describe a perceived, quickly growing set of Web-based applications[30]. A topic that has experienced extensive coverage involves

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the relationship between Web 2.0 and Service-Oriented Architectures (SOAs). SOA is considered as the philosophy of encapsulating application logic in services with a uniformly defined interface and making these publicly available via discovery mechanisms. The notion of complexity-hiding and reuse, but also the concept of loosely coupling services has inspired researchers to elaborate on similarities between the two philosophies, SOA and Web 2.0, and their respective applications. Some argue Web 2.0 and SOA have significantly different elements and thus can not be regarded “parallel philosophies”, whereas others consider the two concepts as complementary and regard Web 2.0 as the global SOA[31].

The philosophies of Web 2.0 and SOA serve different user needs and thus expose differences with respect to the design and also the technologies used in real-world applications. However, very recently, numerous novel use-cases demonstrate the great potential of combining technologies and principles of both Web 2.0 and SOA[32].

In an "Internet of Services", all people, machines, and goods will have access via the network infrastructure of tomorrow. The Internet will thus offer services for all areas of life and business, such as virtual insurance, online banking and music, and so on. Those services will require a complex services infrastructure including Service delivery platforms bringing together demand and supply. Building blocks for the Internet of Services are SOA, Web 2.0 and semantics on the technology side as well as novel business models, and approaches to systematic and community based innovation[33].

Even though Oracle indicates that Gartner is coining a new term, Gartner analysts indicate that they call this advanced SOA and "whimsically" refer to it as SOA 2.0[34]. Most of the major middleware vendors (e. g., webMethods, TIBCO Software, IBM, Sun Microsystems, and Oracle) have had some form of SOA 2.0 attributes for years.

However, some other industry commentators[who?] have criticized attaching a version number ("2.0") to an application-architecture design-approach, while others[who?] have stated that the "next generation" should apply to the evolution of SOA techniques from IT optimization to business development[35].

1.5 [edit] See also

Big ball of mud anti-pattern Business-Agile Enterprise Business-driven development Business Intelligence 2.0 (BI 2.0) Comparison of business integration

software Digital signature

Wikimedia Commons has media related to: Service-oriented architecture

Public key infrastructure Representational State Transfer SAP Enterprise Services

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Enterprise application integration Enterprise Integration Patterns Enterprise Messaging System Enterprise service bus Event-driven programming Integration Objects Java Business Integration Microsoft Connected Services

Framework Open ESB Oracle SOA Suite

Architecture Search oriented architecture

complementary pattern Semantic service oriented

architecture – contain ISO standards

Service bureau Service component architecture Service layer Service-oriented analysis and

design Service-oriented architecture

implementation framework Service-oriented modeling SOA Governance Software as a service Software as a service Integration Sun Java CAPS Web Oriented Architecture

1.6 [edit]

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2 http://es.wikipedia.org/wiki/Arquitectura_orientada_a_servicios

2.1 Arquitectura orientada a servicios

Saltar a navegación, búsqueda

La Arquitectura Orientada a Servicios (en inglés Service Oriented Architecture), es un concepto de arquitectura de software que define la utilización de servicios para dar soporte a los requisitos del negocio.

Permite la creación de sistemas altamente escalables que reflejan el negocio de la organización, a su vez brinda una forma estándar de exposición e invocación de servicios (comúnmente pero no exclusivamente servicios web), lo cual facilita la interacción entre diferentes sistemas propios o de terceros.

SOA define las siguientes capas de software:

Aplicaciones básicas - Sistemas desarrollados bajo cualquier arquitectura o tecnología, geográficamente dispersos y bajo cualquier figura de propiedad;

De exposición de funcionalidades - Donde las funcionalidades de la capa aplicativas son expuestas en forma de servicios (servicios web);

De integración de servicios - Facilitan el intercambio de datos entre elementos de la capa aplicativa orientada a procesos empresariales internos o en colaboración;

De composición de procesos - Que define el proceso en términos del negocio y sus necesidades, y que varía en función del negocio;

De entrega - donde los servicios son desplegados a los usuarios finales.

SOA proporciona una metodología y un marco de trabajo para documentar las capacidades de negocio y puede dar soporte a las actividades de integración y consolidación.

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2.2 Contenido

[ocultar]

1 Definiciones SOA 2 Diseño y desarrollo de SOA 3 Lenguajes de alto nivel 4 Diferencias con otras arquitecturas 5 Beneficios 6 Literatura 7 Enlaces externos

2.3 Definiciones SOA [editar]

Término Definición / Comentario

Servicio Una función sin estado (Existen servicios asíncronos en los que una solicitud a un servicio crea, por ejemplo, un archivo, y en una segunda solicitud se obtiene ese archivo), auto-contenida, que acepta una(s) llamada(s) y devuelve una(s) respuesta(s) mediante una interfaz bien definida. Los servicios pueden también ejecutar unidades discretas de trabajo como serían editar y procesar una transacción. Los servicios no dependen del estado de otras funciones o procesos. La tecnología concreta utilizada para prestar el servicio no es parte de esta definición.

Orquestación Secuenciar los servicios y proveer la lógica adicional para procesar datos. No incluye la presentación de los datos. Coordinación.

Sin estado No mantiene ni depende de condición pre-existente alguna. En una SOA los servicios no son dependientes de la condición de ningún otro servicio. Reciben en la llamada toda la información que necesitan para dar una respuesta. Debido a que los servicios son "sin estado", pueden ser secuenciados (orquestados) en numerosas secuencias (algunas veces llamadas tuberías o pipelines) para realizar la lógica del negocio.

Proveedor La función que brinda un servicio en respuesta a una llamada o petición desde un consumidor.

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Consumidor La función que consume el resultado del servicio provisto por un proveedor.

2.4 Diseño y desarrollo de SOA [editar]

La metodología de modelado y diseño para aplicaciones SOA se conoce como análisis y diseño orientado a servicios. La arquitectura orientada a servicios es tanto un marco de trabajo para el desarrollo de software como un marco de trabajo de implementación. Para que un proyecto SOA tenga éxito los desarrolladores de software deben orientarse ellos mismos a esta mentalidad de crear servicios comunes que son orquestados por clientes o middleware para implementar los procesos de negocio. El desarrollo de sistemas usando SOA requiere un compromiso con este modelo en términos de planificación, herramientas e infraestructura.

Cuando la mayoría de la gente habla de una arquitectura orientada a servicios están hablando de un juego de servicios residentes en Internet o en una intranet, usando servicios web. Existen diversos estándares relacionados a los servicios web. Incluyen los siguientes:

XML HTTP SOAP WSDL UDDI

Hay que considerar, sin embargo, que un sistema SOA no necesariamente necesita utilizar estos estándares para ser "orientado a servicios" pero es altamente recomendable su uso.

En un ambiente SOA, los nodos de la red hacen disponibles sus recursos a otros participantes en la red como servicios independientes a los que tienen acceso de un modo estandarizado. La mayoría de las definiciones de SOA identifican la utilización de Servicios Web (empleando SOAP y WSDL) en su implementación, no obstante se puede implementar SOA utilizando cualquier tecnología basada en servicios.

2.5 Lenguajes de alto nivel [editar]

Los lenguajes de alto nivel como BPEL o WS-coordinación llevan el concepto de servicio un paso adelante al proporcionar métodos de definición y soporte para flujos de trabajo y procesos de negocio.

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2.6 Diferencias con otras arquitecturas [editar]

Al contrario de las arquitecturas orientado a objetos, las SOAs están formadas por servicios de aplicación débilmente acoplados y altamente interoperables. Para comunicarse entre sí, estos servicios se basan en una definición formal independiente de la plataforma subyacente y del lenguaje de programación (p.ej., WSDL). La definición de la interfaz encapsula (oculta) las particularidades de una implementación, lo que la hace independiente del fabricante, del lenguaje de programación o de la tecnología de desarrollo (como Plataforma Java o Microsoft.NET). Con esta arquitectura, se pretende que los componentes software desarrollados sean muy reusables, ya que la interfaz se define siguiendo un estándar; así, un servicio C Sharp podría ser usado por una aplicación Java.

2.7 Beneficios [editar]

Los beneficios que puede obtener una organización que adopte SOA son:

Mejora en los tiempos de realización de cambios en procesos. Facilidad para evolucionar a modelos de negocios basados en tercerización. Facilidad para abordar modelos de negocios basados en colaboración con otros

entes (socios, proveedores). Poder para reemplazar elementos de la capa aplicativa SOA sin disrupción en el

proceso de negocio Facilidad para la integración de tecnologías disímiles

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3 http://www.service-architecture.com/web-services/articles/service-oriented_architecture_soa_definition.html

A service-oriented architecture is essentially a collection of services. These services communicate with each other. The communication can involve either simple data passing or it could involve two or more services coordinating some activity. Some means of connecting services to each other is needed.

Service-oriented architectures are not a new thing. The first service-oriented architecture for many people in the past was with the use DCOM or Object Request Brokers (ORBs) based on the CORBA specification. For more on DCOM and CORBA, see Prior service-oriented architectures (new window).

3.1 Services

If a service-oriented architecture is to be effective, we need a clear understanding of the term service. A service is a function that is well-defined, self-contained, and does not depend on the context or state of other services. See Service (new window).

3.2 Connections

The technology of Web services (new window) is the most likely connection technology of service-oriented architectures. Web services essentially use XML (new window) to create a robust connection.

The following figure illustrates a basic service-oriented architecture. It shows a service consumer at the right sending a service request message to a service provider at the left. The service provider returns a response message to the service consumer. The request and subsequent response connections are defined in some way that is understandable to both the service consumer and service provider. How those connections are defined is explained in Web Services explained (new window). A service provider can also be a service consumer.

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4 http://webservices.xml.com/pub/a/ws/2003/09/30/soa.html

"Things should be made as simple as possible, but no simpler." -- Albert Einstein

4.1.1 Introduction

Einstein made that famous statement many decades ago, and it's still relevant today for building superior software systems. Unfortunately, as anyone who has been in the IT industry for long can point out, far too many software systems have failed Einstein's test. Some are made too simple to carry out the duties they are supposed to perform. Others are made too complex, and the costs of building and maintaining them have rocketed, not to mention the nearly impossible tasks of integrating different systems together. It seems that reaching the right level of simplicity is more like a dream than reality. Where have we gone wrong?

4.1.2 Loose Coupling

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We don't have to look far to find the problems. As we build more and more software systems, we see similar situations and patterns appearing. Naturally, we want to reuse the functionality of existing systems rather than building them from scratch. A real dependency is a state of affairs in which one system depends on the functionality provided by another. If the world only contained real dependencies, Einstein's test would have been satisfied long time ago. The problem is that we also create artificial dependencies along with real dependencies.

If you travel overseas on business, you know that you must bring power adapters along with you or your life will be miserable. The real dependency is that you need power; the artificial dependency is that your plug must fit into the local outlet. Looking at all the varying sizes and shapes of those plugs from different countries, you would notice that some of them are small and compact while many others are big and bulky.

The lesson here is that we cannot remove artificial dependencies, but we can reduce them. If the artificial dependencies among systems have been reduced, ideally, to their minimum, we have achieved loose coupling. In that sense, Einstein was just talking about was loose coupling. We might rework his famous principle thus: "Artificial

Related Reading

Web Services Essentials Distributed Applications with XML-RPC, SOAP, UDDI & WSDL By Ethan Cerami

Table of Contents Index Sample Chapter Read Online--Safari Search this book on Safari:

Code Fragments only

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dependencies should be reduced to the minimum but real dependencies should not be altered."

4.1.3 SOA Defined and Explained

Now we are able to define a Service Oriented Architecture (SOA). SOA is an architectural style whose goal is to achieve loose coupling among interacting software agents. A service is a unit of work done by a service provider to achieve desired end results for a service consumer. Both provider and consumer are roles played by software agents on behalf of their owners.

This sounds a bit too abstract, but SOA is actually everywhere. Let's look at an example of SOA which is likely to be found in your living room. Take a CD for instance. If you want to play it, you put your CD into a CD player and the player plays it for you. The CD player offers a CD playing service. Which is nice because you can replace one CD player with another. You can play the same CD on a portable player or on your expensive stereo. They both offer the same CD playing service, but the quality of service is different.

The idea of SOA departs significantly from that of object oriented programming, which strongly suggests that you should bind data and its processing together. So, in object oriented programming style, every CD would come with its own player and they are not supposed to be separated. This sounds odd, but it's the way we have built many software systems.

The results of a service are usually the change of state for the consumer but can also be a change of state for the provider or for both. After listening to the music played by your CD player, your mood has changed, say, from "depressed" to "happy". If you want an example that involves the change of states for both, dining out in a restaurant is a good one.

The reason that we want someone else to do the work for us is that they are experts. Consuming a service is usually cheaper and more effective than doing the work ourselves. Most of us are smart enough to realize that we are not smart enough to be expert in everything. The same rule applies to building software systems. We call it "separation of concerns", and it is regarded as a principle of software engineering.

How does SOA achieve loose coupling among interacting software agents? It does so by employing two architectural constraints:

1. A small set of simple and ubiquitous interfaces to all participating software agents. Only generic semantics are encoded at the interfaces. The interfaces should be universally available for all providers and consumers.

2. Descriptive messages constrained by an extensible schema delivered through the interfaces. No, or only minimal, system behavior is prescribed by messages.

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A schema limits the vocabulary and structure of messages. An extensible schema allows new versions of services to be introduced without breaking existing services.

As illustrated in the power adapter example, interfacing is fundamentally important. If interfaces do not work, systems do not work. Interfacing is also expensive and error-prone for distributed applications. An interface needs to prescribe system behavior, and this is very difficult to implement correctly across different platforms and languages. Remote interfaces are also the slowest part of most distributed applications. Instead of building new interfaces for each application, it makes sense to reuse a few generic ones for all applications.

Since we have only a few generic interfaces available, we must express application-specific semantics in messages. We can send any kind of message over our interfaces, but there are a few rules to follow before we can say that an architecture is service oriented.

First, the messages must be descriptive, rather than instructive, because the service provider is responsible for solving the problem. This is like going to a restaurant: you tell your waiter what you would like to order and your preferences but you don't tell their cook how to cook your dish step by step.

Second, service providers will be unable to understand your request if your messages are not written in a format, structure, and vocabulary that is understood by all parties. Limiting the vocabulary and structure of messages is a necessity for any efficient communication. The more restricted a message is, the easier it is to understand the message, although it comes at the expense of reduced extensibility.

Third, extensibility is vitally important. It is not difficult to understand why. The world is an ever-changing place and so is any environment in which a software system lives. Those changes demand corresponding changes in the software system, service consumers, providers, and the messages they exchange. If messages are not extensible, consumers and providers will be locked into one particular version of a service. Despite the importance of extensibility, it has been traditionally overlooked. At best, it was regarded simply as a good practice rather than something fundamental. Restriction and extensibility are deeply entwined. You need both, and increasing one comes at the expense of reducing the other. The trick is to have a right balance.

Fourth, an SOA must have a mechanism that enables a consumer to discover a service provider under the context of a service sought by the consumer. The mechanism can be really flexible, and it does not have to be a centralized registry.

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4.1.4 Additional Constraints

There are a number of additional constraints one can apply on SOA in order to improve its scalability, performance and, reliability.

4.1.4.1 Stateless Service

Each message that a consumer sends to a provider must contain all necessary information for the provider to process it. This constraint makes a service provider more scalable because the provider does not have to store state information between requests. This is effectively "service in mass production" since each request can be treated as generic. It is also claimed that this constraint improves visibility because any monitoring software can inspect one single request and figure out its intention. There are no intermediate states to worry about, so recovery from partial failure is also relatively easy. This makes a service more reliable.

4.1.4.2 Stateful Service

Stateful service is difficult to avoid in a number of situations. One situation is to establish a session between a consumer and a provider. A session is typically established for efficiency reasons. For example, sending a security certificate with each request is a serious burden for both any consumer and provider. It is much quicker to replace the certificate with a token shared just between the consumer and provider. Another situation is to provide customized service.

Stateful services require both the consumer and the provider to share the same consumer-specific context, which is either included in or referenced by messages exchanged between the provider and the consumer. The drawback of this constraint is that it may reduce the overall scalability of the service provider because it may need to remember the shared context for each consumer. It also increases the coupling between a service provider and a consumer and makes switching service providers more difficult.

4.1.4.3 Idempotent Request

Duplicate requests received by a software agent have the same effects as a unique request. This constraint allows providers and consumers to improve the overall service reliability by simply repeating the request if faults are encountered.

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4.1.5 Deriving Web Services from SOA

Everyone knows roughly what a "web service" is, but there is no universally accepted definition. The definition of web service has always been under hot debate within the W3C Web Services Architecture Working Group. Despite the difficulty of defining web services, it is generally accepted that a web service is a SOA with at least the following additional constraints:

1. Interfaces must be based on Internet protocols such as HTTP, FTP, and SMTP. 2. Except for binary data attachment, messages must be in XML.

There are two main styles of Web services: SOAP web services and REST web services.

4.1.5.1 SOAP Web services

A SOAP web service introduces the following constraints:

1. Except for binary data attachment, messages must be carried by SOAP. 2. The description of a service must be in WSDL.

A SOAP web service is the most common and marketed form of web service in the industry. Some people simply collapse "web service" into SOAP and WSDL services. SOAP provides "a message construct that can be exchanged over a variety of underlying protocols" according to the SOAP 1.2 Primer. In other words, SOAP acts like an envelope that carries its contents. One advantage of SOAP is that it allows rich message exchange patterns ranging from traditional request-and-response to broadcasting and sophisticated message correlations. There are two flavors of SOAP web services, SOAP RPC and document-centric SOAP web service. SOAP RPC web services are not SOA; document-centric SOAP web services are SOA.

4.1.5.2 SOAP RPC Web Services

A SOAP RPC web service breaks the second constraint required by an SOA. A SOAP RPC Web service encodes RPC (remote procedure calls) in SOAP messages. In other words, SOAP RPC "tunnels" new application-specific RPC interfaces though an underlying generic interface. Effectively, it prescribes both system behaviors and application semantics. Because system behaviors are very difficult to prescribe in a distributed environment, applications created with SOAP RPC are not interoperable by nature. Many real life implementations have confirmed this.

Faced with this difficulty, both WS-I basic profile and SOAP 1.2 have made the support of RPC optional. RPC also tends to be instructive rather than descriptive, which is against the spirit of SOA. Ironically, SOAP was originally designed just for RPC. It won't be long before someone claims that "SOAP" actually stands for "SOA Protocol".

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4.1.5.3 REST Web Services

The term REST was first introduced by Roy Fielding to describe the web architecture. A REST web service is an SOA based on the concept of "resource". A resource is anything that has a URI. A resource may have zero or more representations. Usually, people say that a resource does not exist if no representation is available for that resource. A REST web service requires the following additional constraints:

1. Interfaces are limited to HTTP. The following semantics are defined: o HTTP GET is used for obtaining a representation of a resource. A

consumer uses it to retrieve a representation from a URI. Services provided through this interface must not incur any obligation from consumers.

o HTTP DELETE is used for removing representations of a resource. o HTTP POST is used for updating or creating the representations of a

resource. o HTTP PUT is used for creating representations of a resource.

2. Most messages are in XML, confined by a schema written in a schema language such as XML Schema from W3C or RELAX NG.

3. Simple messages can be encoded with URL encoding. 4. Service and service providers must be resources while a consumer can be a

resource.

REST web services require little infrastructure support apart from standard HTTP and XML processing technologies, which are now well supported by most programming languages and platforms. REST web services are simple and effective because HTTP is the most widely available interface, and it is good enough for most applications. In many cases, the simplicity of HTTP simply outweighs the complexity of introducing an additional transport layer.

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5 http://tecnologia.infobaeprofesional.com/notas/46399-Que-es-SOA-la-arquitectura-orientada-a-servicios.html?cookie

5.1 ¿Qué es SOA, la arquitectura orientada a servicios?

D. Marsili, de Sybase, explica los alcances de esta tendencia cuya adopción crece en las áreas de tecnología de la información de las grandes empresas

La urgencia de datos, la exactitud y la seguridad a partir de un final de un proceso de negocio al otro son ahora un mandato de negocio. Las organizaciones que pueden hacer esto tienen una distintiva ventaja competitiva.

Pero la integración por la integración no es el objetivo exclusivo. El objetivo final de contar con un sistema unificado, significa para las compañías estar preparadas para cambiar sus focos y recursos desde el mantenimiento de las aplicaciones separadas al desarrollo de procesos de negocios de punta a punta basados en el servicio al cliente.

Asimismo, la flexibilidad de un sistema unificado hace esto posible para cambiar aquellos procesos en una respuesta rápida a los cambios en las necesidades de los negocios.

La arquitectura orientada a servicios (SOA) no se trata de software o de un lenguaje de programación, SOA es un marco de trabajo conceptual que permite a las organizaciones unir los objetivos de negocio con la infraestructura de TI integrando los datos y la lógica de negocio de sus sistemas separados.

Desarrollada a finales de los ´90, SOA establece un marco de trabajo para servicios de red – o tareas comunes de negocios – para identificar el uno al otro y comunicarlo.

La necesidad de tal marco se deriva de la evolución del software de negocio. En los comienzos, los desarrollos de aplicaciones de negocio se concentraban en necesidades específicas: contabilidad, compras, nómina de sueldos, transporte. Cada aplicación fue desarrollada sin consideración de otros sistemas en la empresa y como comunicarse con ellos. Porque las aplicaciones eran auto suficientes, la información común a toda la

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empresa (como por ejemplo: la dirección del cliente) y funciones específicas de negocios (como por ejemplo: buscar un nombre) aparecían en todas partes y requerían un código complejo para, todos o muchos de los sistemas independientes.

Por consiguiente, los diversos sistemas de TI de la mayoría de las empresas hoy no pueden acceder o procesar los datos desde el uno al otro. Un simple proceso de negocio (como una venta para un pedido a un depósito enviado a una cuenta por cobrar) que tomaría segundos si los sistemas se podrían comunicar, ahora puede tomar semanas.

¿Qué puede hacer una empresa? Debería tener inversiones masivas en hardware, software y perfiles de individuos involucrados en la ejecución de cada una de las aplicaciones separadas? Con SOA, una empresa puede mantener sus inversiones en los sistemas legacy y la gente necesaria para mantenerlos. Esto evita continuos y costosos proyectos "de integración", como las mejoras a cualquier aplicación son transparentes a todas las otras. La información de negocio es siempre "hasta el último minuto", permitiendo mejores decisiones de negocio y mejorar las relaciones entre clientes y partners.

A menudo, SOA es una solución prometedora para los problemas de integración. El desafío es cómo llegar ahí.

Cómo crear un ambiente SOA

El desarrollo de un ambiente SOA involucra un número de pasos. El primer paso es asegurar que todo el software nuevo que se instale sea compatible con SOA. El segundo paso es identificar las funciones dentro de los sistemas legacy que desean integrar y publicarlas como servicios. Por supuesto, esto no es tan fácil como suena. El desarrollo de estos servicios puede requerir de perfiles que no existen en la empresa. Y las herramientas necesarias para examinar los desarrollos y las etapas de despliegue pueden venir de diferentes proveedores, cada uno con su propia instalación, entrenamiento y temas de comunicación. El Desarrollo de Aplicaciones Orientadas a Servicios (SODA) está diseñado para vencer muchos de los problemas de lenguajes de software inherentes en los sistemas legacy. SODA permite reutilizar aplicaciones existentes y proveer un camino para construir nuevas, basadas en estándares, con interfases flexibles.

Esta adopción habilita un alto nivel de abstracción tecnológica. Es decir, SODA encapsula y abstrae tecnologías tales como bases de datos, J2EE, .NET y CORBA de modo que los desarrolladores no afronten la complejidad técnica de la interacción con aplicaciones heterogéneas y sistemas de infraestructura. SODA así reduce significativamente el esfuerzo requerido para traducir nuevos desafíos de negocios dentro de aplicaciones funcionales

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6 http://www.mastermagazine.info/articulo/3391.php

Conceptos básicos de la Arquitectura Orientada a Servicios De acuerdo a analistas de la industria, los conceptos básicos de la Arquitectura Orientada a Servicios (SOA) se establecieron desde hace 20 años. Por tanto, ¿qué ofrece de nuevo?, ¿por qué esta tecnología tiene tanto éxito mientras otras fallan? Durante esta serie de cinco capítulos, BEA Systems, líder mundial en infraestructura de aplicaciones y pionero del SOA, responderá todo lo que usted quiere saber sobre ésta, en apoyo a la gira mundial del dev2dev days 2004 en 23 ciudades del mundo, incluyendo México.

¿Cuáles son los elementos del SOA más importantes para su éxito? Como primer punto se encuentra la flexibilidad. SOA es la primera arquitectura de Tecnologías de Información (TI) que asume lo que los negocios han sabido desde hace mucho tiempo. Se trata esencialmente de un set de servicios sueltos, donde cada uno es relativamente económico para construirlo o reemplazarlo si es necesario. Al ser independientes, el poder unirlos permite a SOA adaptar cambios, cuestión imposible para arquitecturas tradicionales. En la Arquitectura Orientada a Servicios, se puede reemplazar un servicio sin tener que preocuparse por la tecnología fundamental; la interfase es lo que importa, y está definida en un estándar universal en servicios Web y XML. Esto es flexibilidad a través de la interoperabilidad. También es la habilidad de asegurar los activos existentes, aplicaciones y bases de datos legales y hacerlos parte de las soluciones empresariales extendiéndolos al SOA en vez de reemplazarlos. El resultado en la red es la habilidad de evolucionar rápida y eficientemente, en otras palabras, adaptarse “orgánicamente” de acuerdo a la demanda del negocio. Esto es realmente nuevo. En segundo lugar está la relevancia para el negocio. SOA es TI expresada a un nivel que tiene un significado importante para la colaboración del negocio y profesionales del área. Sus servicios actuales pueden coordinar unidades de trabajo muy cercanas a las actividades del negocio; piense, por ejemplo, en un servicio llamado “Actualización de órdenes de trabajo”. Éstos son inmediatamente relevantes para los analistas de la empresa que participan en la creación y definición de nuevos procesos permitiendo el “Servicio Dirigido Empresarial”. Desde que los servicios web sustituyen la mayoría de las tecnologías fundamentales, muy poca tecnología de habla es requerida. Los negocios y las TI se enfocan en la lógica del negocio y la comunicación; finalmente comparten el lenguaje de servicios. Esto también es relativamente nuevo y tendrá implicaciones en la entrega de servicios TI.

¿Cuáles son las principales barreras a vencer para obtener el éxito de SOA? SOA es un nuevo horizonte para las TI. Como cualquier gran cambio, las principales barreras son organizacionales, no técnicas. A continuación ejemplificaremos algunas: · Administración: Servicios compartidos es lo principal para utilizar SOA. La habilidad para ensamblar rápidamente aplicaciones o procesos está basada en la disponibilidad

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de algunos servicios que pueden ser compartidos. Hacer esto, por definición, requiere administración. · Desarrollo Cultural: Al utilizar SOA se requiere un cambio significativo en el estilo de programar. Muchos desarrolladores utilizan equipos diferentes para resolver problemas de manera independiente para cada aplicación. En SOA necesitarán escribir aplicaciones para ser re-utilizadas en mente, usando códigos existentes, a los cuales se podrá tener acceso constantemente.

¿Cómo se distingue actualmente SOA de anteriores estándares de integración y conectividad tales como CORBA? CORBA era mucho más ambicioso, tecnológicamente hablando, que SOA, y requería una tremenda habilidad de conocimientos en su implementación. Ésta es rara de encontrar, lo cual contribuyó a no entender el significado del estándar. SOA, en contaste, es sencillo y está basado en estándares universales, lo cual asegura que las habilidades para construir aplicaciones sean muy accesibles. En la Arquitectura Orientada a Servicios, la distribución de los beneficios permite un desarrollo óptimo de funciones como la “Actualización de órdenes de trabajo”. Con CORBA, la distribución de los beneficios eran aplicaciones con diferentes propiedades y métodos. Con SOA habrá menor control y poder, pero es más fácil de manejar. Técnicamente no será muy poderoso pero es muy inteligente en el rol de las organizaciones y personas que buscan el éxito en las TI.

¿Qué rol juega Java en el éxito potencial del SOA? Java es muy importante para un estándar de servicios. Las habilidades y herramientas que proporciona su comunidad garantiza calidad para construir en SOA. Así es como mutuamente contribuyen al éxito, ya que Java es una manera más para implementar servicios.

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7.1.1 SOA y los Servicios Web (I)

En la actualidad el concepto de SOA ha resurgido, gracias al auge y madurez de una nueva tecnología: los Servicios Web. Los Servicios Web se han convertido en el estandarte de SOA, ya que esta tecnología posee un conjunto de características que permiten cubrir todos los principios de la orientación a servicios, no como otras posibles tecnologías de implementación como colas de mensajes o CORBA. Centrándonos en los Servicios Web, podemos decir que con ellos se pueden generar dos tipos de Arquitecturas Orientadas a Servicios:

Arquitectura Orientada a Servicios Tradicional. Arquitectura Orientada a Servicios de segunda generación.

En el presente artículo describiré la primera de ellas.

La SOA Tradicional es aquella que utiliza los principios y tecnologías básicos de los Servicios Web. Esto significa utilizar SOAP como lenguaje de intercambio, WSDL como lenguaje para la descripción de los servicios y UDDI para la publicación o registro de los mismos. En el dibujo que se muestra a continuación, se puede ver la estructura básica de funcionamiento de una SOA tradicional.

En el gráfico anterior, se puede observar la existencia de tres roles claramente diferenciados:

Cliente del servicio: Es el que solicita la ejecución del servicio web, y por lo tanto el que lo consume.

Proveedor del servicio: Es el encargado de implementar el servicio web y ofrecerlo a los clientes.

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Registro del servicio: Es un repositorio donde se almacenan las descripciones de los servicios, para que así los clientes puedan buscar el servicio web que mejor se adapte a sus necesidades.

La secuencia de ejecución es la siguiente:

1. El proveedor del servicio da de alta el servicio web en el registro. Para realizar esto, el proveedor almacena en el registro el documento de descripción de este.

2. El solicitante del servicio busca en el registro un servicio web que pueda adaptarse a sus necesidades.

3. Una vez seleccionado el servicio, el solicitante lo invoca mediante el envío de un mensaje SOAP, en el cual se indica la acción a realizar y los datos de entrada.

4. El servicio web recibe la petición y ejecuta la funcionalidad. Para finalizar envía un mensaje SOAP al solicitante con los resultados obtenidos.

Por lo tanto, una SOA tradicional estará compuesta por un conjunto de servicios que reciben y envían mensajes SOAP en base a una descripción WSDL. Este tipo de arquitecturas hoy en día es muy utilizado, pero no es el más óptimo debido a que no porpociona una serie de características esenciales a la hora de crear una Arquitectura profesional. Estas características son:

Seguridad Transaccionabilidad Garantía de entrega Orquestación Coreografía Direccionamiento etc...

Estas características las ofrecen las SOA de segunda generación, que serán el tema central de otro artículo.

Este artículo se centra en el segundo tipo de Arquitecturas Orientadas a Servicios, que yo he denominado SOA de segunda generación. Es el tipo utilizado actualmente, porque está basado en el SOA tradicional, añadiendo lo necesario para cubrir sus carencias. Es decir, proporciona los elementos necesarios para cumplir con todos los principios de la orientación a objetos. El esquema básico de una SOA de segunda generación es el mostrado en el siguiente gráfico:

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Como se puede observar, una SOA de segunda generación está formada por un conjunto de Funciones y por la Calidad del Servicio. La Funciones están formadas por:

Transporte: Mecanismo utilizado para trasladar las peticiones desde el cliente, hasta el proveedor del servicio, y viceversa.

Protocolo de comunicación: Es el sistema de comunicación entre el cliente y el proveedor de servicios.

Descripción del servicio: Es un esquema utilizado para describir qué servicio es, como se le puede invocar, y cuales son los datos necesarios para realizar su invocación.

Servicio: Es la implementación del servicio. Proceso de negocio: Es una colección de servicios, invocados en una

determinada secuencia, con un conjunto particular de reglas para satisfaces un requisito de negocio.

Registro de servicios: Es un repositorio de servicios y datos, usado por los proveedores de servicio y publicar los servicios, y para los clientes, donde buscarlos.

La calidad del servicio por:

Política: Son un conjunto de reglas bajo las cuales, un proveedor de servicio hace que el servicio esté disponible para los clientes (WS-Policy).

Seguridad: Son un conjunto de reglas que podrían ser aplicadas en la identificación, autorización y control de acceso a los servicios, por parte del cliente (WS-Security).

Transacción: Conjunto de atributos que podrían ser aplicados sobre un grupo de servicios para devolver un conjunto de datos consistentes (WS-Transaction, WS-Coordination).

Gestión: Conjunto de atributos que podrían ser aplicados para gestionar los servicios proporcionados (WS-Manageability).

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Es decir, las SOA de segunda generación se basan en ampliar su funcionalidad mediante el uso de los estándares WS, que proporcionan funcionalidades como gestión de transacciones, seguridad, etc..

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8.1.1 Elementos esenciales de una Arquitectura Orientada a Servicios

En las Arquitecturas Orientadas a Servicios, el elemento básico es el servicio. Pero únicamente con este concepto, no podríamos diseñar una arquitectura SOA. Cuatro son los elementos esenciales necesarios para la construcción de una Arquitectura Orientada a Servicios:

1. Operación: Es la unidad de trabajo o procesamiento en una arquitectura SOA. 2. Servicio: Es un contenedor de lógica. Estará compuesto por un conjunto de

operaciones, las cuales las ofrecerá a sus usuarios. 3. Mensaje: Para poder ejecutar una determinada operación, es necesario un

conjunto de datos de entrada. A su vez, una vez ejecutada la operación, esta devolverá un resultado. Los mensajes son los encargados de encapsular esos datos de entrada y de salida.

4. Proceso de negocio: Son un conjunto de operaciones ejecutadas en una determinada secuencia (intercambiando mensajes entre ellas) con el objetivo de realizar una determinada tarea.

Por lo tanto, una aplicación SOA estará formada por un conjunto de procesos de negocio. A su vez esos procesos de negocio estarán compuestos por aquellos que servicios que proporcionan las operaciones que se necesitan ejecutar para que el

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proceso de negocio llegue a buen término. Por último para ejecutar esas operaciones es necesario el envío de los datos necesarios mediante los correspondientes mensajes.

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9.1.1 12 pasos para migrar a un entorno SOA

En la gran mayoría de los casos, el desarrollo de una Arquitectura Orientada a Servicios, suele ser la solución adoptada a la horas de migrar aplicaciones antiguas a nuevos entornos. Esto se debe a que una arquitectura SOA, aporta ventajas como escalabilidad, flexibilidad, reutilización, etc... (ya sabeis que opino yo de esto. Es verdad siempre y cuando se haya destinado un gran esfuerzo [tiempo+ dinero] a desarrollar esa arquitectura SOA). Para realizar una migración, es necesario diseñar un plan de ejecución. Pues bien, David S. Linthicum, gurú en el campo de SOA, ha definido en este documento los 12 pasos que deberían seguirse para realizar una migración con plenas garantías de éxito. Es un documento muy recomendable, puesto que nos puede proporcionar una visión global de la complejidad a la hora de migrar a SOA. Ahora bien, no penseis que el documento va a solucionar vuestros problemas y dudas trascendentales, puesto que en él se indican cuales son los pasos en un plan de migración, pero no se centra en las técnicas y herramientas para acometer ese plan.

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Un problema con el que nos podemos encontrar a la hora de construir una aplicación SOA es si la aplicación construida realmente es una aplicación "SOA Compliant". Para comprobar si una aplicación lo es, la mejor forma de hacerlo es chequeando que la aplicación cumpla con los Principios de la Orientación a Servicios. No existe una definición estándar de cuales son los Principios de la Orientación a Servicios, por lo tanto, lo único que se puede proporcionar es un conjunto de Principios que estén muy asociados con la Orientación a Servicios. Estos Principios según Thomas Erl son:

Los Servicios deben ser reusables: Todo servicio debe ser diseñado y construido pensando en su reutilización dentro de la misma aplicación, dentro del dominio de aplicaciones de la empresa o incluso dentro del dominio público para su uso masivo.

Los Servicios deben proporcionar un contrato formal: Todo servicio desarrollado, debe proporcionar un contrato en el cual figuren: el nombre del servicio, su forma de acceso, las funcionales que ofrece, los datos de entrada de cada una de las funcionalidades y los datos de salida. De esta manera, todo consumidor del servicio, accederá a este mediante el contrato, logrando así la indepencia entre el consumidor y la implementación del propio servicio. En el caso de los Servicios Web, esto se logrará medienta la definición de interfaces con WSDL.

Los Servicios deben tener bajo acoplamiento: Es decir, que los servicios tienen que ser independientes los unos de los otros. Para lograr ese bajo acoplamiento, lo que se hará es que cada vez que se vaya a ejecutar un servicio, se accederá a él a través del contrato, logrando así la independencia entre el servicio que se va a ejecutar y el que lo llama. Si conseguimos este bajo acoplamiento, entonces los servicios podrán ser totalmente reutilizables.

Los Servicios deben permitir la composición: Todo servicio debe ser construido de tal manera que pueda ser utilizado para construir servicios genéricos de más alto nivel, el cual estará compuesto de servicios de más bajo nivel. En el caso de los Servicios Web, esto se logrará mediante el uso de los protocolos para orquestación (WS-BPEL) y coreografía (WS-CDL).

Los Servicios deben de ser autónomos: Todo Servicio debe tener su propio entorno de ejecución. De esta manera el servicio es totalmente independiente y nos podemos asegurar que así podrá ser reutilizable desde el punto de vista de la plataforma de ejecución.

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Los Servicios no deben tener estado: Un servicio no debe guardar ningún tipo de información. Esto es así porque una aplicación está formada por un conjunto de servicios, lo que implica que si un servicio almacena algún tipo de información, se pueden producir problemas de inconsistencia de datos. La solución, es que un servicio sólo contenga lógica, y que toda información esté almacenada en algún sistema de información sea del tipo que sea.

Los Servicios deben poder ser descubiertos: Todo servicio debe poder ser descubierto de alguna forma para que pueda ser utilizado, consiguiendo así evitar la creación accidental de servicios que proporcionen las mismas funcionalidades. En el caso de los Servicios Web, el descubrimiento se logrará publicando los interfaces de los servicios en registros UDDI.

Cuando se desarrollan aplicaciones SOA es muy útil y necesario tener en cuenta siempre estos principios, ya que nos van a dar las pautas necesarias para tomar ciertas decisiones de diseño complejas.

Como se habrá podido observar, una característica muy importante de los Principios de la Orientación a Servicios, es que todos ellos se inter-relacionan. El siguiente gráfico muestra la inter-relación de los diferentes principios:

Como se puede observar en el gráfico, el objetivo de la Orientación a Servicios es obtener software totalmente reutilizable a través de un conjunto de técnicas y principios como los descritos anteriormente.