soa and web services primer

8/6/2019 SOA and Web Services Primer

1/71

SOA & WEB SERVICES PRIMER


2/71

Introduction

Expectations & Objectives


3/71

Agenda

SOA

Web Services

Web Service design methodology (on a very high level)

Bottom up method Top down method

SOAP

The structure of SOAP messages: Envelope, Header and Body

WSDL

Structure of a WSDL and How to read a WSDLThe Message styles: RPC/Encoded, RPC/Literal, Document/Literal,

Wrapped and Bare

Comparison of the SOAP Engines Axis, Axis2, Metro and CXF


4/71

Key Terms

SOA

SOAP

WSDL

JBI

ESB


5/71

Service Oriented Architecture

SOA is a technical pattern for implementing cohesiveand loosely coupled (business and technical) functionswith well-defined interfaces.

Such services are consumed with the help of the detailsspecified in the interface without any knowledge ofthe implementation.


6/71


A service-oriented architecture is essentially a

collection of services.

These services communicate with each other.


7/71


A service is a function that is well-defined, self-contained, and does not depend on the context orstate of other services

The technology of web services is the most likelyconnection technology of service-orientedarchitectures.

Services

Connections


8/71

Advantages of SOA

They offer business services across the platforms

They provide location independence

Services need not be at a particular system or particularnetwork

Completely loosely coupled approach

Authentication and authorization support at every levelThe search and connectivity to other services is dynamic


9/71

Short-term benefits

Enhances reliability

Reduces hardware acquisition costs

Leverages existing development skills

Accelerates movement towards applicationconsolidation

Provides a data bridge between incompatibletechnologies


10/71

Long-term benefits

Provides the ability to build composite applications

Creates a self-healing infrastructure that reduces

management costsProvides truly real-time decision-making applications

Enables the compilation of a unified taxonomy ofinformation across an enterprise and its customer andpartners


11/71

Benefits from Business perspective

Ability to more quickly meet customer demands

Lower costs associated with the acquisition and

maintenance of technologyManagement of business functionality closer to the

business units

Leverages existing investments in technology

Reduces reliance on expensive custom development


12/71

Web Services


13/71

What is Web Service

Web Services can convert your application into a Web-application, which can publish its function or messageto the rest of the world.


14/71

Why Web Service


15/71

Services Provider, Service

Consumer, Registry

The figure above illustrates a basic service Request

Response

The request and subsequent response connections aredefined in some way that is understandable to both theservice consumer and service provider.

A service provider can also be a service consumer.


16/71

Types of Web Service

The three most common styles of use are RPC, SOA andREST.


17/71

RPC

RPC Web services present a distributed function (ormethod) call interface that is familiar with manydevelopers. Typically, the basic unit of RPC Webservices is the WSDL operation


18/71

SOA

Web services can also be used to implement anarchitecture according to Service-orientedarchitecture (SOA) concepts, where the basic unit ofcommunication is a message, rather than anoperation. This is often referred to as message-oriented services


19/71

REST

(REST) attempts to describe architectures which useHTTP or similar protocols by constraining theinterface to a set of well-known, standard operations(like GET, POST, PUT, DELETE for HTTP). Here, thefocus is on interacting with stateful resources, ratherthan messages or operations.


20/71

Web service design methodology

Web services can be written in two ways:

bottom up method

top down method


21/71


A developer using the "bottom up method" first writes theimplementing class in a programming language, and thenuses a WSDL generating tool to expose its methods as a web

service. This is often the simpler approach.


22/71


A developer using the "top down method" first writesthe WSDL document and then uses a code generatingtool to produce the class skeleton, which he latercompletes.


23/71

SOAP

Simple Object Access Protocol


24/71

SOAP Structure


25/71

SOAP Structure

A SOAP message is encoded as an XML document, consisting of an element, which contains an optional element,and a mandatory element. The element, containedwithin the , is used for reporting errors. The SOAP envelope The SOAP is the root element in every SOAP

message, and contains two child elements, an optional and amandatory .

The SOAP header The SOAP is an optional sub-element of the SOAPenvelope, and is used to pass application-related information that is to beprocessed by SOAP nodes along the message path.

The SOAP body The SOAP is a mandatory sub-element of the SOAPenvelope, which contains information intended for the ultimate recipient ofthe message.

The SOAP fault The SOAP is a sub-element of the SOAP body, which isused for reporting errors.

WSDL


26/71

WSDL

W b S i D i t L


27/71

Web Service Descriptor Language

WSDL is an XML-based language for describing Webservices and how to access them.

WSDL is used to describe Web servicesWSDL is also used to locate Web services

WSDL is a W3C recommendation

WSDL St t


28/71

WSDL Structure

Ab t t d C t


29/71

Abstract and Concrete

An abstract WSDL document describes what the web servicedoes, but not how it does it or how to contact it. Anabstract WSDL document defines:

the operations provided by the web service.

the input, output and fault messages used by each operation tocommunicate with the web service, and their format.

A concrete WSDL document adds the information abouthow the web service communicates and where you canreach it. A concrete WSDL document contains the abstractWSDL definitions, and also defines:

the communication protocols and data encodings used by the webservice.

the port address that must be used to contact the web service.

Th WSDL D t St t


30/71

The WSDL Document Structure

A typical WSDL document consists of the followingelements

Element Defines

Root WSDL element

What datatypes will be transmitted

What message will be transmitted

What operations (functions) will be supported

The communication protocols used by the web service

Where is the service located.

Used to provide human-readable documentation

To import other WSDL documents or XML Schemas


31/71

H t d WSDL


32/71

How to read a WSDL

The root element of a WSDL is definitions. So we startthe WSDL tree with a definition node as root

H t d WSDL (D fi iti )


33/71

How to read a WSDL (Definition)

The definition element specifies that this document isthe HelloService. It also specifies the numerousnamespaces that will be used throughout the

document.The use of namespaces is important for differentiating

elements, and it enables the document referencemultiple external specification. WSDL specification

SOAP specification and

XML schema specification

Ho to read a WSDL (Definition)


34/71


The definition element also specifies a targetNamespace

attribute. The targetNamespace is a convention of XMLschema that enables the WSDL document to refer to

itself.

In this example we specifed a targetNamespace ofhttp://www.ecerami.com/wsdl/HelloService.wsdl

Note: the namespace specification does not require that thedoucment actually exist at this location; the important

point is that you specify a value that is unique, different

from all other namespaces that are defined.

http://www.ecerami.com/wsdl/HelloService.wsdlhttp://www.ecerami.com/wsdl/HelloService.wsdl


35/71


The definition element specifies a default namespace:xmlns=http://schemas.xmlsoap.org/wsdl/ .

All the elements without a namespace prefic, such asmessage or porttype, are therefore assumed to bepart of the default WSDL namespace.

How to read a WSDL (Service)


36/71


To analyze a WSDL document it is recommended to read itfrom the bottom upwards.

At the bottom of the WSDL we find a child element namedservice



37/71


A Service may have one or more ports. Each portdescribes a way to access the service.



38/71


Its child element address has a different XML prefix thanthe other elements. (soap, soap12, http, etc.,)

How to read a WSDL (Binding)


39/71


To move on, we have to look at the binding attribute ofthe port.



40/71


A binding provides details about a specific transport.



41/71


The (wsdl:binding> element of the WSDL contains a pairof parameters that influence the form of the resultingSOAP messages :

Binding style (RPC or document) and

Use (encoded or literal)



42/71


The Style Attribute This choice corresponds to how theSOAP payload i.e., how the contents of the element can be structured.

Document The SOAP message is sent as one document in the element without additional formatting rules havingto be considered. The Document style is the default choice.

RPC The structure of an RPC style element needsto comly with the rules specified in detail in section 7 of the SOAP

1.1 specification. According to these rules, maycontain only one element that is named after the operation, andall parameters myst be represented as sub-elements of thiswrapper elements.



43/71


SOAP has its roots in synchronous remote procedurecalls over HTTP and the appearance of the documentaccordingly followed these conventions. Later, it wasseen as a simplification to use arbitary XML in the

SOAP body without adhering to conventions.

The choice of one or the other is mainly a question of

personal taste since most SOAP clients today acceptboth versions.



44/71


The Use Attribute This attribute specifies the encoding rulesof the SOAP message. It refers to the serialization rulesfollowed by the SOAP client and SOAP server to interpret thecontents of the element of the SOAP payload.

Literal Means that the type definitions literally follow an XML schemadefinition.

Encoded refers to the representation of application data in XML,usually according to the SOAP encoding rules of the SOAP 1.1specification. The rules to encode and interpret a SOAP body are in aURL specified by the encodingStyle attribute.

Encoded is the appropriate choice where non-treelike structures areconcerned, because all others can be perfectly described in XMLschema.



45/71


The combination of the style and use attributes leads tofour possible style/use pairs:

1. RPC/encoded

2. RPC/literal

3. Document/encoded

4. Document/literal



46/71


In the binding you can find the transport option for theoperation.

Inside the operation element there is a soap:operationelement defining details for the SOAP protocol and itstransport. The soapAction is a reminiscent from thepast and is used with a fixed value of an empty string.



47/71


Because Web Services set the focus on message not parameters,

information about the transport of these messages can be found in thewsdl:input and wsdl:output element.

A service may specify one or more faults as an alternative for the output.



48/71


The soap:body and soap:header elements can describe amessage further.

How to read a WSDL (PortType)


49/71


Time to move up in the WSDL. Now we follow the value of the type attribute of thebinding. It points to a portType with the same name further up in the document.

Now we have crossed the border from the concrete details about the transport andlocation of a service to its pure abstract description of its interface.



50/71


PortType is in WSDL 1.1 similar to the interface of theWeb Service.

In WSDL 2.0 the term portType is substituted with the

term interface.



51/71


An interface can have several operations.

An operation corresponds to a function in procedural programming.



52/71


Inside a portType we find operation element as in the

binding.

But this time the input and output describe the structure ofthe message not transport specific options

How to read a WSDL (Message)


53/71


The message attribute of the input refers again up in the

WSDL document.

Further up in the document we find a correspondingmessage with this name



54/71


The message element has one part element as child.

A WSDL specialist will recognize the value of the attribute name,parameters indicates the wrapper sub-style

How to read a WSDL (Types)


55/71


The next child of the definitions element is types



56/71


The types element can have multiple XML schema aschildren.



57/71


In a schema we can find the definition of : ComplexTypes SimpleTypes

and the declaration of:

Elements

In a document/literal style all the parts point to elements



58/71


A complex type with a sequence as content



59/71


A sequence consists of several elements that describethe order of elements in a SOAP message.

WSDL operations


60/71

WSDL operations

WSDL supports four basic patterns of operation: One Way

The service receives a message. The operation there has a single inputelement.

Request-responseThe service receives a message and sends a response. The operation

therefore has one input element and one output element. Toencapsulate errors, an optional fault element can be specified.

Solicit-responseThe service sends a message and receives a response. The operation

therefore has one output element, followed by one input element. To

encapsulate errors, an optional fault element can also be specified. Notification

The service sends a message. The operation therefore has a singleoutput element.

WSDL operations


61/71

WSDL operations

ESB


62/71

ESB

Enterprise Service Bus


63/71


A Standard based middleware architecture which allowspluggable components to communicate with eachother via a messaging system



64/71

p

Use of an ESB certainly implies adherence to a particulararchitecture

The term Enterprise Service Bus" almost always

denotes the software infrastructure that enables suchan architecture.



65/71

p

In essence, the ESB is considered a platform to realize aservice-oriented architecture.



66/71

p

An Enterprise Service Bus (ESB) brings flow-relatedconcepts such as

Transformation and

Routing

to a Service-Oriented Architecture.



67/71

p

Routing In a large enterprise with numerous applications and channels to connect them, a message may have to gothrough several channels to reach its final destination. The route a message must follow may be so complex that theoriginal sender does not know what channel will get the message to the final receiver. Instead, the original sendersends the message to a Message Router, an application component and filter in the pipes-and-filters architecture,which will determine how to navigate the channel topology and direct the message to the final receiver, or at least tothe next router.

Transformation Various applications may not agree on the format for the same conceptual data; the sender formatsthe message one way, yet the receiver expects it to be formatted another way. To reconcile this, the message mustgo through an intermediate filter, a Message Translator, that converts the message from one format to another.

Endpoints An application does not have some built-in capability to interface with a messaging system. Rather, it must

contain a layer of code that knows both how the application works and how the messaging system works, bridgingthe two so that they work together. This bridge code is a set of coordinated Message Endpoints that enable theapplication to send and receive messages.



68/71

p

An ESB can also provide an Abstraction for Endpoints.

This promotes flexibility in the Transportation Layer andenables loose coupling and easy connection betweenservices

JBI


69/71

Java Business Integration


70/71

g

Java Business Integration is a Java-based standardaddressing the EAI and B2B issues based on theparadigms and principles advocated by service-

oriented architecture.

The current version (1.0) is finalized through the JSR(Java Specification Request) 208 in August 2005. Both

commercial and open source worlds have alreadystarted embracing JBI as an integration standard intheir ESB products


71/71

Thank you

soa and web services primer

Documents