Context and Concept of Web Services

Fatih Taşkın

Definition

IBM: “A Web Service is a collection of functions that are packaged as a single entity and published to the network for use by other programs...[They are] self-describing, self-contained, modular applications...”(Glass, 2000).

World Wide Web Consortium (W3C): “A software system identified by a URI [uniform resource indicator], whose public interfaces and bindings are defined and described using XML [extensible markup language]. Its definition can be discovered by other software systems. These systems may then interact in a manner prescribed by its definition, using XML based messages conveyed by internet protocols” (W3C, 2002).

Distributed Computing Systems

• Computing was distributed over the networks instead of being performed on a single,centralized computer.

• The centralization of activities presented some problems in terms of scalability and flexibility.

Common Object Request BrokerArchitecture (CORBA)

• CORBA is an open-standards-based solution to distributed computing. The Object Management Group, an industry consortium, developed the specifications for CORBA.

• The primary advantage of CORBA is that clients and servers can be written in any programming language.

Distributed Component ObjectModel (DCOM)

• Microsoft’s DCOM has a layer that sits on the top of a remote procedure-calling (RPC) mechanism and allows calls to remote objects that interact with the COM run-time services.

Remote Method Invocation (RMI)

• RMI enables one to create Java-to-Java applications, in which the methods of remote Java objects can be invoked from other Java virtual machines.

• A Java program can make a call on the remote object once it obtains a reference to the remote object.

World Wide Web

• The transmission control protocol/ Internet protocol (TCP/IP) formed the common base protocol for connectivity.

• This was followed by the advent of various protocols like the hypertext transfer protocol (HTTP), file transfer protocol (FTP), and Gopher for specific needs.

• XML

Web Services Architecture

Service Requestor: This is the agent that requestsa service.

Service Provider: This is the owner of the service

Service Registry: This is a registry that contains allavailable services.

Web Services Protocols

• Service Invocation and Communication: Simple object access protocol (SOAP)

• Service Description: Web services description language (WSDL)

• Service Discovery: Universal description, discovery and integration (UDDI)

• Standard Transport Protocol: HTTP• Underlying Protocol: XML

Understanding Web Services

• The Web aspects of Web services– Web-Based Protocols: Web services are based on HTTP and thus are

designed to work over the public Internet.– Interoperability: The XML-based protocols used for communication in

SOAP define a common standard that allows differing systems to interoperate

• The service aspect– Modular: The service components are useful, are reusable, and

can be combined to form larger components.– Available: Services are available to systems that wish to use

them.– Described: Services have service descriptions,which are also

machine readable to identify the interface of the service.– Implementation Independent: The service interface must be

available in a way that is independent of the ultimate implementation.

Simple Object Access Protocol

• SOAP provides a simple and lightweight mechanism for exchanging structured and typed information between peers in a decentralized and distributed environment using XML

SOAP Parts

• SOAP Envelope Construct: Defines an overall framework for expressing what is in a message, who should deal with it, and whether it is optional or mandatory.

• SOAP Encoding Rules: Define a serialization mechanism that can be used to exchange instances of application-defined data types.

• •SOAP RPC Representation: Defines a convention that can be used to represent RPCs and responses.

Universal Description,Discovery, and Integration

• UDDI is a standard designed to facilitate a searchable directory of service providers.– Yellow-Pages Taxonomies: Here, searches can done

according to a particular industry, sector, or product category.– White Pages: This contains address information, contact

information, and the phone numbers of service providers.– Green Pages: This contains the technical details about the

service provider. It tells the service requestor the details as to how to invoke the request with that particular service provider.

Thank you and them

All text and visual materials were directly taken from

Essay of Context and Concept of Web Services – Vijay Kasi(Georgia State University, USA)– Brett Young(Georgia State University, USA)