Web Service

Web Services Fundamentals

Two Competing Approaches

• REST-style
• SOAP-style

Four Fundamental Technologies

• XML
• Describing information sent over the network
• WSDL
• Defining web service capability
• SOAP
• Accessing web services
• UDDI
• Finding web services

Web Service Infrastructure and Components

XML

• Has emerged as the standard solution for describing information exchanged between heterogeneous system
• Can be read by programs and interpreted in an application-specific way
• Example
• <Account>xx</Account>

WSDL: Describing the web service

• Provides functional description of network services
• IDL description
• Protocol and deployment details
• Platform independent description
• Extensible language
• As extended IDL: WSDL allows tools to generate compatible client and server stubs
• Allows industries to define standardized service interfaces
• Allows advertisement of service descriptions, enables dynamic discovery and binding of compatible services
• Used in conjunction with UDDI registry
• The main elements in a WSDL description

UDDI: Finding Web Service

• Universal Description, Discovery, Integration
• UDDI defines the operation of a service registry
• Data structures for registering
• Business
• Technical specification: tModel is a keyed reference to a technical sepcifcaiton
• Service and service endpoints
• Referencing the supported tModels
• The main UDDI data structures

SOAP

• Why SOAP
• A "wire protocol" necessary for accessing distributed object services
• Vendor and/or platform-specific wire protocols hinder interoperability
• SOAP
• An Internet standard specification, the goal of which is to define a platform and vendor-neural WIRE PROTOCOL based on Internet standard protocols [HTTP & XML] to access Web Services. 
• Features
• Uses XML to package requests for services exposed by Web Services, and responds generates by Web services
• Typically uses HTTP as a transport protocol
• SOAP message
• Convey documents
• Support client-server communication

RESTful Approach

• Focus on using HTTP operations (GET, PUT, POST, DELETE) to manipulate data resources represented in XML
• No WSDL + SOAP