LN 7 Web Services

Web Services

A new breed of Web application. They are self-contained, self-describing, modular applications that can be published, located, and invoked across the Web.

Six key components of Web Services

• Self-contained

• Self-describing

• Modular applications

• Published

• Located

• Invoked across the web

Why Web services

• Web Services are standards-based

• Vendor-neutral

• Language-agnostic

• They have been designed to leverage the service-centric, asynchronous nature of the Internet

Web Service Architectural Perspective

A web service is essentially a standards-based façade, or wrapper for accessing non-standardized middleware components

Web Service Invocation process:

• Client queries a UDDI registry node

• Server returns a list of records matching request

• Client identifies a specific service of interest

• Server binds client to the service so client can invoke service methods

Types of Web Services:

• Component Wrapper

• B2B facilitator

• Componentised E-services

• Dynamic Business Enabler

Software Architecture today:

• Tightly coupled

• Long development cycles

• Expensive

Web Services characteristics

• Loosely Coupled

• Coarse-Grained

• Asynchronous

Reasons Java is a good implementation choice for Web services:

• polymorphic support facilitates type-based selection of web services at runtime

• interface support cleanly decouples service architecture

• interface and encapsulation support facilitate good OO design techniques for exposing service methods

• inheritance allows for rapid creation of new services based on generic templates

Web Services Industries:

• Microsoft .NET

• IBM Dynamic E-Business

• Sun ONE

• MindElectric Glue

Web Services Description Language (WSDL)

XML-formatted language that defines the ways you can contact a web service and describes the message formats you should use

What WSDL does

• Makes a neutral declaration of the existence of one or more services

• Describes the way a client can interact with those services

WSDL Elements Service Layers

1. data types that the service operates on

2. message types the service can receive/send

3. how these messages combine into operations

4. what protocols the service will bind to

5. WSDL ports (operation + protocol)

6. A service on a given port

Universal Description, Discovery, and Integration (UDDI) serves as three things

• Service Provider: provides & publishes e-business web services

• Service Registry: a SOAP-activated web service yellow pages

• Service Requester: finds required services and binds client to those services

Web Service Invocation

• Client queries a UDDI registry node

• Server returns a list of records matching request

• Client identifies a specific service of interest

• Server binds client to the service so client can invoke service methods

3 Core UDDI Elements

1. Business Services

2. Binding Templates

3. Tmodels