Web Services Description Language (WSDL) Jason Glenn CDA 5937 Process Coordination in Service and Computational Grids September 30, 2002

Outline What is a web service? Web Services Model Web Services Stack Lower level WS protocols What is WSDL? Explain contents of WSDL documents Higher level WS and WS-related applications

What is a Web Service? Self-contained, modular web application that can be published, located, and invoked across the Web. Can perform functions of varying complexities Once deployed, other applications (and other Web services) can discover and invoke the deployed service.

Web Services Model Server (Web Service) Client WS Request WS Response Port Backend App

Web Services Stack ImplementationLayer UDDIPublishing and Discovery WSXL/.NETWeb Applications IBM WSFL/MS XLANGWorkflow WSDL/WSCLService Descriptions SOAP/ XML/ HTTP/SMTPTransactions/Reliability/ Messaging Internet/ IntranetTransport Network

Common Transfer Protocols HTTP SMTP

HTTP HTTP=HyperText Transfer Protocol Protocol commonly used to transfer information on the web

SMTP SMTP = Simple Mail Transfer Protocol Protocol used to exchange information between mail servers

MIME MIME = Multipurpose Internet Mail Extensions Internet standard that specifies how messages are formatted for exchange between different systems flexible format

Review of XML XML = EXtensible Markup Language A markup language like HTML (HyperText Markup Language) Designed to describe data Tags are not predefined Uses a Document Type Definition (DTD) or an XML Schema to describe the data Designed to be self-descriptive

XML vs. HTML XML is about describing information HTML is about displaying information

XML Example Gerald Ron Reminder Don't forget the meeting on Friday.

HTML Example This is a note To: Gerald From: Ron Heading: Reminder Don't forget the meeting on Friday.

XML Documents Not quite the same as HTML documents Can be seen independently of files (one document can contain many files; one file can contain many documents) Concerned more with logical structure than physical structure

XML Namespaces An XML namespace is a collection of names, which are used in XML documents as element types and attribute names WSDL document elements belong to WSDL namespace

SOAP (Simple Object Access Protocol ) a lightweight and simple XML-based protocol that is designed to exchange structured and typed information on the Web Standard way of representing remote procedure calls and responses Standard to encapsulate messages between Web service clients and servers SOAP Envelope

SOAP

SOAP Envelopes Server (Web Service) Client WS Response Port Backend App WS Request Soap Envelope/HTTP

What is WSDL? Web Services Description Language An XML format for describing network services as a set of endpoints operating on messages.

Characteristics of WSDL Operations and messages are described abstractly Endpoints defined by binding concrete network protocol and message format to abstract operations and messages Can describe any endpoint regardless of the underlying network protocol or message format

WSDL Document Elements Types – a container for data type definitions using some type system Message – an abstract, typed definition of the data being communicated Operation – an abstract description of an action supported by the service Port Type – an abstract set of operations supported by one or more endpoints Binding – a concrete protocol and data format specification for a particular port type Port – a single endpoint defined as a combination of a binding and a network address Service – a collection of related endpoints

Example The following example is taken from the WSDL description document provided by the world wide web consortium. This document can be found at It is the WSDL definition for a simple service providing stock quotes.

Example

Expanding on WSDL WSXL IBM web services component model based on open standards.NET Microsoft web services component model UDDI Web Service Registry

WSXL Goals enable businesses to deliver interactive Web applications through multiple distribution channels enable new services or applications to be created by leveraging other interactive applications across the Web

.NET Goal Applications constructed from multiple Web services that work together to provide data and services for the application

UDDI Universal Description, Discovery and Integration Platform-independent, open framework for describing and discovering web services using the Internet UDDI Registries

Popular Web Services Servers IBM Websphere Not Open Source Trial Versions Available Apache Axis Open Source Free

Useful Links WSDL description/specification Apache Axis IBM Websphere