Web Services Description Language (WSDL)

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Web Services Description Language (WSDL)

• Jason Glenn
• CDA 5937
• Process Coordination in Service and Computational
  Grids
• September 30, 2002

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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

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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.

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Web Services Model
Port
Server (Web Service)
Backend App
WS Request
Client
WS Response
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Web Services Stack
Implementation Layer
UDDI Publishing and Discovery
WSXL/.NET Web Applications
IBM WSFL/MS XLANG Workflow
WSDL/WSCL Service Descriptions
SOAP/ XML/ HTTP/SMTP Transactions/Reliability/ Messaging
Internet/ Intranet Transport Network
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Common Transfer Protocols

• HTTP
• SMTP

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HTTP

• HTTPHyperText Transfer Protocol
• Protocol commonly used to transfer information on
  the web

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SMTP

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

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MIME

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

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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

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XML vs. HTML

• XML is about describing information
• HTML is about displaying information

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XML Example
ltnotegt lttogtGeraldlt/togt ltfromgtRonlt/fromgt ltheadinggtR
eminderlt/headinggt ltbodygtDon't forget the meeting
on Friday.lt/bodygt lt/notegt
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HTML Example
ltbgtThis is a notelt/bgtltbrgt ltfont facearial
size-1gtTo Geraldlt/fontgtltbrgt lt font
faceTerminalgtFrom Ronlt/fontgtltbrgt ltbgtHeading
Reminderlt/bgtltbrgtltbrgt ltcentergtDon't forget the
meeting on Friday.lt/centergt
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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

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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

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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

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

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

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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

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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

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Example

• The following example is taken from the WSDL
  description document provided by the world wide
  web consortium. This document can be found at
  http//www.w3.org/TR/wsdl_wsdl. It is the WSDL
  definition for a simple service providing stock
  quotes.

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Example
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Expanding on WSDL

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

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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

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.NET

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

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UDDI

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

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Popular Web Services Servers

• IBM Websphere
• Not Open Source
• Trial Versions Available
• Apache Axis
• Open Source
• Free

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Useful Links

• WSDL description/specification
• http//www.w3c.org/TR/wsdl
• Apache Axis
• http//xml.apache.org/axis/
• IBM Websphere
• www.ibm.com/software/info1/websphere