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Chapter 2: Basic Standards for Web Services

This chapter explores the fundamental standards governing web services within service-oriented computing. Key topics include eXtensible Markup Language (XML) for data representation, Simple Object Access Protocol (SOAP) for message exchange, and Web Services Description Language (WSDL) for service description. It also addresses directory services and Universal Description, Discovery, and Integration (UDDI) for service discovery. The chapter delves into the architecture of web services, highlighting the service broker's role and the interplay between service providers and requestors through protocols like SOAP.

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Chapter 2: Basic Standards for Web Services

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  1. Chapter 2:Basic Standards for Web Services Service-Oriented Computing: Semantics, Processes, Agents– Munindar P. Singh and Michael N. Huhns, Wiley, 2005

  2. Highlights of this Chapter • eXtensible Markup Language (XML) • Simple Object Access Protocol (SOAP) • Web Services Description Language (WSDL) • Directory Services • Universal Description, Discovery, and Integration (UDDI) Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  3. Standards for Web Services Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  4. Markup History • None, e.g., CSV • Ad hoc tags • SGML (Standard Generalized Markup L): complex, few reliable tools • HTML (HyperText ML): simple, unprincipled, mixes structure and display • XML (eXtensible ML): simple, yet extensible subset of SGML to capture new vocabularies • Machine processible • General, comprehensible (easier debugging), though verbose and arcane Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  5. XML Basics and Namespaces <?xml version="1.0"?> <!– not part of the document per se --> <arbitrary:elemZxmlns="http://one.default.namespace/if-needed" xmlns:arbitrary="http://wherever.it.might.be/arbit-ns" xmlns:random="http://another.one/random-ns">      <arbitrary:elemA attr1="v1" attr2="v2"> Optional text also known as PCDATA <arbitrary:elemB attr1="v1" attr2="v2" /> </arbitrary:elemA> <random:simpleElem/> <!– abbreviate start and end --> <random:elemA attr3="v3"/> <!– cfarbitrary:elemA --> </arbitrary:elemZ> Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  6. XML Schema • Grammar (data definition language) for specifying valid documents • Uses same syntax as regular XML documents: verbose and difficult to read • Provides local scoping of subelement names • Incorporates namespaces • Types • Primitive (built-in): string, integer, float, date, … • simpleType constructors: list, union • Restrictions: intervals, lengths, enumerations, regex patterns, • Flexible ordering of elements • Key and referential integrity constraints Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  7. Web Services: Basic Architecture Service Broker Registry; well-known Publish or announce (WSDL) Find or discover (UDDI) Service Provider Service Requestor Bind or invoke (SOAP) Not well-known Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  8. Basic Profile (BP 1.0) • Standard of standards: • SOAP 1.1 • HTTP 1.1 • XML 1.0 • XML Schema Parts 1 and 2 • UDDI Version 2 • WSDL 1.1 • Web Services Interoperability Organization (WS-I) • Newer versions in progress Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  9. Describing a Service • Namee.g., GetTemperature • Types of Input Parameterse.g., (String, String) • Types of Output Parameterse.g., Integer Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  10. SOAP (Simple Object Access Protocol) • Used to exchange messages via HTTP, SMTP, and SIP (Session Initiation Protocol for Internet telephony) • Originally designed for remote-procedure calls (RPC) • Works through firewalls on port 80 • Character-based, so easy to encrypt/decrypt and thus easy to secure • Inefficient due to character, not binary, data and large headers • Does not describe symmetric or multiparty interactions Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  11. Ex. SOAP Request POST /temp HTTP/1.1 Host: www.socweather.com Content-Type: text/xml; charset="utf-8" Content-Length: xxx SOAPAction: "http://www.socweather.com/temp" <!-- Above: HTTP headers and a blank line. --> <!—These comments onwards: an XML document --> <?xml version=“1.0”?> <env:Envelope xmlns:env="http://schemas.xmlsoap.org/soap/envelope/" env:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/> <env:Body> <m:GetTemp xmlns:m="http://www.socweather.com/temp.xsd"> <m:City>Honolulu</m:City> <m:When>now</m:When> </m:GetTemp> </env:Body> </env:Envelope> Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  12. Ex. SOAP Response HTTP/1.1 200 OK Content-Type: text/xml; charset="utf-8" Content-Length: xxx SOAPAction: "http://www.socweather.com/temp" <?xml version="1.0"?> <env:Envelope xmlns:env="http://schemas.xmlsoap.org/soap/envelope/" env:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/> <env:Body> <m:GetTempResponse xmlns:m="http://www.socweather.com/temp.xsd"> <m:DegreesCelsius>30</m:DegreesCelsius> </m:GetTempResponse> </env:Body> </env:Envelope> Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  13. WSDL: Web Services Description Language • Describes a programmatic interface to a Web service, including • Definitions of data types • Input and output message formats • The operations provided by the service • Network addresses • Protocol bindings Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  14. WSDL Data Model Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  15. Directory Services • Support discovery: enable applications, agents, Web service providers, Web service requestors, people, objects, and procedures to locate each other • White pages: entries found by name • Yellow pages: entries found by attributes • A basic directory might be a simple database (passive) or a broker/facilitator (active, that provides alerts and recruits participants) • UDDI: both white pages and yellow pages, but passive Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  16. UDDI: Universal Description, Discovery, and Integration • UDDI is itself a Web service that is based on SOAP and XML • UDDI registers • tModels: technical descriptions of a service’s behavior • businessEntities: describes the specifications of multiple tModels Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  17. Yellow, Green, and White Pages in UDDI Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  18. Data Model for UDDI Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  19. WSDL  UDDI Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  20. Chapter 2 Summary The main triad of Web services standards • Bring together well-known ideas from distributed computing • SOAP: object access and messaging • WSDL: based on CORBA IDL • UDDI: based on directories • Provide necessary functionality for interoperation • Are complicated in their details • Meant for tool vendors, not programmers • Increasingly hidden by tools Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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