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Chapter 2: Basic Standards for Web Services. Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005. Highlights of this Chapter. eXtensible Markup Language (XML) Simple Object Access Protocol (SOAP)

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chapter 2 basic standards for web services
Chapter 2:Basic Standards for Web Services

Service-Oriented Computing: Semantics, Processes, Agents– Munindar P. Singh and Michael N. Huhns, Wiley, 2005

highlights of this chapter
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

standards for web services
Standards for Web Services

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

markup and metadata history
Markup and Metadata 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
    • Generally, comprehensible (easier debugging), though verbose and arcane

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

xml basics and namespaces
XML Basics and Namespaces

<?xml version="1.0"?> <!– not part of the document per se -->

<arbitrary:toptagxmlns="http://one.default.namespace/if-needed"

xmlns:arbitrary="http://wherever.it.might.be/arbit-ns"

xmlns:random="http://another.one/random-ns">

     <arbitrary:atag attr1="v1" attr2="v2">

Optional text also known as PCDATA

<arbitrary:btag attr1="v1" attr2="v2" />

</arbitrary:atag>

<random:simple_tag/> <!– abbreviate start and end -->

<random:atag attr3="v3"/> <!– compare arbitrary:atag -->

</arbitrary:toptag>

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

xml schema
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

web services basic architecture
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

basic profile bp 1 0
Basic Profile (BP 1.0)
  • The Web Services Interoperability Organization (WS-I) has specified the following Basic Profile version 1.0:
    • SOAP 1.1
    • HTTP 1.1
    • XML 1.0
    • XML Schema Parts 1 and 2
    • UDDI Version 2
    • WSDL 1.1

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

describing a service
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

soap simple object access protocol
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 bidirectional or n-party interaction

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

ex soap request
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 and below: 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

ex soap response
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

wsdl web services description language
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

wsdl data model
WSDL Data Model

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

directory services
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 characteristics and capabilities
  • 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

uddi universal description discovery and integration
UDDI: Universal Description, Discovery, and Integration
  • UDDI is 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

yellow green and white pages in uddi
Yellow, Green, and White Pages in UDDI

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

data model for uddi
Data Model for UDDI

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

wsdl uddi
WSDL  UDDI

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

chapter 2 summary
Chapter 2 Summary

The main triad of Web services standards

  • Bring together well-known ideas
    • 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 rather than programmers
  • Increasingly hidden by tools

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns