Chapter 2: Basic Standards for Web Services

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• Chapter 2Basic Standards for Web Services

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

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Standards for Web Services
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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

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XML Basics and Namespaces

• lt?xml version"1.0"?gt lt! not part of the
  document per se --gt
• ltarbitrarytoptag xmlns"http//one.default.namesp
  ace/if-needed"
• xmlnsarbitrary"http//wherever.it.might.be/arb
  it-ns"
•       xmlnsrandom"http//another.one/random-ns"gt
  
•      ltarbitraryatag attr1"v1" attr2"v2"gt
• Optional text also known as PCDATA
• ltarbitrarybtag attr1"v1" attr2"v2" /gt
• lt/arbitraryataggt
• ltrandomsimple_tag/gt lt! abbreviate start and end
  --gt
• ltrandomatag attr3"v3"/gt lt! compare
  arbitraryatag --gt
• lt/arbitrarytoptaggt

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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

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Web Services Basic Architecture
Service Broker
Registry well-known
Find or discover (UDDI)
Publish or announce (WSDL)
Service Provider
Service Requestor
Bind or invoke (SOAP)
Not well-known
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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

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Describing a Service

• Namee.g., GetTemperature
• Types of Input Parameterse.g., (String, String)
• Types of Output Parameterse.g., Integer

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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

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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"
• lt!-- Above HTTP headers and a blank line. --gt
• lt!These comments and below an XML document --gt
• lt?xml version1.0?gt
• ltenvEnvelope
• xmlnsenv"http//schemas.xmlsoap.org/soap/envelo
  pe/"
• envencodingStyle"http//schemas.xmlsoap.org/soa
  p/encoding/"/gt
• ltenvBodygt
• ltmGetTemp xmlnsm"http//www.socweather.com/te
  mp.xsd"gt
• ltmCitygtHonolulult/mCitygt
• ltmWhengtnowlt/mWhengt
• lt/mGetTempgt
• lt/envBodygt
• lt/envEnvelopegt

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Ex. SOAP Response

• HTTP/1.1 200 OK
• Content-Type text/xml charset"utf-8"
• Content-Length xxx
• SOAPAction "http//www.socweather.com/temp"
• lt?xml version"1.0"?gt
• ltenvEnvelope xmlnsenv"http//schemas.xmlsoap.or
  g/soap/envelope/"
• envencodingStyle"http//schemas.xmlsoap.org/
  soap/encoding/"/gt
• ltenvBodygt
• ltmGetTempResponse
  xmlnsm"http//www.socweather.com/temp.xsd"gt
• ltmDegreesCelsiusgt30lt/mDegreesCelsiusgt
• lt/mGetTempResponsegt
• lt/envBodygt
• lt/envEnvelopegt

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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

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WSDL Data Model
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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

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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 services
  behavior
• businessEntities describes the specifications of
  multiple tModels

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Yellow, Green, and White Pages in UDDI
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Data Model for UDDI
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WSDL ?? UDDI
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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