Chapter 2:Basic Standards for Web Services

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

Chapter 2 2Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

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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Michael Huhns

Standards for Web Services

BPEL4WSOWL-S Service

Model

ebXMLCPA

Process and workflow orchestrations

QoS: Service descriptions and bindings

Contracts andagreements

XLANG

WSCL

WSDLebXML

CPP

ebXMLBPSS

XML, DTD, and XML Schema

HTTP, FTP, SMTP, SIP, etc.

SOAPebXML

messaging

OWL

UDDIebXML

Registries

WSCLWSCI

WS-Coordination

WS-AtomicTransaction and WS-BusinessActivity

OWL-S Service Grounding

OWL-S Service Profile

BTP

BPML

Discovery (not selection)

Messaging

Transport

QoS: Conversations

QoS: Choreography

QoS: Transactions

Encoding

WS-Policy

WS-Security

WS-Reliable Messaging

PSL

RDF

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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 Generall, comprehensible (easier debugging),

though verbose and arcane

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XML Basics and Namespaces

<?xml version="1.0"?> <!– not part of the document per se --><arbitrary:elemZ xmlns="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"/> <!– cf arbitrary:elemA -->

</arbitrary:elemZ>

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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

ServiceBroker

ServiceProvider

ServiceRequesto

r

Bind or invoke(SOAP)

Find or discover(UDDI)

Publish or announce(WSDL)

Registry; well-known

Not well-known

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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

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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 symmetric or multiparty

interactions

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Ex. SOAP Request

POST /temp HTTP/1.1Host: www.socweather.comContent-Type: text/xml; charset="utf-8"Content-Length: xxxSOAPAction: "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>

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Ex. SOAP Response

HTTP/1.1 200 OKContent-Type: text/xml; charset="utf-8"Content-Length: xxxSOAPAction: "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>

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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

definitions targetNamespace=thisNamespace xmins:tns=thisNamespace

types message name=in message name=out

portType name=foo operation input message=tns:in output message=tns:out

binding name=foobar type=tns:foo [binding information]

service name=foobar Service

Port name=foobarPort binding=tns:foobar [endpoint information]

Types contains data type definitionsMessages consist of one or more parts

A portType describes an abstract setof operations

A binding describes a concrete set offormats and protocols for the fooportTypes

A port describes an implementationof the foobar binding

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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 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

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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

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Yellow, Green, and White Pages in UDDI

-businessKey : string(idl)-name : string(idl)-description : string(idl)-URL : string(idl)-contacts : contact-businessServices : businessService-identifierBag : keyedReference-categoryBag : keyedReference

businessEntity

1

*

-tModelKey : string(idl)-keyName : string(idl)-keyValue : string(idl)

keyedReference

-serviceKey : string(idl)-tModelKey : string(idl)-name : string(idl)-description : string(idl)-bindingTemplates

businessService

-phone : string(idl)-address : string(idl)

contact

businessEntity: Information about theparty who publishes information about

a service

businessService: Descriptiveinformation about a particular family of

technical services

bindingTemplate: Technicalinformation about a service entry point

and implementation specs

tModel: Descriptions of specificationsfor services or value sets. Basis for

technical fingerprints

businessEntities containbusinessServices

businessServices containbindingTemplates

bindingTemplates contain referencesto tModels. These references

designate the interface specificationsfor a service

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Data Model for UDDI

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WSDL UDDI

<import>

<port>

<port>

BusinessEntity

BusinessService

BindingTemplate

BindingTemplate

Service Implementation

UDDI

<service>

Service Interface

<types>

<message>

<portType>

<binding>

tModel

WSDL

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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