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Basic Standards for Web ServicesCS 696 – Services Computing

Fall 2008

Chapter 2: 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

BPEL4WSOWL-S Service

Model

ebXMLCPA

Process and workfloworchestrations

QoS: Servicedescriptions 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 ServiceGrounding

OWL-S ServiceProfile

BTP

BPML

Discovery

Messaging

Transport

QoS: Conversations

QoS: Choreography

QoS: Transactions

Encoding

WS-Policy

WS-Security

WS-ReliableMessaging

PSL

RDF

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XML Web Service Foundation

Open and with broad industry support

Publish, Find, Use Services UDDI

Service Interactions SOAP

Universal Data Format XML

Description Language WSDL

Ubiquitous Communications TCP/IP, HTTP, SMTP, SIP, Reliable messaging

Security (authentication and authorization) WS-Security, SAML

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Markup History

None, as in comma separated values 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 Comprehensible to people: easier debugging

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Brief Introduction to XML

Basics Parsing Storage Transformations

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XML Basics and Namespaces

<?xml version="1.0"?> <!– not part of the document per se <arbitrary:toptag xmlns=“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/><random:atag attr3=“v3”/> <!–compare with arbitrary:atag

</arbitrary:toptag>

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XML Example

<?xml version="1.0"? Encoding=‘UTF-8’?><temperature scale=“Celsius”>     <value>25</value>

<accuracy>2</accuracy> <ambience condition=“shade”/>

</temperature>

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XML Example

<?xml version="1.0"?><temperature accuracy=“2” scale=“Celsius”>     25

<ambience condition=“shade”/></temperature>

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HTML Example of same data<TABLE BORDER=1> <TR>    <TH>Value</TH>    <TH>Accuracy</TH>    <TH>Scale</TH>    <TH>Ambience Condition</TH> </TR> <TR>

<TD>25</TD> <TD>2</TD> <TD>Celsius</TD> <TD>Shade</TD>

</TR></TABLE>

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XML Query Languages

XPath XPointer XSLT XQuery

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XPath

Model XML documents as trees with nodes Elements Attributes Text (PCDATA) Comments Root node: above root of document

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XPath

Parent in XPath is like parent as traditionally in computer science

Child in XPath is confusing: An attribute is not the child of its

parent Makes a difference for certain kinds of

recursion (e.g., apply-templates discussed in XSLT)

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XPath Paths

Leading /: root /: indicates walking down a tree .:current node ..:parent node @attr: to access values for the

given attribute text() comment()

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XPath Navigation

Select children according to position, e.g., [j], where j could be 1 … last()

Descendant-or-self operator, // .//elem finds all elems under the

current //elem finds all elems in the document

Wildcard, *: @*: finds all attribute values

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XPath Queries

Incorporate selection conditions in XPath Attributes: //Song[@genre=“jazz”] Elements: //Song[starts-with(.//group, “Led”)] Existence of attribute: //Song[@genre] Existence of subelement: //Song[group] Boolean operators: and, not, or Set operator: union (|); none others Arithmetic operators: >, <, … String functions: contains(), concat(), length(), Aggregates: sum(), count()

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XPointer

Combines XPath with URLs URL to get to a document; XPath to

walk down the document Can be used to formulate queries,

e.g., Song-URL#xpointer(//

Song[@genre=“jazz”])

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XSLT

A functional programming language

A stylesheet specifies transformations on a document<?xml version=“1.0”?><?xml-stylesheet type=“text/xsl”

href=“URL-to-dot-xsl”?> <!– the sheet to use <main-tag>…</main-tag>

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XSLT Stylesheets

Use the XSLT namespace, conventionally abbreviated as xsl Includes primitives: Copy-of <for-each select=“…”> <if test=“…”> <choose >

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XML file referencing XSL stylesheet

<?xml version=“1.0”?><?xml:stylesheet type=“text/xsl” href=“TempTable.xsl”?> <TempCollection>    <temperature scale=“Celsius”>     <value>25</value>     <accuracy>2</accuracy>    </temperature> <temperature scale=“Kelvin”>     <value>123</value>     <accuracy>5</accuracy>    </temperature> <temperature scale=“Fahrenheit”>     <value>32</value>     <accuracy>1</accuracy>    </temperature> </TempCollection>

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Stylesheet (TempTable.xsl)

<xsl:Stylesheet version=“1.0” xmlns:xsl=“http://www.w3.org/1999/XSL/Transform”> <xsl:template match=“/”> <HTML> <BODY> <xsl:apply-templates /> </BODY> </HTML> </xsl:template> <xsl:template match=“TempCollection”> <TABLE BORDER=“2”> <TR> <TH>Value</TH>     <TH>Accuracy</TH>     <TH>Scale</TH> </TR> <xsl:apply-templates/> </TABLE> </xsl:template> <xsl:template match=“temperature”> <TR> <TD><xsl:value-of select=“value”/></TD> <TD><xsl:value-of select=“accuracy”/></TD> <TD><xsl:value-of select=“@scale”/></TD> </TR> </xsl:template></xsl:stylesheet>

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XSLT Templates: 1

A pattern to specify where a given transform should apply This match only works on the root:<xsl:template match=“/”>…</xsl:template>

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XSLT Templates: 2

Can be applied recursively on the children via

<xsl:apply-templates/>

By default, if no other template matches, recursively apply to children of current node (ignores attributes) and to root:

<xsl:template match=“*|/”><xsl:apply-templates/>

</xsl:template>

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Parsing and Validating An XML document maps to a parse tree.

Each tag ends once: nesting structure (one root) Each attribute occurs at most once; quoted string

Well-formed XML documents can be parsed Applications have an explicit or implicit syntax

for their particular XML-based tags If explicit, may be expressed in DTDs and XML

Schemas Best referred to definitions elsewhere XML Schemas, expressed in XML, are superior to DTDs

When docs are produced by external components, they should be validated

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DTD (Document Type Definition) Example

<?xml version="1.0"? Encoding=‘UTF-8’?><TempCollection> <temperature scale=“Celsius”>     <value>25</value>

<accuracy>2</accuracy> <ambience condition=“shade”/> </temperature></TempCollection>

<?xml encoding="UTF-8"?><!ELEMENT TempCollection (temperature)+><!ELEMENT temperature (value, accuracy,ambience)><!ELEMENT value (#PCDATA)><!ELEMENT accuracy (#PCDATA)><!ELEMENT ambience (#EMPTY)><!ATTLIST temperature scale (Celsius|Fahrenheit|Kelvin)

#REQUIRED><!ATTLIST ambience condition CDATA “shade”>

#PCDATA – Parsed Character data, can contain markup CDATA – Character data, is not parsed for markup

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XML Schema A data definition language for XML: defines

a notion of schema validity; helps us define desired grammars for documents Same syntax as regular XML documents Local scoping of subelement names Incorporates namespaces Types

Primitive (built-in): string, ID, IDREF, 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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XML Schema example

<?xml version=“1.0”?><xsd:schema xmlns:xsd=“http://www.w3.org/2001/XMLSchema” … ><xsd:element name="TempCollection"> <xsd:complexType> <xsd:sequence> <xsd:element ref="temperature" minOccurs="1" maxOccurs="unbounded"/> </xsd:sequence> </xsd:complexType> </xsd:element>

<xsd:element name="temperature"> <xsd:complexType> <xsd:sequence> <xsd:element ref="value" minOccurs="1" maxOccurs="1"/> <xsd:element ref="accuracy" minOccurs="1" maxOccurs="1"/> </xsd:sequence> <xsd:attributeGroup ref="TempAttributes"/> </xsd:complexType> </xsd:element>

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XML Schema example

  <xsd:attributeGroup name="TempAttributes">

<xsd:attribute name="scale" use="required"> <xsd:simpleType> <xsd:restriction base="xsd:string"> <xsd:pattern value="Celsius"/> <xsd:pattern value="Fahrenheit"/> <xsd:pattern value="Kelvin"/> </xsd:restriction> </xsd:simpleType> </xsd:attribute> </xsd:attributeGroup> <xsd:element name="value" type="xsd:integer"/> <xsd:element name="accuracy" type="xsd:nonNegativeInteger"/>

</xsd:schema>

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XML Schema: complexType

Specifies types of elements with structure: Must use a compositor if > 1

subelements Subelements with types Min and max occurrences (default 1)

of subelements

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XML Schema: Compositors

Sequence: ordered Can occur within other compositors Allows varying min and max occurrence

All: unordered Must occur directly below root element Max occurrence of each element is 1

Choice: exclusive or Can occur within other compositors

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XML Schema: Key Namespaces

http://www.w3.org/2001/XMLSchema Conventional prefix: xsd Terms for defining schemas: schema, element,

attribute, … The tag schema has an attribute

targetNamespace http://www.w3.org/2001/XMLSchema-

instance Conventional prefix: xsi Terms for use in instances: schemaLocation, null

targetNamespace: user-defined

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XML Schema Instance Doc

<Music xmlns=http://a.b.c/Muse

xmlns:xsi=“the standard-xsi”xsi:schemaLocation=“a-schema-as-

a-URI a-schema-location-as-a-URL”>

…</Music>

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Creating Schema Docs: 1

<schema xmlns=“the-standard-xsd”targetNamespace=“the-

target”> <include schemaLocation=“part-

one.xsd”/> <include schemaLocation=“part-

two.xsd”/></schema>

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Creating Schema Docs: 2

Use imports instead of include Specify namespaces from which

schemas are to be imported Location of schemas not required and

may be ignored if provided

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Document Object Model (DOM)

Basis for parsing XML, which provides a node-labeled tree in its API Conceptually simple: traverse by requesting

tag, its attribute values, and its children Processing program reflects document

structure Can edit documents Inefficient for large documents: parses them

first entirely to build the tree even if a tiny part is needed

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DOM Example [Simeoni 2003]

Element s = d.getDocumentElement();NodeList l =

s.getElementsByTagName(“member”); Element m = (Element) l.item(0);int code = m.getAttribute(“code”);NodeList kids = m.getChildNodes();Node kid = kids.item(0);String tagName =

((Element)kid).getTagName();…

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Simple API for XML (SAX)

Parser generates a sequence of events: startElement, endElement, …

Programmer implements these as callbacks More control for the programmer

Processing program does not reflect document structure

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SAX Example [Simeoni 2003]

class MemberProcess extends DefaultHandler {public void startElement (String uri, String n,

String qName, Attributes attrs) {if (n.equals(“member”)) code = attrs.getValue(“code”);if (n.equals(“project”)) inProject = true;buffer.reset(); }

public void endElement (String uri, String n, String qName) {if (n.equals(“project”)) inProject = false;if (n.equals(“member”) && !inProject)

name = buffer.toString().trim(); } }

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Programming with XML

Current approaches concentrate on structure but ignore meaning Difficult to construct and maintain Treat everything as a string Inadequate type checking can hide

errors Emerging approaches (e.g., JAXB)

provide superior binding from XML to programming languages Primitives such as unmarshal to

materialize an object from XML

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Uses of XML

Exchanging information across software components

Storing information in nonproprietary format

XML documents represent structured descriptions: Products, services, catalogs Contracts Queries, requests, invocations (as in SOAP)

Data-centric versus document-centric (irregular, heterogeneous data, depend on entire doc for app-specific meaning) views

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Data-Centric View<relation>

<tuple><attr1>V11</attr1>… <attrn>V1n</attrn></tuple>…<tuple><attr1>Vm1</attr1>… <attrn>Vmn</attrn></tuple>

</relation> Extract and store into DB via

mapping to DB model Regular, homogeneous tags May be expensive if repeatedly

parsed and instantiated

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Document-Centric View

Storing docs in DBs Use character large objects (clobs)

within DB Store paths to external files containing

docs Combine with some structured

elements with search conditions for both structured elements and unstructured clobs or files

Heterogeneity also complicates mappings to traditional typed OO programming languages

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Directions Limitations of XML

Doesn’t represent meaning Enables multiple representations for the

same information; transform if models known

Trends: sophisticated approaches for Querying and manipulating XML, e.g.,

XSLT Binding to PLs and DBs Semantics, e.g., RDF, DAML, OWL, …

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XML Summary

XML enables information sharing XML is well established

Several aspects are worked out Lots of tools Works with databases and

programming languages XML provides a useful substrate for

service-oriented computing

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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)

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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Interactions

Via MethodsVia Methods Via MessagesVia Messages

Purchasing()Purchasing()

CatalogService()CatalogService()

Order()Order()

invokeinvoke

invokeinvoke

catalogcatalog

confirmation #confirmation #

Dell Purchasing Intel Sales

SubmitPO

AckPO

SubmitASN

SubmitInvoice

SubmitPayment

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

<!-- The above are HTTP headers --><?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"> <DegreesCelsius>30</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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WSDL Example

<?xml version="1.0"?><!-- the root element, wsdl:definitions, defines a set of --><!-- related services --><wsdl:definitions name="Temperature" targetNamespace="http://www.socweather.com/schema" xmlns:ts="http://www.socweather.com/TempSvc.wsdl"

xmlns:tsxsd="http://schemas.socweather.com/TempSvc.xsd"

xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/">

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WSDL Example

<!-- wsdl:types encapsulates schema definitions of communication types -->

<wsdl:types> <!-- all type declarations are expressed in xsd --> <xsd:schema targetNamespace="http://namespaces.socweather.com" xmlns:xsd="http://www.w3.org/1999/XMLSchema"> <!-- xsd def: GetTemp [City string, When string] --> <xsd:element name="GetTemp"> <xsd:complexType> <xsd:sequence> <xsd:element name="City" type="string"/> <xsd:element name="When" type="string"/> </xsd:sequence> </xsd:complexType> </xsd:element>

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WSDL Example <!-- xsd def: GetTempResponse [DegreesCelsius integer] --> <xsd:element name="GetTempResponse"> <xsd:complexType> <xsd:all> <xsd:element name="DegreesCelsius" type="integer"/> </xsd:all> </xsd:complexType> </xsd:element>

<!-- xsd def: GetTempFault [errorMessage string] --> <xsd:element name="GetTempFault"> <xsd:complexType> <xsd:all> <xsd:element name="errorMessage" type="string"/> </xsd:all> </xsd:complexType> </xsd:element> </xsd:schema></wsdl:types>

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WSDL Example<!-- wsdl:message elements describe potential transactions -->

<!-- request GetTempRequest is of type GetTemp --><wsdl:message name="GetTempRequest"> <wsdl:part name="body" element="tsxsd:GetTemp"/></wsdl:message>

<!-- response GetTempResponse is of type GetTempResponse --><wsdl:message name="GetTempResponse"> <wsdl:part name="body" element="tsxsd:GetTempResponse"/></wsdl:message>

<!-- wsdl:portType describes messages in an operation --><wsdl:portType name="GetTempPortType"> <wsdl:operation name="GetTemp"> <!-- The order of input and output is significant; <!-- input preceding output indicates the request-response operation type --> <wsdl:input message="ts:GetTempRequest"/> <wsdl:output message="ts:GetTempResponse"/> <wsdl:fault message="ts:GetTempFault"/> </wsdl:operation> </wsdl:portType>

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WSDL Example<!-- wsdl:binding states a serialization protocol for this service --><wsdl:binding name="TempSvcSoapBinding" type="ts:GetTempPortType">

<!-- leverage off soap:binding document style --> <soap:binding style="document" transport="http://schemas.xmlsoap.org/soap/http"/> <!-- semi-opaque container of network transport details classed by soap:binding above

--> <wsdl:operation name="GetTemp">

<!-- further specify that the messages in the wsdl:operation "GetTemp" use SOAP -->

<soap:operation soapAction="http://www.socweather.com/TempSvc"/> <wsdl:input> <soap:body use="literal"

namespace="http://schemas.socweather.com/TempSvc.xsd"/> </wsdl:input> <wsdl:output> <soap:body use="literal"

namespace="http://schemas.socweather.com/TempSvc.xsd"/> </wsdl:output> <wsdl:fault> <soap:body use="literal"

namespace="http://schemas.socweather.com/TempSvc.xsd"/> </wsdl:fault> </wsdl:operation></wsdl:binding>

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WSDL Example

<wsdl:service name="TemperatureService">

<wsdl:documentation>socweather.com temperature service </wsdl:documentation>

<!-- connect it to the binding "TempSvcSoapBinding" above --> <wsdl:port name="GetTempPort"

binding="ts:TempSvcSoapBinding"> <!-- give the binding a network address --> <soap:address

location="http://www.socweather.com/TempSvc"/> </wsdl:port>

</wsdl:service>

</wsdl:definitions>

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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