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WEB SERVICES
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Agenda
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Web Service definition
Extensible Markup Language
Simple Object Access Protocol
WSDL
UDDI
Service Oriented Architecture
Web Service definition
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An open standard for
accessing componentbased applications
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Core Web services
standards include XML,
WSDL, SOAP and UDDI
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Advanced Web services
provide support for security,
transactions, reliability,
business processes, and
management
Service Standards
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XML – eXtensible Markup Language – A
uniform data representation and exchange
mechanism.
SOAP – Simple Object Access Protocol – A
standard way for communication.
UDDI – Universal Description, Discovery
and Integration specification – A mechanism
to register and locate WS based application.
WSDL – Web Services Description
Language – A standard meta language to
described the services offered.
Web Services Specifications
An Example
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Two endpoints: Client & Seller
The Client finds the Seller by searching
UDDI directory.
The Service of Seller is designed using
WSDL.
The Client gets the service by using SOAP.
The Client takes a SOAP reply defined in
WSDL.
Model
Extensible Markup Language -1
Extensible Markup Language -2
Simple Object Access Protocol
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Based on XML
A simple markup language for describing
messages between applications.
Mainly transferred via HTTP.
SOAP - Characteristics
Extensibility – security and WS-routing, ...
Neutrality - SOAP can be used over any transport
protocol such as HTTP, SMTP or even TCP.
Independency - SOAP allows for any programming
model.
SOAP - Building Blocks
 A required Envelope element that identifies
the XML document as a SOAP message.
 An optional Header element that contains
header information.
 A required Body element that contains call
and response information.
 An optional Fault element that provides
information about errors that occurred while
processing the message.
SOAP – Request
<?xml version="1.0"?>
<soap:Envelope
xmlns:soap="http://www.w3.org/2001/12/soap-envelope"
soap:encodingStyle=http://www.w3.org/2001/12/soap-encoding”>
<soap:Body xmlns:m="http://www.Bazaar.org/Bazaar">
<m:GetBazaarPrice>
<m:Type>Shirt</m:Type>
</m:GetBazaarPrice>
</soap:Body>
</soap:Envelope>
Soap - Response
<?xml version="1.0"?>
<soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soapenvelope"
soap:encodingStyle="http://www.w3.org/2001/12/soapencoding">
<soap:Body xmlns:m="http://www.Bazaar.org/Bazaar">
<m:GetBazaarPriceResponse>
<m:Price>34.5</m:Price>
</m:GetBazaarPriceResponse>
</soap:Body>
</soap:Envelope>
WSDL
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Stands for Web Services Description Language.
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Based on XML.
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WSDL specifies what a request message and a
response message must contain. A contract between
the XML Web service and the client ...
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In addition to describing message contents, it defines
where the service is available and what
communications protocol can be used to invoke it.
WSDL - Primary Elements
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PortType - Defines the abstract interface to the Service.
Associated with one or more operations.
Message - Defines the information exchanged at the time
an operation is executed (input and output). Made of one
or more parts.
Part – Elemental piece of information in a message (an
individual parameter or return value)
Types - The data types used by the web service.
Binding - The communication protocols used by the web
service
Port – Identifies the actual location of the service (a URL,
a Java class, etc..)
WSDL - Example
<message name="GetBazaarPriceRequest">
<part name=“" type="xs:string"/>
</message>
<message name="GetBazaarPriceResponse">
<part name="value" type="xs:string"/>
</message>
<portType name=“BazaarsRates">
<operation name=“GetBazaarPrice">
<input message=“GetBazaarPriceRequest"/>
<output message=“GetBazaarPriceResponse"/>
</operation>
</portType>
WSDL & OO
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Example: a service implemented by a Java
class could define one or more operations.
Operations would map to individual Java
methods, implemented by the class.
Messages would map to the return types of
the methods, or to their parameter list.
Parts would map to the elemental data in
the parameter list or the return values.
UDDI
Service Oriented Architecture
Service Oriented Architecture -2
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An approach for building distributed systems that deliver
application functionality as services to either end-user
applications or other services
The minimum requirements of an SOA are:
– Services
– Enterprise service bus (ESB)
– Service directory: An organization-level WSDL repository
– Internet gateway: Enables internal services to be exposed to the
Internet
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Value of SOA
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Build once, use often
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Interface by contract
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One place to make one change
Lower development, operations and maintenance costs
Loosely couples requestor and provider so each can vary
independently
Integration is explicitly defined and so better understood,
at the application and Enterprise level
Simplified, agreed, defined data and process flows