Web service architecture

Table of Contents
• What’s Web Service?
• Web Service Model
• Architecture Overview
– SOAP
– WSDL
– UDDI
• Conclusion

What’s Web Service?
• “Software application identified by a URI, whose interfaces and bindings are
capable of being defined, described, and discovered as XML artifacts” – W3C Web
Services Architecture Requirements, Oct. 2002
• “Programmable application logic accessible using Standard Internet Protocols…” –
Microsoft
• “An interface that describes a collection of operations that are network accessible
through standardized XML messaging …” – IBM
• “Software components that can be spontaneously discovered, combined, and
recombined to provide a solution to the user’s problem/request … “ - SUN

Web Services: The Next Horizon for e-
business
• Allow companies to reduce the cost of doing e-business, to
deploy solutions faster
– Need a common program-to-program communications model
• Allow heterogeneous applications to be integrated more
rapidly, easily and less expensively
• Facilitate deploying and providing access to business
functions over the Web

Sun J2EE MS .NET Platform
CORBA

Web Service Model (2/3)
• Roles in Web Service architecture
– Service provider
• Owner of the service
• Platform that hosts access to the service
– Service requestor
• Business that requires certain functions to be satisfied
• Application looking for and invoking an interaction with
a service
– Service registry
• Searchable registry of service descriptions where
service providers publish their service descriptions

Web Service Model (3/3)
• Operations in a Web Service Architecture
– Publish
• Service descriptions need to be published in order for
service requestor to find them
– Find
• Service requestor retrieves a service description
directly or queries the service registry for the service
required
– Bind
• Service requestor invokes or initiates an interaction
with the service at runtime

SOAP: Simple Object
Access Protocol
• What is SOAP?
– SOAP is a communication protocol
– SOAP is for communication between applications
– SOAP is a format for sending messages
– SOAP is designed to communicate via Internet
– SOAP is platform independent
– SOAP is language independent
– SOAP is based on XML
– SOAP is simple and extensible
– SOAP will be developed as a W3C standard

SOAP: Simple Object
Access Protocol
• SOAP 1.0: Microsoft, Userland, DevelopMentor
– Specific to COM and HTTP
• SOAP 1.1: includes contributions from IBM and Lotus
– Substitutable transport binding (not just HTTP)
– Substitutable language binding (e.g. Java)
– Substitutable data encoding
– Completely vendor-neutral
– Independent of: programming language, object model, operating
system, or platform
• SOAP 1.2: current working draft from w3.org “XML Protocol”
working group

SOAP Message Structure
• Request and Response messages
– Request invokes a method on a remote
object
– Response returns result of running the
method
• SOAP specification defines an “envelop”
– “envelop” wraps the message itself
– Message is a different vocabulary
– Namespace prefix is used to distinguish the
two parts
Application-specific
message vocabulary
SOAP Envelop
vocabulary

SOAP Request Message
<?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.stock.org/stock">
</soap:Body>
</soap:Envelope>
<m:GetStockPrice>
<m:StockName>IBM</m:StockName>
</m:GetStockPrice>
SOAP Envelope
Message
SOAP Envelope
Namespace
Message
Namespace

SOAP Response Message
<?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.stock.org/stock">
</soap:Body>
</soap:Envelope>
<m:GetStockPriceResponse>
<m:Price>34.5</m:Price>
</m:GetStockPriceResponse>
SOAP Envelope
Message
Result
returned in
Body

• SOAP hides the technical choices and implementation
details from both parties
Simple standard XML Message

Why SOAP?
• Other distributed technologies failed on the Internet
– Unix RPC – requires binary-compatible Unix implementations at
each endpoint
– CORBA – requires compatible ORBs
– RMI – requires Java at each endpoint
– DCOM – requires Windows at each endpoint
• SOAP is the platform-neutral choice
– Simply an XML wire format
– Places no restrictions on the endpoint implementation technology
choices

SOAP Usage Models
• RPC-like message exchange
– Request message bundles up method name and parameters
– Response message contains method return values
– However, it isn’t required by SOAP
• SOAP specification allows any kind of body content
– Can be XML documents of any type
– Example:
• Send a purchase order document to the inbox of B2B partner
• Expect to receive shipping and exceptions report as response

Web Services Description Language
• What is WSDL?
– WSDL is written in XML
– WSDL is an XML document
– WSDL is used to describe Web services
– WSDL is also used to locate Web services
– WSDL is not yet a W3C standard
• Operational information about the service
– Location of the service
– Service interface
– Implementation details for the service interface

WSDL Document Structure (1/2)
• <portType> element
– Defines a web service, the operations that can be
performed, and the messages that are involved
• <message> element
– Defines the data elements of an operation
– consists of one or more parts.
– The parts can be compared to the parameters of a
function call in a traditional programming
language

WSDL Document Structure (2/2)
• <types> element
– Defines the data type that are used by the web
service
– For maximum platform neutrality, WSDL uses
XML Schema syntax to define data types
• <binding> element
– Defines the message format and communication
protocols used by the web service

<message name="getTermRequest">
<part name="term" type="xs:string"/>
</message>
<message name="getTermResponse">
<part name="value" type="xs:string"/>
</message>
<portType name="glossaryTerms">
<operation name="getTerm">
<input message="getTermRequest"/>
<output message="getTermResponse"/>
</operation>
</portType>
WSDL Example

<message name="getTermRequest">
<part name="term" type="xs:string"/>
</message>
<message name="getTermResponse">
<part name="value" type="xs:string"/>
</message>
<portType name="glossaryTerms">
<operation name="getTerm">
<input message="getTermRequest"/>
<output message="getTermResponse"/>
</operation>
</portType>
<binding type="glossaryTerms" name="b1">
<soap:binding style="document"
transport="http://schemas.xmlsoap.org/soap/http" />
<operation>
<soap:operation
soapAction="http://example.com/getTerm"/>
<input>
<soap:body use="literal"/>
</input>
<output>
<soap:body use="literal"/>
</output>
</operation>
</binding> Binding to SOAP

Universal Description, Discovery
and Integration (UDDI)
• What is UDDI?
– Directory service where businesses can register and search for Web
services
• Directory for storing information about web services
• Directory of web service interfaces described by WSDL
– UDDI communicates via SOAP
• What is UDDI Based On?
– Uses W3C Internet standards such as XML, HTTP, and DNS protocols
– UDDI uses WSDL to describe interfaces to web services

UDDI Roles and Operations
• Service Registry
– Provides support for publishing and
locating services
– Like telephone yellow pages
• Service Provider
– Provides e-business services
– Publishes these services through a
registry
• Service requestor
– Finds required services via the
Service Broker
– Binds to services via Service
Provider

UDDI Benefits
• Making it possible to discover the right
business from the millions currently online
• Defining how to enable commerce once the
preferred business is discovered
• Reaching new customers and increasing
access to current customers
• Expanding offerings and extending market
reach

Types of UDDI nodes (1/3)
• Internal Enterprise Application UDDI node
– Web Services for use within a company for
internal enterprise application integration
– The scope can be single application,
departmental, corporate
– Sit behind the firewall
– Allow the service providers more control over
their service registry and its accessibility

• Portal UDDI node
– Web Services published by a company for external partners to find
and use
– Runs outside the service provider’s firewall
– Contains only those service descriptions that a company wishes to
provide to service requestors from external partners
• Partner catalog UDDI node
– Web services to be used by a particular company
– Runs behind the firewall
– Contains only approved, tested and valid Web service descriptions
for legitimate business partners

• E-Marketplace UDDI node
– Web Services that the service provider intends to
compete for requestors’ business with other Web
Services
– Hosted by an industry standards organization or
consortium
– Contains service descriptions from businesses in a
particular industry

Conclusion
• Web Serivices substitute for existing
distributed computing model such as RPC,
CORBA
• To apply to real e-business application, the
following problems should be covered
– Security
– Transaction Management
– QOS (ex., reliable message transmission)
– Efficient methods for composing Web Services

Web service architecture

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Web service architecture