Description of soa and SOAP,WSDL & UDDI

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Tushar Varshney

Description of SOA and SOAP,WSDL&UDDI

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Service-oriented architectures

A means of developing distributed systems where the components are stand-alone services.

Services may execute on different computers from different service providers.

Standard protocols have been developed to support service communication and information exchange.

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Services or components?

A service can be defined as: A loosely-coupled, reusable software component that

encapsulates discrete functionality which may be distributed and programmatically accessed. A web service is a service that is accessed using standard Internet and XML-based protocols.

A critical distinction between a service and a component as defined in component-based software engineering is that services are independent. Services do not have a ‘requires’ interface. Services rely on message-based communication with

messages expressed in XML.

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Benefits of SOA

Services can be provided locally or outsourced to external providers.

Services are language-independent. Investment in legacy systems can be

preserved. Inter-organizational computing is facilitated

through simplified information exchange.

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SOA and Web Services

Service-oriented architecture is an architectural style Derived from the client-server architectural style. Clients (service consumers or requesters) and servers

(service providers) connected by a service “bus”. Services defined using formal interfaces (contracts). Service bus supports point-to-point and messaging styles

of communication. Support for system qualities, e.g., security and transaction

management.

Web services Services provided in a SOA deployed over the web.

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Key standards

SOAP (Simple Object Access Protocol) A message exchange standard that supports service

communication.

WSDL (Web Service Definition Language) This standard allows a service interface and its bindings to

be defined.

UDDI (Universal Description Discovery and Integration) Defines the components of a service specification that may

be used to discover the existence of a service.

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Service-oriented architectureUDDI

SOAP

WSDL

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SOAP messages

SOAP is based on message exchanges

Messages are seen as envelops where the application encloses the data to be sent

A message has two main parts: header: which can be divided into

blocks body: which can be divided into

blocks SOAP does not say what to do with

the header and the body, it only states that the header is optional and the body is mandatory

Use of header and body, however, is implicit. The body is for application level data. The header is for infrastructure level data

SOAP Envelope

SOAP header

Header Block

SOAP Body

Body Block

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SOAP EnvelopeSOAP EnvelopeSOAP header

Transactionalcontext

SOAP Body

Input parameter 1

Input parameter 2

Name of Procedure

HTTP POST

SOAP EnvelopeSOAP EnvelopeSOAP header

Transactionalcontext

SOAP Body

Return parameter

HTTP Acknowledgement

SERVICE REQUESTER SERVICE PROVIDER

RPC call

HTTP

engine

SOAPengine

Procedure

HTTP

engine

SOAPengine

SOAP and HTTP

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Web service description language

The service interface is defined in a service description expressed in WSDL. The WSDL specification defines: What operations the service supports and the format of the

messages that are sent and received by the service. How the service is accessed - that is, the binding maps the

abstract interface onto a concrete set of protocols. Where the service is located. This is usually expressed as

a URI (Universal Resource Identifier).

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Structure of a WSDL specification

Intro

Abstract interface

Concreteimplementation

WSDL service definition

XML namespace declarations

Type declarationsInterface declarations

Message declarations

Binding declarationsEndpoint declarations

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A UDDI description

Details of the business providing the service. An informal description of the functionality

provided by the service. Information where to find the service’s WSDL

specification. Subscription information that allows users to

register for service updates.

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Standards for web service composition

Service orchestration WS-BPEL is an XML-based language for workflow

specification. WS-BPEL is an “orchestration” language.

Service orchestration defines the sequence and conditions in which one Web service invokes other Web services.

Can be used to create a composite service out of other services.

Service choreography WS-CDL is an XML-based language for describing service

“choreography”. Choreography defines the allowable message

exchanges between services.

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Orchestration vs. choreography

Orchestration A Single Director In Control.

Choreography Defines Interaction.

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Orchestration and choreography example

Requestprocessor

Setup jobparameters

Downloaddata

Startcomputation

Storeresults

Reportcompletion

Restart

Fail

CheckAvailability

Allocateresources

Initialise Compute

Returnresults

OK

No processor

OK

Orchestration within services

Choreography between services

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Choreography perspective

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Orchestration perspective

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Orchestration and choreography