Web Services Based on

SOA: Concepts, Technology, Designby Thomas Erl

MIS 181.9: Service Oriented Architecture

2nd Semester, 2011-2012

Web Services

►web-based applications that use open, XML-based standards and transport protocols to exchange data with clients

What are web services?

► Web services are application components► Web services communicate using open protocols► Web services are self-contained and self-

describing► Web services can be discovered using UDDI► Web services can be used by other applications► XML is the basis for Web services

How does it work?

►The basic Web services platform is XML + HTTP.► XML provides a language which can be used

between different platforms and programming languages and still express complex messages and functions.

► The HTTP protocol is the most used Internet protocol.

Web services model

Web Service Provider

Web Service Registry

Web Service Client

publish

bind/invoke

find

Web Services

►Technology Framework► Includes one or more of the following:

►Architectures►Technologies►Concepts►Models►Sub-frameworks

Web Services Framework

►Characterized by►Web services, service descriptions,

messages►Communications agreement (service

description) based on WSDL►Messaging framework using SOAP►Service description registration and

discovery architecture using UDDI

Web services platform elements

►SOAP (Simple Object Access Protocol)►UDDI (Universal Description, Discovery

and Integration)►WSDL (Web Services Description

Language)

Web services platform elements

UDDI

WSDL

SOAP

XML

Service Discovery and Publication

Service Description

XML based messaging

Data level description

Why use web services?

►Interoperability has Highest Priority►Web Services take Web-applications to

the Next Level►Web Services have Two Types of Uses

► Reusable application-components.► Connect existing software.

What is SOAP?

►stands for Simple Object Access Protocol ►an XML-based protocol to let applications

exchange information over HTTP►a protocol for accessing a Web Service

What is SOAP?

► a communication protocol► a format for sending messages► designed to communicate via Internet ► platform independent► language independent► based on XML► simple and extensible► SOAP allows you to get around firewalls► SOAP is a W3C standard

What is WSDL?

►an XML-based language for locating and describing Web services

► stands for Web Services Description Language► based on XML► used to describe Web services► used to locate Web services► a W3C standard

What is UDDI?

►a directory service where companies can register and search for Web services

► stands for Universal Description, Discovery and Integration

► a directory for storing information about web services► a directory of web service interfaces described by WSDL► communicates via SOAP► built into the Microsoft .NET platform

Web Services Design Concepts

►Web service can have two classifications►Temporary based on roles assumed

during runtime►Permanent based on application

logic it provides

Web Service Roles

►Web service can assume different roles depending on context of usage►Message Initiator►Message Relayer►Message Recipient

►Agnostic services

Service Roles► Service Provider

► Recipient of the request message

► Service Requestor► Any unit of processing logic capable of issuing a

request message► Searches for provider by reviewing Service

Descriptions

► Web Service is always a provider but can also be a requestor

Other roles

►Intermediaries►Service composition member

Intermediaries

► Web services communications is based on use of messaging paths► Vs. point-to-point communication► message sent by a requester can be processed

by multiple intermediate routing and processing agents before received by ultimate destination

► Intermediaries: web services that route and process a message► After initially sent► Before target destination

Service Composition Member

►Any service can enlist one or more additional services to complete a given task

►Any of the enlisted services can call other services to complete a given sub-task

Service Models

►Application logic classification►Business-related roles within a

solution

►Business service model►Utility service model►Controller service model

Business Service Model

►Most fundamental building block within SOA

►Encapsulates distinct set of business logic

Utility Service Model

►Any generic service designed for potential reuse

►Used in SOA as:► Services that are reused► Solution-agnostic intermediary services► Services with highest degree of

autonomy►Most commonly associated with the

application service layer

Controller Service Model

►Assembles and coordinates service compositions

►Used in SOA►To support and implement principle

of composability►To leverage reuse opportunities

►There can be master controller and sub-controller services

Service Descriptions

►WSDL used to define service descriptions

►Required to accompany any web service

►Service requestor uses WSDL of a service provider to ensure that messages sent is understood and accepted

Service endpoints

►WSDL describes the point of contact for a service provider

►Provides definition of endpoint interface►So requestor can know how to

structure request message►Establishes the physical location

(address) of the service

WSDL Definition

► Abstract Definition► Interface characteristics► Technology

Independent► portType/interface► operation

► Represents a specific action performed by a service

► Similar to public method

► message

WSDL Definition

►Concrete Description► Binding

►Technology transport►E.g. SOAP

► Port/endpoint►Physical address

SOAP

► Header► Meta information on how data

will be delivered and processed► Allows SOAP messages to be

independent► Sample instructions

► Processing► Routing/workflow► Security

► Body► XML formatted data

Service Description Advertisement and Discovery

►UDDI► One standard for structuring registries that

keep track of service descriptions► Registries can be searched manually or

automatically thru an API►Public Registries

► Accept registration from any organizations►Private Registries

► Can be implemented within an organization

UDDI Registry Records Components

►Business entities►For public registry records►Profile of business entity►Services offered by the entity

►Binding information►Can be an address of a web site►Can be a pointer to actual service

descriptions