introduction to ws

7/31/2019 Introduction to WS

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Introduction to Web Services

S.Sasirekha


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History Web services evolved from previous technologies

that served the same purpose such as RPC, ORPC(DCOM, CORBA and JAVA RMI).

Web Services were intended to solve three main

problems:1. Interoperability

2. Firewall traversal

3. Complexity


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Interoperability Earlier distributed systems suffered from

interoperability issues because each vendorimplemented its own on-wire format for distributedobject messaging.

Development of DCOM apps strictly bound to WindowsOperating system.

Development of RMI bound to Java programminglanguage.


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Firewall traversal Collaboration across corporations was an issue

because distributed systems such as CORBA andDCOM used non-standard ports.

Web Services use HTTP as a trans ort rotocol and

most of the firewalls allow access though port 80(HTTP), leading to easier and dynamic collaboration.


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Complexity Web Services is a developer-friendly service system.

Most of the above-mentioned technologies such asRMI, COM, and CORBA involve a whole learning curve.

New technologies and languages have to be learnt toimplement these services.


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Distributed Component

Technology


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Web Service definition

revisited A more precise definition:

an application component that: Communicates via open protocols (HTTP, SMTP,

etc.)

Describes its messages using XML Schema

Provides an endpoint description using WSDL

Can be discovered using UDDI


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Web Service Vs Web Application


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Web Services Components XML eXtensible Markup Language A uniform data

representation and exchange mechanism.

SOAP Simple Object Access Protocol A standardway for communication.

UDDI Universal Description, Discovery andIntegration specification A mechanism to registerand locate WS based application.

WSDL Web Services Description Language Astandard meta language to described the servicesoffered.


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Example A simple Web Service

A buyer (which might be a simple client) is ordering goods from aseller service.

The buyer finds the seller service by searching the UDDI directory.

The seller service is a Web Service whose interface is defined.

The buyer is invoking the order method on the seller service usingSimple Object Access Protocol (SOAP) and the WSDL definition forthe seller service.

The buyer knows what to expect in the SOAP reply messagebecause this is defined in the WSDL definition for the sellerservice.


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Web Services(In Practice)


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The Web Service Model The Web Services architecture is based upon the

interactions between three roles:

Service provider

Service registry

The interactions involve the:

Publish operations

Find operation

Bind operations.


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The Web Service Model (cont)The Web Services model follows the publish, find, and

bindparadigm.

1. publish 2. find

3. bind/invoke

Web ServiceRegistry

Web ServiceProvider

Web ServiceClient


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Web Service Protocol Stack


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XML XML stands for EXtensible Markup Language.

XML is a markup language much like HTML.

XML was designed to describe data.

XML tags are not predefined. You must define yourown tags.

The prefect choice for enabling cross-platform datacommunication in Web Services.


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XML vs HTMLAn HTML example:

John Doe

New York

045935435

[email protected]


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XML vs HTML This will be displayed as:

John Doe

2 Backroads Lane

HTML specifies how the document is to be displayed, and notwhat information is contained in the document.

Hard for machine to extract the embedded information.Relatively easy for human.

[email protected]


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XML vs HTML Now look at the following:

John Doe

2 Backroads Lane

In this case:

The information contained is being marked, but not fordisplaying.

Readable by both human and machines.

[email protected]


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SOAP SOAP originally stood for "Simple Object Access Protocol" .

Web Services expose useful functionality to Web usersthrough a standard Web protocol called SOAP.

Soap is an XML vocabulary standard to enable programs on.

a simple markup language for describing messagesbetween applications.

Soap uses mainly HTTP as a transport protocol. That is,HTTP message contains a SOAP message as its payload

section.


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SOAP Characteristics SOAP has three major characteristics:

Extensibility security and WS-routing are amongthe extensions under development.

Neutrality - SOAP can be used over any transportrotocol such as HTTP SMTP or even TCP.

Independent - SOAP allows for any programmingmodel .


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SOAP Building BlocksA SOAP message is an ordinary XML document

containing the following elements:

A required Envelope element that identifies theXML document as a SOAP message.

An o tional 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 themessage.


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SOAP RequestPOST /InStock HTTP/1.1

Host: www.stock.org

Content-Type: application/soap+xml; charset=utf-8 Content-Length: 150

IBM


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SOAP ResponseHTTP/1.1 200 OK

Content-Type: application/soap; charset=utf-8

Content-Length: 126

34.5


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SOAP Security SOAP uses HTTP as a transport protocol and hence

can use HTTP security mainly HTTP over SSL.

But, since SOAP can run over a number of applicationrotocols such as SMTP securit had to be

considered.

The WS-Security specification defines a completeencryption system.


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WSDL WSDL stands for Web Services Description Language.

WSDL is an XML vocabulary for describing Web services. It

allows developers to describe Web Services and theircapabilities, in a standard manner.

spec es w a a reques message mus con a n an

what the response message will look like in unambiguousnotation. In other words, it is a contract between the XMLWeb service and the client who wishes to use this service.

In addition to describing message contents, WSDL defineswhere the service is available and what communications

protocol is used to talk to the service.


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The WSDL Document Structure A WSDL document is just a simple XML document.

It defines a web service using these major elements: port type - The operations performed by the web

service. -

service. types - The data types used by the web service. binding - The communication protocols used by

the web service.


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WSDL Document


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UDDI UDDI stands for Universal Description, Discovery

and Integration.

UDDI is a directory for storing information aboutweb services like ellow a es.

UDDI is a directory of web service interfacesdescribed by WSDL.


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Yes

Yes


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