Web Services

                                     Web Service Introduction

Web service is the strongest era of 20th  century to develop multi language  multi platform enterprise application.Nowadays every IT industry is bound to use web services to enhance their business in a sophisticated manner so that they can enhance their business with so many partner.

Web services is not a technology which has been launched by a vender rather it is a group of multiple standard and specification provided by  multiple vendor to developed a web based distributed application which can run in architectural neutral and language independent manner.


Service Oriented Architecture

Service-oriented architecture (SOA) is an evolution of distributed computing based on the request/reply design paradigm for synchronous and asynchronous applications. An application's business logic or individual functions are modularized and presented as services for consumer/client applications. The key to these services is their loosely coupled nature; i.e., the service interface is independent of the implementation. Application developers or system integrators can build applications by composing one or more services without knowing the services' underlying implementations.
 For example, a service can be implemented either in .Net or J2EE, and the application consuming the service can be on a different platform or language.


Web services is  based on Service Oriented Architecture(SOA) which is a plan rather than implementation to develop a web based distributed application..

Annotated Web services architecture graphic

Every SOA based  application will have following characteristics....

  • SOA services have self-describing interfaces in platform-independent XML documents. Web Services Description Language (WSDL) is the standard used to describe the services. 
  • SOA services communicate with messages formally defined via XML Schema (also called XSD). Communication among consumers and providers or services typically happens in heterogeneous environments, with little or no knowledge about the provider. Messages between services can be viewed as key business documents processed in an enterprise.
  • SOA services are maintained in the enterprise by a registry that acts as a directory listing. Applications can look up the services in the registry and invoke the service. Universal Description, Definition, and Integration (UDDI) is the standard used for service registry.
  • Each SOA service has a quality of service (QoS) associated with it. Some of the key QoS elements are security requirements, such as authentication and authorization, reliable messaging, and policies regarding who can invoke services
A web service consist of combination of webservice standard and specification.
There are so many usable specification  are available in market  which  are combining to develop web service based application..

  Specification of Web Services..                                                   

XML Specification                                                  

    XML (extensible Markup Language)
    XML Namespaces
    XML Schema
    XPath
    XQuery
    XML Information Set
    XInclude
    XML Pointer

Messaging Specification

    SOAP (formerly known as Simple Object Access Protocol)
    SOAP-over-UDP[3]
    SOAP Message Transmission Optimization Mechanism
    WS-Notification
        WS-BaseNotification
        WS-Topics
        WS-BrokeredNotification
    WS-Addressing
    WS-Transfer
    WS-Eventing
    WS-Enumeration
    WS-MakeConnection
 

Metadata Exchange Specification

    JSON-WSP
    WS-Policy
    WS-PolicyAssertions
    WE-PolicyAttachment
    WS-Discovery
        WS-Inspection
    WS-MetadataExchange
    Universal Description Discovery and Integration (UDDI)
    WSDL 2.0 Core
    WSDL 2.0 SOAP Binding
        Web Services Semantics (WSDL-S)
    WS-Resource Framework (WSRF)
 

Security Specification

    WS-Security
    XML Signature
    XML Encryption
    XML Key Management (XKMS)
    WS-SecureConversation
    WS-SecurityPolicy
    WS-Trust
    WS-Federation
    WS-Federation Active Requestor Profile
    WS-Federation Passive Requestor Profile
    Web Services Security Kerberos Binding
    Web Single Sign-On Interoperability Profile
    Web Single Sign-On Metadata Exchange Protocol
    Security Assertion Markup Language (SAML)
    XACML
 

 The web service standard are  mentioned below.

  •     IBM developerWork: Standard and Web Service
  •     innoQ's WS-Standard
  •     MSDN .NET Developer Centre: Web Service Specification Index Page
  •     OASIS Standards and Other Approved Work
  •     Open Grid Forum Final Document
  •     XML CoverPage
  •     W3C's Web Services Activity

In industry developer works to develop service based application using above specification.
The most commonly usable standard are..

  • Wsdl(Web service description language)
  • Soap(Simple object access protocol)
  • Ws-Security(Web service Security)
A simple web service application will be devloped by using the  the above specification and we have to implement ..
Web service description language
It is a language  which is platform independent ,architecture neutral which is the heart to develop a web service application.
  •     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 a W3C recommendation
WSDL is a document written in XML. The document describes a Web service. It specifies the location of the service and the operations (or methods) the service exposes.  

A WSDL file contains following element to specify the service in xml language.

element Name
                                          Description
types
A container for abstract type definitions defined using XML Schema
message
A definition of an abstract message that may consist of multiple parts, each part may be of a different type
port Type
An abstract set of operations supported by one or more endpoints (commonly known as an interface); operations are defined by an exchange of messages
binding
A concrete protocol and data format specification for a particular portType
service
A collection of related endpoints, where an endpoint is defined as a combination of a binding and an address (URI)
 

A simple wsdl file is mentioned below...
<definitions xmlns="http://schemas.xmlsoap.org/wsdl/" 
  xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" 
  xmlns:http="http://schemas.xmlsoap.org/wsdl/http/" 
  xmlns:xs="http://www.w3.org/2001/XMLSchema" 
  xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/" 
  xmlns:mime="http://schemas.xmlsoap.org/wsdl/mime/" 
  xmlns:y="http://example.org/math/" 
  xmlns:ns="http://example.org/math/types/" 
  targetNamespace="http://example.org/math/">
   <types>
     <xs:schema targetNamespace="http://example.org/math/types/" 
       xmlns="http://example.org/math/types/" 
       elementFormDefault="unqualified" attributeFormDefault="unqualified">
         <xs:complexType name="MathInput">
            <xs:sequence>
               <xs:element name="x" type="xs:double"/>
               <xs:element name="y" type="xs:double"/>
            </xs:sequence>
         </xs:complexType>
         <xs:complexType name="MathOutput">
            <xs:sequence>
               <xs:element name="result" type="xs:double"/>
            </xs:sequence>
         </xs:complexType>
         <xs:element name="Add" type="MathInput"/>
         <xs:element name="AddResponse" type="MathOutput"/>
         <xs:element name="Subtract" type="MathInput"/>
         <xs:element name="SubtractResponse" type="MathOutput"/>
         <xs:element name="Multiply" type="MathInput"/>
         <xs:element name="MultiplyResponse" type="MathOutput"/>
         <xs:element name="Divide" type="MathInput"/>
         <xs:element name="DivideResponse" type="MathOutput"/>
      </xs:schema>
   </types>
   <message name="AddMessage">
      <part name="parameters" element="ns:Add"/>
   </message>
   <message name="AddResponseMessage">
      <part name="parameters" element="ns:AddResponse"/>
   </message>
   <message name="SubtractMessage">
      <part name="parameters" element="ns:Subtract"/>
   </message>
   <message name="SubtractResponseMessage">
      <part name="parameters" element="ns:SubtractResponse"/>
   </message>
   <message name="MultiplyMessage">
      <part name="parameters" element="ns:Multiply"/>
   </message>
   <message name="MultiplyResponseMessage">
      <part name="parameters" element="ns:MultiplyResponse"/>
   </message>
   <message name="DivideMessage">
      <part name="parameters" element="ns:Divide"/>
   </message>
   <message name="DivideResponseMessage">
      <part name="parameters" element="ns:DivideResponse"/>
   </message>
   <portType name="MathInterface">
      <operation name="Add">
         <input message="y:AddMessage"/>
         <output message="y:AddResponseMessage"/>
      </operation>
      <operation name="Subtract">
         <input message="y:SubtractMessage"/>
         <output message="y:SubtractResponseMessage"/>
      </operation>
      <operation name="Multiply">
         <input message="y:MultiplyMessage"/>
         <output message="y:MultiplyResponseMessage"/>
      </operation>
      <operation name="Divide">
         <input message="y:DivideMessage"/>
         <output message="y:DivideResponseMessage"/>
      </operation>
   </portType>
   <binding name="MathSoapHttpBinding" type="y:MathInterface">
      <soap:binding style="document" 
         transport="http://schemas.xmlsoap.org/soap/http"/>
      <operation name="Add">
         <soap:operation soapAction="http://example.org/math/#Add"/>
         <input>
            <soap:body use="literal"/>
         </input>
         <output>
            <soap:body use="literal"/>
         </output>
      </operation>
      <operation name="Subtract">
         <soap:operation soapAction="http://example.org/math/#Subtract"/>
         <input>
            <soap:body use="literal"/>
         </input>
         <output>
            <soap:body use="literal"/>
         </output>
      </operation>
      <operation name="Multiply">
         <soap:operation soapAction="http://example.org/math/#Multiply"/>
         <input>
            <soap:body use="literal"/>
         </input>
         <output>
            <soap:body use="literal"/>
         </output>
      </operation>
      <operation name="Divide">
         <soap:operation soapAction="http://example.org/math/#Divide"/>
         <input>
            <soap:body use="literal"/>
         </input>
         <output>
            <soap:body use="literal"/>
         </output>
      </operation>
   </binding>
   <service name="MathService">
      <port name="MathEndpoint" binding="y:MathSoapHttpBinding">
         <soap:address location="http://localhost/math/math.asmx"/>
      </port>
   </service>
</definitions>
 
A wsdl is a mediator to talk with  different technology and language.In otherwords it provides
abstraction on technology  dependant language and uses a common language  called xml to expose
the service to the service client. 
 
 
 
 

Simple Object Access Protocol

Soap is protocol which runs over Http protocol and is called "soap over http" interms of webservice.
It is a application level protocol which depends upon HTTP  to send the data over the data. It uses xml language to transfer the data over the network.
 In simply a soap protocol...
  • SOAP stands for Simple Object Access Protocol
  • SOAP is a communication protocol
  • SOAP is for communication between applications
  • SOAP is a format for sending messages
  • SOAP communicates via Internet
  • SOAP is platform independent
  • SOAP is language independent
  • SOAP is based on XML
  • SOAP is simple and extensible
  • SOAP allows you to get around firewalls
A simple soap message is looks like

<?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:Header>
...
</soap:Header>

<soap:Body>
...
  <soap:Fault>
  ...
  </soap:Fault>
</soap:Body>

</soap:Envelope> 
A simple soap message contains  two parts.
  • Soap Header
  • Soap Body
  • Soap Fault
The combination of soap header ,soap body and soap fault is called soap envelope.

 Soap Header

SOAP Header element can be explained as:
  • Header elements are optional part of SOAP messages.
  • Header elements can occur multiple times.
  • Headers are intended to add new features and functionality
  • The SOAP header contains header entries defined in a namespace.
  • The header is encoded as the first immediate child element of the SOAP envelope.
  • When more than one header is defined, all immediate child elements of the SOAP header are interpreted as SOAP header blocks.

    The most important part of soap header is ,it contains security information. 

    SOAP Header  is optional and the element contains application-specific information (like authentication, payment, etc) about the SOAP message.
    If the Header element is present, it must be the first child element of the Envelope element.
SOAP Header element can have following two attributes
  • Actor attribute:
    The SOAP protocol defines a message path as a list of SOAP service nodes. Each of these intermediate nodes can perform some processing and then forward the message to the next node in the chain. By setting the Actor attribute, the client can specify the recipient of the SOAP header.
  • MustUnderstand attribute
    Indicates whether a Header element is optional or mandatory. If set to true ie. 1 the recipient must understand and process the Header attribute according to its defined semantics, or return a fault.
    A typical soap header structure is like...

    <?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:Header>
      <m:Trans xmlns:m="http://www.w3schools.com/transaction/"
      soap:mustUnderstand="1">234
      </m:Trans>
    </soap:Header>
    ...
    ...
    </soap:Envelope>

Soap Body

SOAP Body   is the required element contains the actual SOAP message intended for the ultimate endpoint of the message.
A soap body contains the actual data which is supposed to be send across the network through the http request 
soap body is the  immediate child elements of the SOAP Body element may be namespace-qualified.
A typical soap body message contains two parts.
  • Soap Request
  • Soap Response
Soap Request contains the actual data which is intended to be send to get the response.
Soap Response contain the response data which contains the information.In otherwords it is called processed data
 .
A typical soap body with request data is  looks  like  below....
<?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>
  <m:GetPrice xmlns:m="http://www.w3schools.com/prices">
    <m:Item>Apples</m:Item>
  </m:GetPrice>
</soap:Body>

</soap:Envelope> 

And the response body contains..
<?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>
  <m:GetPriceResponse xmlns:m="http://www.w3schools.com/prices">
    <m:Price>1.90</m:Price>
  </m:GetPriceResponse>
</soap:Body>

</soap:Envelope> 
 Here Apple is the item which has to send to the webservice to get the price and is called request made by webservice client and 1.90 is the response to the webservice client on behalf of the request.




 

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