Introduction to WebServices

1. Introduction to
Web Services
Khasim

2. Web Services
• A Web service is a method of communication
between two electronic devices over
the World Wide Web
• In other words, a web service helps to convert
your application into a web-based application.

3. Why web services?
• Your application can publish its function or
message to the rest of the world.

4. Department of Information Science Engg
WEB
Services
REST Services SOAP and WSDL

5. REST Services
• Relying on URIs and HTTP verbs
• Usage of 5 big HTTP verbs
POST, HEAD, GET, PUT, DELETE
Nothing more than CRUD concept of the Web
• Ex: Delicious APIs
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• Data exchange format
XML, JASON or both

6. SOAP based services
• Simple Object Access Protocol
• Exclusively use XML as the data format to exchange info
over HTTP.
• A service that needs to be used by another service needs
to specify its usage through a “Service Description”.
• In this case, we use WSDL – Web Services Description
Language
• Ex: Apache Axis, Apache CXF
• SOAP has nothing to do with SOA – Service Oriented
Architecture

7. .

8. • A service is hosted on a “Discovery Service” in the internet.
• A client which wants to use this service will have to “discover”
this service (similar to RMI) using the ‘Discovery Service’.
• Once the service is “discovered”, the client asks the service
how it should be invoked. The service replies in WSDL format.
• The service is now invoked using SOAP. The client issues a
‘SOAP Request’.
• The service responds with a ‘SOAP Response’, which includes
the result.

9. A SOAP message is an ordinary XML document
containing the following elements:
• Envelope - identifies the XML document as a SOAP message
o Header - contains information about the request.
o Body
 Message data - contains request and response information
itself.
 Fault (optional) - containing errors and status information.

10. <?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.example.org/stock">
<m:GetStockPrice>
<m:StockName>IBM</m:StockName>
</m:GetStockPrice>
</soap:Body>
</soap:Envelope>
A SOAP request:

11. <?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.example.org/stock"
>
<m:GetStockPriceResponse>
<m:Price>34.5</m:Price>
</m:GetStockPriceResponse>
</soap:Body>
</soap:Envelope>
The SOAP response:

13. WSDL
• WSDL stands for Web Services Description Language
• It is an XML-based language that is used for
describing the functionality offered by a Web service.
• WSDL file contains info about
o How the service can be called
o What parameter it expects
o What data structure it returns
o Which port the application uses
o Which protocol the web service uses (like https)

14. Need for stubs (similar to RMI)

15. What are stubs?
• A stub is a small program routine that substitutes for
a longer program, possibly to be loaded later or that
is located remotely.
• The stub accepts the request and then forwards it
(through another program) to the remote procedure.
• When that procedure has completed its service, it
returns the results or other status to the stub which
passes it back to the program that made the request.

17. Comparision
REST services
• Architectural style
• Simply calls services via URL
path
• Lightweight – not a lot of
extra xml markup
• Easy to build – no toolkits
required
SOAP services
• XML-based protocol
• Invokes services by calling
RPC method
• Rigid – type checking,
adheres to a contract
• Development tools – WSDL
Soap analyser tool, oXygen
XML