Inter-Communication of Software Applications
There are different techniques used for the communication
between software applications. These techniques vary from platforms to the
technologies used for implementation of software applications, like
–
RMI is used for inter-communication for java
based software applications
–
CORBA
–
RPC etc.
•
The above techniques and protocols have
technology and architectural dependencies for inter-application communication
over.
•
To overcome the technical, cross platform and
architectural issues the concept of WebService is
introduced.
Utility Computing
Web Service is based on Utility Computing model
Web Service Conceptual Definitions
Definition: Web Service is a technique (Architectural
design and specification) which enables electronic devices (Computing Devices)
communication over World Wide Web. http://en.wikipedia.org/wiki/Web_service
According to the Utility computing (Cloud computing)
Definition: A software application or component
available on web as a service.
According to the W3 Architecture
Definition: A software application identified by URI,
whose public interfaces and bindings are defined and described using XML.
–
This application can be discovered by other
software applications.
–
The other software applications can communicate
with application (Web Service) according to its defined rules by XML messages
over internet protocols.
–
According to the W3C
http://www.w3.org/TR/2002/WD-ws-arch-20021114/#whatisws
Definition: A software application designed for
inter-devices communication over internet.
–
Web Service has standard interface for
communication defined according to the WSDL
–
Web Service enables communication through SOAP
messages over http with XML serialization
Web Service Architecture
Definition: Web Service Architecture has three main
components. One of them has further two parts.
- Service(Software
Application)
- Service
Agency (UDDI)
- Service
Provider
- Service Requester
According to the W3 team Architecture of Web Service has no
strict components involved for the success of functionality, but all the
members (Architects, Analysts and Developers) were agreed that the Web Service
architecture should have following capabilities
–
Web Service architecture should be able to
exchange messages
–
Web Service architecture should be able to define its description
–
Web Service architecture should be able to publish and discover the
web service descriptions
Client Server Paradigm
•
Web Service follows the client server
architecture. Where service requester acts as client (Web browser or any
software application) and the Service provider acts as server.
•
For communication any internet protocol can be
used like HTTP or SMTP etc but HHTP has become standard
1. Service (Software Application)
- Service is a software
application implemented according to the description of WSDL.
- Service can be invoked by
other software application any time from any where on internet.
- Service can be
implemented using any technology like JAVA, Python etc.
- Service can be deployed
on any platform
- Service also can act as
service requester by using other web services.
- Service is accessed by
HTTP protocol.
- Service can also be
accessed by other internet protocols like SMTP but HTTP is used in most
of the cases.
- Messages are composed and exchanged in XML format
2. Service Discovery Agency (UDDI)
1.
Service discovery agency is a searchable set of
instructions and descriptions those can be searched by any software application
on internet
2.
It contains service descriptions and
implementation details
3.
It contains the metadata about service like
4.
Data types
5.
MIME types
6.
Operations
7.
Binding Information
8.
Network address
9.
It may be centralized or distributed
10.
It works for both providers and requestors
11.
Requestors can use discovery agency to find the
descriptions and address of the services
12.
Providers can use the discovery agency to
publish the address and descriptions of the services
13.
Requestor/Provider can also be used as UDDI
3. Service Requestor (Client)
Business definition: A
business that requires certain function to be satisfied
Technical Definition: Service
Requestor is software application which requests the required
function (service) from service
provider
- Service Requestor may be
a whole application or a component of the application
- Requestor may be a http
browser or any software application
How Service Requestor works
•
The requestor first of all find the description,
location and binding details from discovery registry and then interact with
service provider.
•
Here are two main operations those are done by
Service Requestor
1. Find:
–
In the find operation, the service requestor
retrieves a service description directly from provider or queries the discovery
registry for the type of service required.
–
The find operation can be done on two phases
–
To retrieve the service's interface description
for program development at design phase
–
To retrieve the service's binding and location
description for invocation at run time.
2. Interact:
–
After getting the address, description and
binding details of services the requestor invokes the service through binding
details
4. Service Provider (Software Application)
According to the architect group
who defined the web services ‘Service Provider’ is a server who provides the
environment to execute the service ‘Web service application’.
Service provider provides the
whole mechanism to run the web service application and to access it from remote
side on www.
How Service Provider publish services
•
For any web service is necessary that it is
accessible over the internet.
•
No service can be accessed while it is not
discovered.
•
For service discovery, it is necessary that is
published first.
•
Service provider publish the following details
(Metadata) about the hosted service for discovery
–
Description about service
–
Data types
–
Used functions
–
Proposed functions
–
Location
–
Provide/Consumer MIME types
–
Bindings
•
The above explained details are published in WSDL
(XML) document
•
The service requester can find the WSDL (XML)
document from discovery registry and can communicate with provider
How Web Service Works?
• First
of all Service Requestor (Web browser, Software application) finds the metadata
(Description, location, binding, functions) from discovery registry in WSDL
(XML) document form.
• Note:
Requestor can also find these information directly from its own directory like
if the same service is requested earlier
• After
finding the WSDL document the requestor composes the SOAP message in XML format
and sends it to the service provider through http protocol
• After
receiving http request the server composes the response message (SOAP message)
according the WSDL specifications and send it to the requested client.
• The
server sends back the response message if requester has requested the response
else server does not send response
