1. DISTRIBUTED WEB-BASED SYSTEMS

2. Contents
•Architecture
•Multitier Architecture
•Web Service
•References

3. Architecture
Web-based distributed systems
•Fundamentally same as other distributed systems
•Dynamical documents with active elements
•Introduction of services

4. Architecture
Traditional Web-Based Systems
•Relatively simple client-server architecture
•Access to local file system
•Simplest way to refer a document is by Uniform Resource Locator (URL)
•URL specifies the application-level protocol for transfers across the network
•Several different protocols

5. Architecture
Traditional Web-Based Systems
•Browser and its responsibilities
•Communication between browser and web server
•HTTP

6. Architecture
Traditional Web-Based Systems - Organization

7. Architecture
Web Documents
•All information comes in the form of a document
•Documents may include all kinds of dynamic features
•Documents can be divided into two parts:
• Main part which acts as a template for second part
• Second part which contains different bits and pieces
•Main part is written in markup language, most widely used markup language is HTML

8. Architecture
Web Documents
•XML is another important markup language
•XML is more flexible and includes definitions of the elements
•Embedded documents and handling them
•Multipurpose Internet Mail Exchange (MIME)
•Special application type documents

9. Architecture
Web Documents

10. Multi Tier Architecture
Static Web Pages
•Locates and returns the object identified in the request.
•Includes predefined HTML pages and JPEG ad GIF files.
•Web servers do not require communication with any server side application

11. Multi Tier Architecture
Dynamic Web Pages
•The request is forwarded to an application system where the response is generated dynamically
on the server by server side program execution.
•The combination of HTML or XML with scripting provides powerful means of expressing
documents.

12. Multi Tier Architecture
Common Gateway Interface
•Enhancements are made to the two tier client-server system to support advanced type of
documents.
•Common Gateway Interface is standard way by which a Web server can execute a program
taking the user input.

13. Multi Tier Architecture
Server side CGI programs

14. Multi Tier Architecture
•Because of server-side processing many websites are now organized as three-tiered
architectures consisting of web server, application server and database server.
•Server-side scripting technologies used to generate dynamic content
• Active Server Pages
• Java Server Pages
• Java Script

15. Multi Tier Architecture

16. Web Service
•client-side software of a Web-based system consists of a browser that acts as the interface to a
user
•Web-based systems that are offering general services to remote applications without immediate
interactions from end users

17. Web Service
Web Services Fundamentals
• Web service is nothing but a traditional service that is made available over the Internet (such
as naming service, weather reporting service)
• Web service is adhere to collection of standards that will allow it to be discovered and
accessed over the Internet by client applications that follow those standards as well

18. Web Service
Web Services Fundamentals
• Principle of providing and using a Web service(similar to remote procedure call)

19. Web Service
Web Services Fundamentals --- Web service information storing
• directory service storing service descriptions, it is adhere to Universal Description, Discovery
and Integration standard (UDDI)
• UDDI prescribes the layout of a database containing service descriptions that will allow Web
service clients to browse for relevant services.

20. Web Service
Web Services Fundamentals --- Description language
• Services are described by means of the Web Services Definition Language (WSDL)
• A WSDL description contains the precise definitions of the interfaces provided by a service,
that is, procedure specification, data types, the (logical) location of services
• An important issue of a WSDL description is that can be automatically translated to client
+side and server-side stubs

21. Web Service
Web Services Fundamentals --- Communication
• the Simple Object Access Protocol (SOAP) is used to determine how communication take
place
• SOAP is essentially a framework in which much of the communication between two processes
can be standardized

22. Web Service
Web Services --- Composition and Coordination
So far, Web service is offered in the form of a single invocation.
Complexity increases when considering Web services that are offered by combining Web
services from different providers, we need to coordinate these services
In practice, it is more
complex

23. Web Service
Web Services --- Composition and Coordination
• First, how can the coordination between Web services, possibly from different organizations,
take place?
• Second, how can services be easily composed?

24. Web Service
Web Services --- Composition and Coordination
• First, how can the coordination between Web services, possibly from different organizations,
take place?
• Second, how can services be easily composed?

25. Web Service
Web Services Composition and Coordination --- Coordination
protocols
• Coordination protocols prescribes the various steps that need to take place for (composite)
service to succeed.( simplest way is to have single coordinator that controls the messages
exchanged between the participating parties)
a. When a party wants to participate in a specific protocol, that it knows with which other
process(es) it should communicate
b. process is involved in multiple coordination protocols at the same time. Therefore, identifying the
instance of a protocol is important as well
c. A process should know which role it is to fulfill.

26. Web Service
Web Services Composition and Coordination --- Web Services
Coordination
• These issues are standardized in what is known as web Services Coordination( Frend et.al
2005), it defines a separate service for handling coordination. The whole idea is that such a
service would implement the coordinator for various protocol instances

27. Web Service
Web Services Composition and Coordination--- web Services
Coordination
• A process can request the activation of a specific protocol
• Once all participants have registered, the coordinator can send the VOTE_REQUEST, COMMIT,
and other messages

28. References
1) Andrew S. Tanenbaum, Maarten Van Steen, “Distributed Systems: Principles and Paradigms”,
Prentice-Hall,NJ,USA.
2) Alonso, G., Myths around Web Services. IEEE Data Engineering Bulletin, Volume 25, number 4,
2002.
3) Engelen, R. van, Code Generation Techniques for Developing Light-weight XML Web Services for
Embedded Devices, ACM SAC’04,
4) Fowler, M., Patterns of Enterprise Application Architecture. Addison-Wesley Professional,
5) Jammes, F., H. Smit. Service-Oriented Paradigms in Industrial Automation, Industrial Informatics
6) A framework of a Web-based distributed control system, Electrical and Computer Engineering,
2003, 1351 - 1354 vol.2
7) http://ecet.ecs.uni-ruse.bg/cst06/Docs/cp/SIII/IIIA.24.pdf

29. Thank you