1 / 29

Software Engineering COMP 201

This lecture focuses on distributed system architectures in software engineering, emphasizing architectural design for software that executes across multiple processors. It covers the characteristics of distributed systems, including resource sharing, scalability, and fault tolerance. Different models such as client-server and multiprocessor architectures are explored, alongside the role of middleware in managing distributed components. Key advantages and disadvantages of distributed systems will be analyzed to equip students with a comprehensive understanding of modern software engineering principles related to distributed computing.

rosie
Télécharger la présentation

Software Engineering COMP 201

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Software EngineeringCOMP 201 Lecturer: Sebastian Coope Ashton Building, Room G.18 E-mail: coopes@liverpool.ac.uk COMP 201 web-page: http://www.csc.liv.ac.uk/~coopes/comp201 Lecture 16 – Distributed System Architectures

  2. Distributed Systems Architectures Architectural design for software that executes on more than one processor COMP201 - Software Engineering

  3. Distributed Systems • Virtually all large computer-based systems are now distributed systems • Information processing is distributed over several computers rather than confined to a single machine • Distributed software engineeringis now very important COMP201 - Software Engineering

  4. System Types • Personal systemsthat are not distributed and that are designed to run on a personal computer or workstation. • Embedded systemsthat run on a single processor or on an integrated group of processors. • Distributed systemswhere the system software runs on a loosely integrated group of cooperating processors linked by a network. COMP201 - Software Engineering

  5. Distributed System Characteristics • Resource sharing • Openness • Concurrency • Scalability • Fault tolerance • Transparency Distributed system disadvantages : Complexity Security Manageability Unpredictability COMP201 - Software Engineering

  6. Distributed Systems Architectures • Client-server architectures • Distributed services which are called on by clients. Servers that provide services are treated differently from clients that use services • Distributed object architectures • No distinction between clients and servers. Any object on the system may provide and use services from other objects COMP201 - Software Engineering

  7. Middleware • Software that manages and supports the different components of a distributed system. In essence, it sits in the middleof the system • Middleware is usually off-the-shelf rather than specially written software • Examples • Transaction processing monitors • Data converters • Communication controllers COMP201 - Software Engineering

  8. 1. Multiprocessor Architectures • Simplest distributed system model • Systemcomposed of multiple processes which may (but need not) execute on different processors • Architectural model of many large real-time systems • Distribution of process to processor may be pre-ordered or may be under the control of a dispatcher COMP201 - Software Engineering

  9. A Multiprocessor Traffic Control System COMP201 - Software Engineering

  10. 2. Client-Server Architectures • The application is modelled as a set of servicesthat are provided by servers and a set of clients that use these services • Clients know of servers but servers need not know of clients • Clients and servers are logical processes • The mapping of processors to processes is not necessarily 1 : 1 COMP201 - Software Engineering

  11. A Client-Server System COMP201 - Software Engineering

  12. Computers in a C/S Network COMP201 - Software Engineering

  13. Layered Application Architecture • Presentation layer • Concerned with presenting the results of a computation to system users and with collecting user inputs • Application processing layer • Concerned with providing application specific functionality e.g., in a banking system, banking functions such as open account, close account, etc. • Data management layer • Concerned with managing the system databases COMP201 - Software Engineering

  14. Application Layers COMP201 - Software Engineering

  15. Thin and Fat Clients • Thin-client model • In a thin-client model, all of the application processing and data management is carried out on the server. The client is simply responsible for running the presentation software. • Fat-client model • In this model, the server is only responsible for data management. Thesoftware on the client implements the application logic and the interactions with the system user. COMP201 - Software Engineering

  16. Thin and Fat Clients COMP201 - Software Engineering

  17. Thin Client Model • Used when legacy systems are migrated to client server architectures. • The legacy system acts as a server in its own right with a graphical interface implemented on a client • A major disadvantage is that it places a heavy processing load on both the server and the network COMP201 - Software Engineering

  18. Fat Client Model • More processing is delegated to the client as the application processing is locally executed • Most suitable for new client-server systems where the capabilities of the client system are known in advance • More complex than a thin client model especially for management. New versions of the application have to be installed on all clients COMP201 - Software Engineering

  19. A Client-Server ATM System COMP201 - Software Engineering

  20. Three-Tier Architectures • In a three-tier architecture, each of the application architecture layers may execute on a separate processor • Allows for better performance than a thin-client approach and is simpler to manage than a fat-client approach • A more scalable architecture - as demands increase, extra servers can be added to the data management or application processing layers. COMP201 - Software Engineering

  21. A 3-Tier Client-Server Architecture COMP201 - Software Engineering

  22. An Internet Banking System COMP201 - Software Engineering

  23. Use of Client-Server Architectures COMP201 - Software Engineering

  24. 3. Distributed Object Architectures • There is no distinction in a distributed object architectures between clients and servers • Each distributable entity is an object that • provides services to other objects and • receives services from other objects • Object communication is through a middleware system called an object request broker (software bus) • However, they can be more complex to design than client-server systems COMP201 - Software Engineering

  25. Distributed Object Architecture COMP201 - Software Engineering

  26. Advantages of Distributed Object Architecture • It allows the system designer to delay decisions on where and how services should be provided • Service-providing objects can execute on any node of the network and thus the distinction between thin/fat-client models becomes irrelevant. • It is a very open system architecture that allows new resources to be added to it as required • Object communication standards have been developed allowing objects written in different languages to communicate with each other. COMP201 - Software Engineering

  27. Advantages of Distributed Object Architecture • The system is flexible and scalable • New objects can be added as the load on the system increases without disrupting the other system objects. Replicated object can be created to cope with load. • It is possible to reconfigure the system dynamically with objects migrating across the network as required • This may be important when there is fluctuating patterns of demand on services. A service-providing object can migrate to the same processor as service-requesting objects, thus improving performance. COMP201 - Software Engineering

  28. Lecture Key Points • Client-server systems are distributed systems where the system is modelled as a set of services provided by servers to client processes. • In a client-server system, the user interface always runs on a client and data management is always provided by a shared server. • Application functionality may be implemented on the client computer or the server. COMP201 - Software Engineering

  29. Lecture Key Points • In a distributed object architecture, there is no distinction between clients and servers; objects provide general services that may be called on by other objects. • Distributed object systems require middleware to handle object communications and to allow objects to be added or removed from the system. COMP201 - Software Engineering

More Related