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CSIS0402 System Architecture

CSIS0402 System Architecture. K.P. Chow University of Hong Kong. Vendor Architectures. Purpose: Products positioning: help to look at the forest not the trees Skeleton for clients: tell clients how to develop using their products Marketing: help market their products

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CSIS0402 System Architecture

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  1. CSIS0402 System Architecture K.P. Chow University of Hong Kong

  2. Vendor Architectures • Purpose: • Products positioning: help to look at the forest not the trees • Skeleton for clients: tell clients how to develop using their products • Marketing: help market their products • Historical vendor architectures: IBM SAA, OSF DCE, OMG OMA, MS DNA • Vendors middleware architectures: the 2 most popular ones: • Microsoft .NET Distributed Architecture • SunSoft J2EE: Java 2 Enterprise Edition

  3. Java GUI application Web browser + Applets J2EE RMI-IIOP HTML DHTML XML JDBC JMS JNDI Presentation Tier Java Servlet JSP Web Container RMI-IIOP Java mail JDBC JMS JNDI EJB container EJB Business Logic Tier conn-ector RMI-IIOP Java mail JDBC JMS JNDI Data Tier Data Mainframe

  4. J2EE Components • The client tier: either browser, with Java Applets, or an Java program • The Web tier: a Web server running Java Server Page (JSP) and Java Servlet • The Enterprise Java Beans Tier: an EJB container • The Enterprise Information System tier: a database or a mainframe application • The common building blocks are Java components

  5. VB C# C++ J# … .NET Framework Common Language Specification ASP.NET (Web Forms, Web Services, Mobile Internet Toolkit) Windows Forms ADO.NET and XML Base Class Library Common Language Runtime Operating System

  6. Rich Client (GUI appn) Thin Client (Web browser) .NET Distributed Architecture HTML DHTML XML ADO & OLE DB DCOM MSMQ Presentation Tier ASP IIS Web Server DCOM ADO & OLE DB MSMQ .NET component COM+ container Business Logic Tier COMTI DCOM ADO & OLE DB MSMQ Data Tier E-mail & Messaging Directory SQL Database File System Mainframe

  7. .NET Distributed Architecture Components • Presentation services: includes HTML, DHTML, scripting, ActiveX, .NET components • Application services: includes Internet Information Server (IIS), COM+, MSMQ • Data services: Universal data access includes ADO and OLE DB • System services: includes directory, security, management and network • Common building blocks are .NET components

  8. Distributed Architecture • Distributed processing technology • Transaction technology • Information retrieval technology, e.g. MIS reports • Collaborative technology, e.g. e-mail • Internal distributed services, e.g. software distribution, remote systems operation • Distributed architecture patterns: • Middleware bus architecture • Hub architecture • Loosely coupled architecture

  9. Middleware Bus Architecture (1) Web Server Voice Server Workstation Server B2B Server Middleware Order Entry Delivery Warehouse Billing Accounts Marketing

  10. Middleware Bus Architecture (2) • Used in early days distributed systems implementation: middleware software is implemented by the organization • Aim to separate the presentation channels from the business services: middleware provides access to the core services • Either using real-time messages or deferred messages • Advantages: • Fast: hardware and software are tailored for the production workload • Secure: installed within an enterprise, usually well protected • Flexible: new channel can be added easily • Support customized requirements, e.g. resiliency • Problem: maintenance of the middleware • Tightly coupled architecture: both the sender and receiver must use the same technology, follow the same protocol, and understand a common format for the messages

  11. Hub Architecture (1) Access Channels Access Channels Request-Response Hub Hub Transaction and DB Services Transaction and DB Services Hub Send & Forget (Deferrable)

  12. Hub is a server that routes messages from the sender to the destination Possible actions of the hub: Route the message using message type, message origin, data values in the message, … Reformat the message, add information to the message, split the message to different destinations Multicast or broadcast the message Security checking Monitor the message flow 2 types of hub Hub that handles request-response interaction Hub that routes deferrable messages Possible usages: load balancing, bridging network technologies Disadvantage: additional component implies additional complexity Hub Architecture (2)

  13. Web Services Architecture (1) Loosely coupled web services integration

  14. Web Services Architecture (2) • A cheap form of integration of existing technologies, such as file transfer, COM+, RMI • Suitable for small organizations that have no standardized solutions • Does not require specialized skills of the middleware products • Implemented in large organizations that have islands of integration • Disadvantage: • Slow: all messages are in XML format • Message integrity and web services security must be handled in the web services design

  15. Coupling • Coupling is the degree to which one party to the communication must make assumptions about the other party • The more complex the assumptions, the more tightly coupled the link • Tightly coupled means changes to the interfaces are likely to have effects in the other party

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