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

Vendor Architectures l 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 l Historical vendor architectures: IBM SAA, OSF DCE, OMG OMA, MS DNA l Vendors middleware architectures: the 2 most popular ones: –Microsoft.NET Distributed Architecture –SunSoft J2EE: Java 2 Enterprise Edition

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

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

.NET Framework VBC#C++J#… 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

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

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

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

Middleware Bus Architecture (1) Web Server Voice Server Workstation Server B2B Server Order Entry DeliveryWarehouseBillingAccountsMarketing Middleware

Middleware Bus Architecture (2) l Used in early days distributed systems implementation: middleware software is implemented by the organization l Aim to separate the presentation channels from the business services: middleware provides access to the core services l Either using real-time messages or deferred messages l 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 l Problem: maintenance of the middleware l 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

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

Hub Architecture (2) l Hub is a server that routes messages from the sender to the destination l 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 l 2 types of hub –Hub that handles request-response interaction –Hub that routes deferrable messages l Possible usages: load balancing, bridging network technologies l Disadvantage: additional component implies additional complexity

Web Services Architecture (1) Loosely coupled web services integration

Web Services Architecture (2) l 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 l Disadvantage: –Slow: all messages are in XML format –Message integrity and web services security must be handled in the web services design

Coupling l Coupling is the degree to which one party to the communication must make assumptions about the other party l The more complex the assumptions, the more tightly coupled the link l Tightly coupled means changes to the interfaces are likely to have effects in the other party CouplingPerformance Middleware bus architecture Tightly coupledBest performance Hub architecture Web services architecture Loosely coupledWorst performance