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Distributed Data Processing. Topic 3. Outline. Data Processing Network Architecture for DDP Tiered Network Architecture Circuits. Data Processing. Centralized data processing Computer, data, control, staff and processing are centralized Distributed data processing (DDP)
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Distributed Data Processing Topic 3
Outline • Data Processing • Network Architecture for DDP • Tiered Network Architecture • Circuits
Data Processing • Centralized data processing • Computer, data, control, staff and processing are centralized • Distributed data processing (DDP) • May include centralized center plus satellite facilities • Involves distributed computer, data, and processing • Greater flexibility in meeting individual needs • More redundancy and more autonomy
Reasons for DDP • Need for new applications • On large centralized systems, development can take years • On small distributed systems, development can be component-based and very fast • Need for short response time • Centralized systems result in contention among users and processes • Distributed systems provide dedicated resources
Networking Implications • Connectivity requirements • What links between components are necessary? • Availability requirements • Percentage of time application or data is available to users • Performance requirements • Response time requirements
Functions of Data Processing System The work done by any application program can be divided into four general functions: • data storage • data access logic • application logic • presentation logic
Network Architecture “Students list” link in course homepage: Student records Web browser Web Server students.pl Data Storage Presentation Logic Application Logic Data Access Logic Geek (129.118.49.111)
Network Architectures From a viewpoint of distributed application system, there are three fundamental network architectures: • Host-based networks: the host computer performs virtually all of the work • Client-based networks: the client computer performs virtually all of the work • Client-server networks: the work is shared between the hosts and clients
Host-Based Architectures The very first data communications networks were host-based, with the host computer performing all four functions. The clients enabled users to send and receive messages to and from the host computer. This very simple architecture often works very well. Application software is developed and stored on one computer and all data are on the same computer.
Client-Based Architectures In the late 1980s, there was an explosion in the use of microcomputers and microcomputer-based local area networks. Part of this expansion was fueled by a number of low-cost, highly popular applications such as word processors, spreadsheets, and presentation graphics programs.
Client-Based Architectures With client-based architectures, the clients are microcomputers on a local area network, and the host computer is a server on the same network. This simple architecture often works well. However, as the demands for more and more network applications grow, the network circuits can become overloaded.
Client-Based Architectures Example: Novell NetWare 3.12
Client-Server Architectures More organizations today are moving to client-server architectures. Client-Server attempts to balance the processing between the client and the server by having both do some of the processing.
Costs and Benefits of Client-Server Architectures Client-server architectures have some important benefits compared to host-based architectures. • Client-server architectures are scaleable • Client-server architectures can support many different types of clients and servers. • Because no single host computer supports all the applications, the network is generally more reliable.
Client-Server Architectures Client-server architectures also have some critical limitations, the most important of which is their complexity. Even updating the network with a new version of the software is more complicated too. Much of the debate between host- and client-server networks has centered on cost. Microcomputer hardware is more than 1000 times cheaper than mainframe hardware for the same amount of computing power.
Middleware Client-server networks enable software and hardware from different vendors to be used together. Unfortunately, they have few standards. One solution is middleware, software that sits between the application software on both the client and the server. There are dozens of standards for middleware, each of which is supported by different vendors, and each of which provides different functions.
Middleware Middleware does two things: 1. It provides a standard way of communicating that can translate between software from different vendors. 2. It manages the message transfer from clients to servers so that the clients need not know the specific server that contains the application’s data.
Middleware Examples of middleware: • OMG's CORBA (Common Object Request Broker Architecture) • Open Group’s DCE (Distributed Computing Environment) • DCOM (Distributed Component Object Model) • ODBC (Open Database Connectivity) and OLEDB • JDBC (Java Database Connectivity)
Middleware - ODBC Open DataBase Connectivity • A Microsoft’s application development standard • Available on Windows system • Application development environment example: Cold Fusion + ODBC + Any DBMS • A newer version is OLEDB
Middleware - JDBC JDBC is Java's version of the DBI module in Perl 5.
Two-tier, Three-tier, and N-tier Architectures Two-tiered client-server architecture
Two-tier, Three-tier, and N-tier Architectures Three-tiered client-server architecture
N-tier Architectures N-tiered client-server architecture
5-Tier Example IMW’s Forum User Database Updating SQL Server 7.0 NT/IIS BSD/Apache NT/IIS Web Browser NT Web Server FTP Server NT Web Server Database Server Member Forum Member Chicago Austin
Thin Clients versus Fat Clients • Another way of classifying client-server architectures is by examining how much of the application logic is placed on the client. • A “thin client” places little or no logic on the client, and are easier to manage. • A “fat client” places all or almost all of the application logic on the client. • There is no direct relationship between thin/fat clients and 2-/3-/n-tiered architectures.
Network Architecture The function of client computer Thin client/server Presentation Logic Application Logic Client/server Middleware Application Logic Data Access Logic Client-based Data Storage
Network Configuration Network configuration is the basic physical layout of the network. There are two fundamental network configurations: • Point-to-point configuration (or two-point) - sometimes called dedicated circuits. • Multipoint configuration (or multidrop). Most complex computer networks have many circuits, some of each type.
Data Flow Circuits can be designed to permit data to flow in one or both directions. There are three ways to transmit: • Simplex - One way transmission • Half-duplex -Two way communications link, but only one system can talk at a time. • Full duplex -Transmit in both directions simultaneously.
