Lecture 8

Centralized Systems

a central, multi-user computer hosts all the DATA, PROCESS, and INTERFACE components of an information system. User interact with the system via terminals (or terminals emulators)

File Sever Disadvantages

- Frequency excessive network traffic to transport data between server and clients. - Client must fairly robust ("fat") because it does most of the work. -Database integrity can be easily compromised.

Distributed Data (Client/server system) is a solution in which

1) the data and data manipulation layers are placed on the server(s). 2) The application logic, presentation logic, and presentation layers, are placed on the clients. (Also called *** Two-tiered client/server*** computing)

Distributed data and application ( client/server system)

1) the data and data manipulation layers are placed on their own server(s). 2) the application logic is placed on its own server, 3) the presentation logic and presentation layers are placed on the clients. Also called **** Three or n-tiered clients/server computing.

Distributed System

DATA, PROCESS, and INTERFACE components of an information systems are distributed to multiple locations in a computer network. Accordingly, the processing workload is distributed across the network.

Local Area Network (LAN)

Is a set of client computers (PCs) connected to one or more server computers either through cable or wireless connection over relatively (short distances).

System Analysis vs System Design

System analysis emphasizes on the business problem, (WHAT) whereas system design emphasizes on the technical or implementation concerns of the system (HOW).

System Design

Tasks that focus on the specification of a detailed computer-based solution (also called physical design).

Design unit

a self-contained collection of processes, data stores, and data flows that share similar design characteristics.

Vertical partitioning

assigns different columns to different servers.

Horizontal partitioning

assigns different rows to different servers.

Distributed relational database

distributes or duplicates tables to multiple database servers located in geographically important locations.

Data replication

duplicates some or all tables (or parts of tables) on more than one database server. Database technology controls access to, and manages consistency of duplicated data across the servers.

File Server System

is a LAN- based solution in which a server hosts only the data layers of an information system. All other layers are implemented on the client computers.

Network computing system

is a multi-tiered solution in which the presentation and presentation logic layer are implemented in client-side web browser using content downloaded from a web server. The presentation logic layer then connects to the application logic layer running on the application server, which subsequently connects to the database servers on the backside of the system.

Fat Client

is a personal computer or workstation that has typically more powerful processor speed, memory, and storage capacity. It has software applications to process data at the client site.

Thin Client

is a personal computer that does not have a very powerful processor speed and memory because it only presents the user interface to the user.

Intranet

is a secure network usually corporate, that uses internet technology to integrate desktop, and enterprise computing into a cohesive framework.

Distributed Presentation (client/server system)

is a solution in which the presentation and presentation logic layers only are shifted from the server to reside on the client.

Client/ Server System

is a solution in which the presentation, presentation logic, application logic, data manipulation, and data layers are distributed between client PCs and one or more servers.

Physical Process

is either a processor, such as computer or person, or a technical implementation of specific work to be performed, such as a computer program or manual process.

Physical data flow diagram (DFDs)

model the technical and human decision to be implemented as part of an information system (HOW, BY WHOM)

Application Architecture

specifies the technologies to be used to implement one or more (and possibly all) information system in terms of DATA, PROCESS, and INTERFACE, and how these components interact across a network. It serves as a outline or blueprint for detailed design and implementation.

Relational database

stores data in a tabular form. Each file is implemented as a table. Each field is a column in the table. Related records between two tables are implemented by intentionally duplicated columns in the two tables. (Primary and Foreign Keys)

Data partitioning

truly distributes rows and columns of tables to specific database servers with little or no duplication between servers.

Client/ Server Architecture

► Client/server system - Thin Client - Fat Client

Distributed Computing Layers

►(Interface) - Presentation Layer- the user interface/ - Presentation layer logic- such as input editing. ►(Process) -Application logic layer- the business rules, policies, and procedures. ►(Data) -Data manipulation layer- to store and retrieve data to and from the database. - Data layer- the actual business data.

Database Distribution

►Data partitioning - Vertical Partitioning -Horizontal Partitioning ► Data Replication

Interface Architectures

◙ Batch inputs and outputs ◙ On-line inputs and outputs ◙ Remote batch ◙ Keyless data entry (and automatic identification) ◙ Pen input ◙ Electronic Data Interchange (EDI) ◙ Middlewar (BizTalk)

Client/ Server Architecture

◙ Database server ◙ Transaction server ◙ application server ◙ messaging or groupware server ◙ web server

Design Tasks of an In-House Project

◙ Design the application architecture -Defines the technologies to be used and used to build. - Physical Data Flow Diagram ◙ Design the System Databases -Database schema (Data Dictionary) ◙ Design the System Interface -User interfaces: input, output, and dialogue specifications. -Prototypes ◙ Package Design Specifications -Specifications to guide programmers ◙ Update Project Plan -Modified Budget/ Schedule

File Server Architecture

◙ Local Area Network (LAN) ◙ File Server Sytem

Why Distributed Systems:

◙ Modern businesses are already decentralized and distributed. ◙ Distributed computing moves information and services closer to the customers and users who need them. ◙ Distributed computing consolidates the power of personal computers across the enterprise. ◙ Distributed computing solutions are more user-friendly because they utilize the PC as the end user interface. ◙ Personal computers and network servers are cheaper than centralized mainframe computers.

Internet and Intranet based Architecture

◙ Network computing system ◙ Intranet

Physical Data Flow (Represents)

◙ The planned implementation of an input to, or output from a physical process. ◙ Database command / action such as create, read, update, or delete. ◙ The flow of data between to modules or subroutines (represented as physical processes) in a program.