Systems analysis and design methods 7th whitten and benley chapter 10

Application Architecture & Process Design INFORMATION SYSTEMS FRAMEWORK S S T E A A L Y T S INFORMATION TECHNOLOGY ARCHITECTURE SYSTEM BUILDERS components SYSTEM DESIGNERS specification

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Application Architecture & Process

Design

Introduction

 The chapter will address the following questions:

 What is an information system’s architecture in terms of DATA, PROCESSES, INTERFACES, and NETWORKS — the building blocks of all information systems?

 What are both centralized and distributed computing alternatives for information system design, including various client/server and Internet/intranet options?

 What are the database and data distribution alternatives for

information system design?

 What are the make versus buy alternatives and variations for

information system design?

 What are the user and system interface alternatives for information system design?

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Design

Introduction

 The chapter will address the following questions:

 What are the various networking topologies and their importance

in information system design?

 What are the methods for general application architecture and

design?

 What are the differences between logical and physical data flow diagrams, and explain how physical data flow diagrams are used to model application architecture and guide process design?

 How do you draw physical data flow diagrams for a

system/application?

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Design

General System Design

 During general systems design the basic technical

decisions are made These decisions include:

 Will the system use centralized or distributed?

 Will the system’s data stores be centralized or distributed? If

distributed, how so? What data storage technology(s) will be used?

 Will software be purchased, built in-house, or both? For programs

to be written, what technology(s) will be used?

 How will users interface with the system? How will data be input? How will outputs be generated?

 How will the system interface to other, existing systems?

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Design

General System Design

 The decisions made during general systems design

constitute the application architecture of the system

 An application architecture defines the technologies to be used

by (and to build) one, more, or all information systems in terms of its data, process, interface, and network components It serves as a framework for general design

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Design

INFORMATION SYSTEMS FRAMEWORK

S S T E A A L Y T S

INFORMATION TECHNOLOGY ARCHITECTURE

SYSTEM BUILDERS (components)

SYSTEM DESIGNERS (specification)

SYSTEM USERS (requirements)

SYSTEM OWNERS (scope)

Database Architecture

Database Scehma

Data Requirements

Business Subjects

FOCUS ON SYSTEM DATA

Application Schema

Business Processes

Business Functions

FOCUS ON SYSTEM PROCESSES

Interface Schema

Interface Requirements

System Context

FOCUS ON SYSTEM INTERFACES

Processor and Software Architecture

Interface Architecture Networking

Architecture

Network Schema Communication Reqts.

Operating Locations

FOCUS ON SYSTEM GEOGRAPHY

Architecture Project or

Implementation Phase

(deliver the new system into operation)

Study Phase

(establish system improvement objectives)

Survey Phase

(establish scope and project plan)

System Development

C US TOMER cus tom e r-no cus tom e r-na m e cus tom e r-ra ting

ba la nce - due

PR ODUC T product-no product-na m e unit- of-m e a s ure unit- price qua ntity-a va ila ble

OR DER orde r- no orde r- da te products -orde re d qua ntitie s -orde re d

Order Form Help +

Customer Form

P roduct Lookup

Logon New Customer New O rder

O rder Accepted Change

of Address

Marketing Advertising Orders Sales Cancellations Services

O rder

M ana ge ment System

Custome r

Accounts

R eceiv able Databas e Warehouse

Ba nk

O rder P ic king

O rder Credit

Credit Voucher

Check credit Validate customer Validate Releas e order

Cus tomers Orders Products order customer number valid order order without vali d customer

credit order with valid products approved order

quantity approved order rejected order

prices pic ki ng tick et

EDI St

Louis HQ

LA Office Indy Ware- NY

O ffice

West Customers Customers East

Mai ntenance

R ecords

P roducts Catal og

order catal og changes ship ship ship order credit credit service

CUSTOMER customer_no [Alpha (1 0)] INDEX customer_name [Alpha(32)]

customer_rating [Alpha(1)] INDEX balance_due [R eal(5 ,2)]

P R ODUCT product_no [Alpha(10)] INDEX product_name [Alpha(32)]

unit_of_measure [Alpha(2)]

unit_price [R eal(3,2)]

quantity_available [Integer(4)]

OR DER order_no [Alpha(1 2)] INDEX order_date [Date(mmddyyyy) CUSTOMER customer_no

OR DER _P R ODUCT

OR DER order_no

P R ODUCT.product_no quantity_ordered [Integer(2)

Ch ec k

P ro d uc t

Da ta

Ch ec k Cre d it Data

NT Server LA

NT Serv er NY

Communications Controller

P BX

Enternet LAN AIX/Lan

M anager Ethe rne t LAN/NT Etherne t LAN/NT Clie nt P C Clie nt P C Client P C Client P C

Fi r ecr acker Sal es

Database Decisions

Process Decisions

Interface Decisions DecisionsNetwork

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Design

Information Technology

Architecture

 Network Architectures for Client/Server Computing

 What is client/server computing?

 A client is single-user computer that provides (1) user interface

services, appropriate database and processing services; and (2) connectivity services to servers (and possibly other clients).

 A server is a multiple-user computer that provides (1) shared

database, processing, and interface services; and (2) connectivity to clients and other servers.

 In client/server computing an information system’s database,

software, and interfaces are distributed across a network of clients and servers which communicate and cooperate to achieve system

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Design

Architecture

 Client/server computing is an alternative to traditional centralized computing

 In centralized computing, a multi-user computer (usually a

mainframe or minicomputer) hosts all of the information system components including (1) the data storage (files and databases), (2) the business logic (software and programs), (3) the user interfaces (input and output), and (4( any system

interfaces (networking to other computers and systems) The user may interact with this host computer via a terminal (or, today, a PC emulating a terminal), but all of work is actually done on the host computer

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All business logic is programmed

to execute on the server.

Resulting data files may be transferred to another server across the network.

All data is stored on the server and all file and database access and update commands and instructions are executed on the server computer.

Centralized Computing

Resulting data files may be transferred to another server across the network.

Distributed Presentation Computing

The user interface (usually graphical) is stored and executed

on the client.

to execute on the client using a PC-based programming language.

A database server is usually microprocessor-based (e.g., UNIX

or Windows/NT Server) but could

still be a mainframe or minicomputer.

Distributed Database Computing

on the client.

Some business logic may be programmed to execute on the client.

Most business logic is programmed

Typically data and business logic (and possibly other services) are

on separate servers (same OS's as

in previous column).

Distributed Data/Logic Computing

User interfaces may be stored and executed on the client, or downloaded from the Internet or

Appropriate business logic may be downloaded from Inter/intranet server to execute on the client.

Appropriate business logic is programmed to execute on the server.

All data is stored on the server (possibly multiple servers) and all file and database access and update commands and instructions are executed on the server computers.

Utilizes data and/or file servers as

in previous two columns, but adds one or more Internet and intranet servers.

Internet/Intranet Computing

The server is usually a

minicomputer (e.g., OS/400 OS) or mainframe computer (e.g MVS,

VM, or UNIX OS).

Wide Area Network

Local Area Network

on the client.

All data is stored on the server (possibly multiple servers) and all file and database access and update commands and instructions are executed on the server computers.

Intranet or Internet Local or

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 The user interface (or presentation) is distributed off the server and onto the client

 All other elements of the centralized application remain on the

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 Distributed presentation computing advantages:

• It can be implemented relatively quickly since most aspects of the

legacy application remain unchanged.

• Users get a friendly and familiar interface to existing systems

• The useful lifetime of legacy applications can be extended until such a time as resources warrant a wholesale redevelopment of the application.

 Distributed presentation computing disadvantages:

• The application’s functionality cannot be significantly improved,

and the solution does not maximize the potential of the client’s desktop computer by only dealing with the user interface.

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 Sometimes called two-tiered client/server.

 This architecture places the information system’s stored data on a server, and the business logic and user interfaces on the clients

 A local or wide area network usually connects the clients to the server

PCs) connected to one or more server computers (usually microprocessor-based, but could also include mainframes or minicomputers) through cable over relatively short distances.

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• File servers store the database, but the client computers must

execute all database instructions This means that entire databases and tables may have to be transported to and from the client across the network

• Database servers also store the database, but the database

commands are also executed on those servers The clients merely send their database commands to the server The server only

returns the result of the database command processing — not entire databases or tables Thus, database servers generate much less network traffic

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 Distributed data computing advantages:

• Separates data and business logic to (1) isolate each from changes

to the other, (2) make the data more available to users, and (3) retain the data integrity of centralized computing through centrally managed servers.

 Distributed data computing disadvantages:

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Design

Architecture

 Referred to as three-tiered or n-tiered client/server computing.

 This approach distributes databases and business logic to

separate servers

 Uses the same database server(s) as in the two-tiered approach

 Uses an application server

manage transactions.

from the client to the application server.

 Only the user interface and some relatively stable or personal business logic need be executed on the clients

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Design

Architecture

 Distributed data and logic computing disadvantages:

• Very complex to design and development.

• The most difficult aspect of three-tier client/server application design is partitioning.

– Partitioning is the act of determining how to best distribute or

duplicate application components (data, process, and interfaces) across the network.

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Design

Architecture

 The Internet is an (but not necessarily ‘the’) information

superhighway that permits computers of all types and sizes, all over the world to exchange data and information using

standard languages and protocols

 An intranet is a secure network, usually corporate, that uses

Internet technology to integrate desktop, workgroup, and enterprise computing into a single cohesive framework

• The intranet provides management and users with a common

interface to applications and information

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Design

Architecture

specifically to exploit the Internet standards

• Java applets (modular software components) are stored on an

Internet or intranet server and downloaded to the client when they access the application

• Java applets can execute on any client computing platform

 A network computer (or NC) is designed to only run

Internet-based applications (such as web browsers and Java applets).

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Design

Architecture

 The well designed network provides connectivity and interoperability

• Connectivity defines how computers are connected to “talk” to

one another.

• Interoperability is an ideal state in which connected computers

cooperate with one another in a manner that is transparent to their users (the clients).

• Network topology describes how a network provides connectivity

between the computers on that network.

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Design

Data and DB process on server

All business logic on the mainframe server

All data on the mainframe server

Business logic on application server

User Interface

on the PC Client Network

Logic & user interface on PC Network

server

Internal user interface on PC Network

Secure intranet provides access

to data, logic, and interfaces

Distributed Presentation

Distributed Data (2-tier)

Distributed Data & Logic (3-tier)

Internet and Intranet

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Design

Architecture

 The Bus network topology:

• A direct point-to-point link between any two computer systems.

• The simplest network topology.

• The network can contain mainframes, minicomputers (or

mid-range computers), personal computers, and dumb and intelligent terminals

• To completely connect all points between n computers, you would

need n times (n-1)/2 direct paths

• Only one computer can send data through the bus at any given

time

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Design

Architecture

• Connects multiple computers and some peripherals into a ring-like

structure.

• Each computer can transmit messages, instructions, and data (called

packets) to only one other computer (or node on the network)

• Every transmission includes an address

• When a computer receives a packet, it checks the address and if the

packet’s address is different than the computer’s address, it passes it

on to the next computer or node

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Design

Architecture

 The Star network topology:

• Links multiple computer systems through a central computer.

• The central computer does not have to be a mainframe or minicomputer

• Central computer could be an application server that manages the transmission of data and messages between the other clients and servers (as in the n-tier model).

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Design

Architecture

 The Hierarchical network topology:

• Can be thought of as a multiple star network, where the

communications processors are arranged in a hierarchy.

• The top computer system (usually a mainframe) controls the entire

network

 All network topologies operate according to established network protocols that permit different types of computers to communicate and interoperate

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• A relational database stores data in a tabular form Each file is

implemented as a table Each field is a column in the table Each records in the file is a row in the table Related records between

two tables are implemented by intentionally duplicating columns

in the two tables.

• A distributed relational database distributes or duplicates tables

to multiple database servers (and in rare cases, clients).

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 The software required to implement distributed relational

databases is called a distributed relational database management

system.

distributed RDBMS) is a software program that controls

access to, and maintenance of the stored data It also provides for backup, recovery and security It is sometimes called a

client/server database management system.

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 The database engine is that part of the DBMS that executes

database commands to create, read, update, and delete records (rows) in the tables

• In a PC RDBMS, the database engine that processes all database commands must execute on the client PC, even if the data is actually stored on the server

• In a distributed RDBMS, the database engine that processes all

database commands executes on the database server.

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Design

Architecture

 Data Architectures for Distributed Relational Databases

 True data distribution partitions data to one or more database

servers

 Entire tables can be allocated to different servers, or subsets of rows in a table can be allocated to different servers

 An RDBMS controls access to and manages each server

 Entire tables can be duplicated on different servers, or subsets of rows in a table can be duplicated to different servers

 The RDBMS not only controls access to, and management of

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• The batch inputs are processed against master files or databases.

• Transaction files or databases may also be created or updated by

the transactions

• Most outputs tend to be generated to paper or microfiche on a

scheduled basis

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 The majority of systems have slowly evolved from batch

processing to on-line processing

 On-line systems provide for a conversational dialogue between user and computer

 Business transactions and inquiries are often best processed when they occur

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 Distributed on-line computers handle data input and editing

 Edited transactions are collected into a batch file for later transmission to host computers that process the file as a batch

 Results are usually transmitted as a batch back to the original computers

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 Keying errors have always been a major source of errors in computer inputs (and inquiries)

 In batch systems, keying errors can be eliminated through optical character reading (OCR) and optical mark reading (OMR) technology

 The real advances in keyless data entry are coming for on-line

systems in the form of auto-identification systems.

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 Some businesses use this technology for remote data collection

• For example, UPS.

 A promising technology is emerging in the form of handheld

PCs (HPCs)

• Similar to personal organizers and personal data assistants, these

HPCs offer greater compatibility with desktop and laptop PCs

• Based on Microsoft’s Windows CE operating system, they can be

programmed to become disconnected clients in a client/server application

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 GUI technology has become the user interface of choice for client/server applications

 GUIs do not automatically make an application better

 Poorly designed GUIs can negate the alleged advantages of consistent user interfaces

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 Most users interface with the Internet via a client software tool

called a browser

• The browser paradigm is based on hypertext and hyperlinks

– Hypertext are keywords that are clearly highlighted as a link to

a new page of information

– Hyperlinks are links from graphics, buttons, and areas that link

to a different page of information.

• These links may it easy to navigate from page-to-page and

application-to-application.

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 Information systems are being designed to directly incorporate the electronic mail

• For example, Microsoft Outlook and Exchange Server and

IBM/Lotus Notes allow for the construction of intelligent

electronic forms that can be integrated into an application

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 Businesses that operate in many locations and businesses that seek more efficient exchange of transactions with their suppliers and/or customers often utilize electronic data interchange

business transactions between customers and suppliers.

 With EDI, a business can eliminate its dependence on paper documents and mail, plus dramatically reduce response time

 Various EDI standards exist for the standardized exchange of data between organizations within the same industry

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 Similar to EDI except that the actual images of forms and data are transmitted and received

 It is particularly useful in applications in which the form images or graphics are required (insurance industry)

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information systems (and computer systems) interoperate.

 A key technology used to interface and integrate systems is

middleware

with incompatible technologies Middleware serves as a consistent bridge between two or more technologies It may be built into operating systems, but it is also frequently sold as a separate product

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 The preferred or approved user and system interface technologies may be specified as part of the Interface architecture

 An organization may leave interface technologies as a decision

to be made on a project-by-project basis

 An organization may establish macro guidelines for interfaces and leave the micro decisions to individual projects

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