Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Lecture 9: Structured Systems Development MIS 160 Systems Development Life Cycle I

Lecture 9:Structured Systems Development

MIS 160Systems Development Life Cycle I

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004

Structured Development

• Based on the principles of:– top-down decomposition– process driven

• Structured programming

• Structured design

• Structured analysis


Systems Development Life CycleWaterfall Model

Project Identification and Selection

Project Initiationand Planning

Analysis

Logical Design

Physical Design

Implementation

Maintenance

Advantages of Structured Development

• Been used successfully for over 20 years

• Provides a clear framework that defines and divides important activities

• Can be applied to both small and large projects

• Division of labor is easier to facilitate

Limitations of Structured Development

• Specification problems

– assumes that development is a sequential process

• Changing requirements

– requirements specified at the beginning

– assumption that requirements will not change

• Conceptualization and visualization

– document led methodology

– volume of documentation can be huge

• Inaccuracy

– there is only downward trend

Approaches to Structured Development

• Gane and Sarson – uses data flow diagrams– data dictionaries, process descriptions, file

layouts

• Yourdon and DeMarco– similar to Gane and Sarson– difference in the symbols that are used


Data Flow Diagrams

• Process-oriented approach– examines inputs, outputs, and processes of a system– purpose is to show the flow of information through a system

• 4 Sets of DFDs:– Physical DFDs of current system: show how the current system works– Logical DFDs of current system: show what the system currently does– Logical DFDs of proposed system: show what the new system must do– Physical DFDs of proposed system: show how the new system works


Structured Approach Sequence

• Hierarchical Chart

• Physical DFD current system (WHAT/HOW)

• Logical DFD current system (WHAT only)

• Logical DFD proposed system (revised WHAT)

• Physical DFD proposed system (revised WHAT/HOW)


Hierarchical Chart

• Terms:– parent,child,sibling– functional primitive– control module

Hierarchical Chart

Main

1.0 2.0 3.0 4.0 5.0

4.24.1


Data Flow Diagram (DFD)

• Purpose: communication with user

• Components:– external entities (sources, sinks)– processes (subprograms)– data stores (files)– data flows (forms)

Gane & Sarson

processprocess

data storedata store

source/sinksource/sink

data flowdata flow

Yourdon

Data Flow Diagram (DFD) Symbols

Definitions• Process

– The work or action performed on the data

• Data store– data at rest– represents a physical location for a file (e.g., file

folder, computer file)

• Data flow– direction in which data moves– labeled with a name for data in motion

Definitions• Source/sink

– origin (source) of the data– destination (sink) of the data– sometimes referred to as external entities

(outside of the system)

• Do not consider the following– interactions between sources and sinks– what source/ sink does with the information– design/redesign of source/sink– direct access of source/sink to stored data

A Simple Sample

1.0

HospitalPharmacy

System

2.0

ReviewPrescription

Doctor

Prescription

Unfilled Order Info.

Unfilled Response

Prescription

D1 Patient File

Tech Review

PatientInfo

DFD Rules:Processes

• No process can have only outputs. It is making data from nothing (a miracle). If an object has only outputs, it must be a source.

• No process can have only inputs (a black hole). If an object has only inputs, then it must be a sink.

• A process has a verb phrase label.

DFD Rules: Processes

Member

1.0

Member informationRecruit

Members

Black hole

Member

1.0

MembershipRecruit

Members

Miracle

DFD Rules: Data Stores

• Data cannot move directly from one data store to another data store. Data must be moved by a process.

• Data cannot move directly from an outside source to a data store. Data must be moved by a process which receives data from the source and places the data into the data store.

• Data cannot move directly to an outside sink from a data store. Data must be moved by a process.

• A data store has a noun phrase label.

DFD Rules: Data Stores

Member

D2 Memberships

D1 Members

Renewal noticeD2 Memberships

Member Renewal notice D2 Memberships

MembershipInformation

DFD Rules: Sources/Sinks

• Data cannot move directly from a source to a sink. It must be moved by a process if the data are of any concern to our system. Otherwise, the data flow is not shown on the DFD.

• A source/sink has a noun phrase label.

Member Member information Clerk

Context Level

0

DepartmentStaff

Student

FinancialOffice

Course Registration

System

Course Information

Course Information

Course OfferingsFees data

Enrollment InformationSchedule

Level 0

MaintainCourse

Offerings

2.0

MaintainStudent

Enrollment

3.0

CreateReports

DepartmentStaff

Financial Office

Student

Course offering changes

Course offering list

Fee payment history

D1 Course offerings

Available course req.Available courses.

ScheduleCourse enrollment

D2 EnrollmentsCourse enrollment req.Student schedule

Enrollment informationReport request Department

Staff Report

Available courses

Course offerings

Course offerings

D1 Course offeringsCourse information

1.0

Level 1: Process 33.1

ObtainReport Type

D2 Enrollments

DepartmentStaff

3.2

CreateReports

D1 Course offeringsCourse information

Enrollment information

Report request

Report

ReportType

Models and Modeling

• Models are frequently used for documenting functional requirements

– Created during analysis activity phase called ‘define system requirements’

– Focus on events and things

• Models are used in both the traditional and object-oriented approach

Models and Modeling

• Analyst describes information system requirements using a collection of models

• Complex systems require more than one type of model

• Models represent some aspect of the current system/ system being built

Documents

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Lecture 9: Structured Systems Development MIS 160 Systems Development Life Cycle I