Lecture 1: Output/Input Design Structured Systems Development

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MIS 160
Systems Development Life Cycle I
Lecture 9:
Structured Systems Development
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
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
Systems Development Life Cycle
Waterfall Model
Project Identification
and Selection
Project Initiation
and Planning
Analysis
Logical Design
Physical Design
Implementation
Maintenance
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
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
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
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
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
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
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
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
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
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)
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
Hierarchical Chart
• Terms:
– parent,child,sibling
– functional primitive
– control module
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
Hierarchical Chart
Main
1.0
2.0
3.0
4.0
4.1
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
5.0
4.2
Spring 2004
Data Flow Diagram (DFD)
• Purpose: communication with user
• Components:
–
–
–
–
external entities (sources, sinks)
processes (subprograms)
data stores (files)
data flows (forms)
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
Data Flow Diagram (DFD) Symbols
Yourdon
Gane & Sarson
process
data store
source/sink
data flow
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
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
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
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
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
A Simple Sample
1.0
Prescription
Hospital
Pharmacy
System
Tech
Review
Prescription
2.0
Unfilled Order Info.
Doctor
Unfilled Response
Sylnovie Merchant, Ph.D.
Review
Prescription
MIS 160 Section 2
Patient
Info
D1 Patient File
Spring 2004
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.
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
DFD Rules: Processes
1.0
Member information
Recruit
Members
Member
Black hole
1.0
Membership
Recruit
Members
Member
Miracle
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
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.
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
DFD Rules: Data Stores
Member
D1
Renewal notice
D2
Memberships
Members
Membership
Information
D2
Memberships
Renewal notice
Member
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
D2
Memberships
Spring 2004
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
Sylnovie Merchant, Ph.D.
Member information
Clerk
MIS 160 Section 2
Spring 2004
Context Level
Department
Staff
0
Course Information
Course Offerings
Course
Registration
System
Fees data
Financial
Office
Course Information
Student
Sylnovie Merchant, Ph.D.
Enrollment Information
Schedule
MIS 160 Section 2
Spring 2004
Level 0
1.0
Course offering changes
Department
Staff
Course offering list
Course offerings
Maintain
Course
Offerings
Course offerings
D1 Course offerings
Financial
Office
Fee payment history
Course enrollment req.
Student schedule
D2 Enrollments
Enrollment information
Available courses
2.0
Maintain
Student
Enrollment
Available course req.
Available courses.
Course enrollment
Schedule
3.0
Report request
D1 Course offerings
Sylnovie Merchant, Ph.D.
Course information
Student
Create
Reports
MIS 160 Section 2
Report
Department
Staff
Spring 2004
Level 1: Process 3
3.1
Obtain
Report Type
Report request
Report
Type
D1 Course offerings
D2 Enrollments
Sylnovie Merchant, Ph.D.
Course information
Department
Staff
3.2
Enrollment information
Create
Reports
MIS 160 Section 2
Report
Spring 2004
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
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
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
Sylnovie Merchant, Ph.D.
MIS 160 Section 2
Spring 2004
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