Post on 25-Dec-2015
PHASE 23
SYSTEMS ANALYSIS & DESIGN 3E
Objectives
Explain the structured analysis process and identify its elements
Describe the symbols used in data flow diagrams and explain the rules for their use
Explain the sequence of data flow diagrams, from general to specific, and what each data flow contains
PHASE 24
SYSTEMS ANALYSIS & DESIGN 3E
Objectives
Explain how to level and balance a set of data flow diagrams
Draw a complete set of data flow diagrams for an information system
Describe how a data dictionary is used and what it contains
PHASE 25
SYSTEMS ANALYSIS & DESIGN 3E
Objectives
Demonstrate the use of structured English, decision tables, and decision trees to develop information system process descriptions
Explain the relationships among data flow diagrams, the data dictionary, and process descriptions
PHASE 26
SYSTEMS ANALYSIS & DESIGN 3E
Systems analysis phase has three stages Requirements determination (Chapter 3) Requirements analysis (Chapter 4) Evaluation of alternatives (Chapter 5)
Introduction
PHASE 27
SYSTEMS ANALYSIS & DESIGN 3E
Structured Analysis
Examines inputs, outputs, and processes Common method Process-centered technique Uses three main tools
Data flow diagrams (DFDs) Data dictionary Process descriptions
Tools can be applied using computer-aided software engineering (CASE) tools
PHASE 28
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
Data flow diagrams (DFDs) are graphical aids that describe an information system
DFDs represent a logical model that shows what a system does, not how it does it
PackageClick to see Figure 4-1
PHASE 29
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
Data flow diagram symbols Four basic symbols
Process Data flow Data store External entity
Two popular symbol sets Gane and Sarson Yourdon
PackageClick to see Figure 4-2
PHASE 210
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
Process symbol Symbol is a rectangle with rounded
corners Documented with process descriptions Receive input data and produces output Output has a different form, or content,
or both Details are shown in a process
description In DFDs the process symbol appears as a
black box, underlying details not shown
PHASE 211
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
Data flow symbol Symbol is a line with an arrowhead
showing direction A path for data to move from one part of
the system to another Might represent one or many pieces of
data At least one data flow must enter and exit
each process
PackageClick to see Figure 4-3
PHASE 212
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
Data flow symbol Incorrect process and data flow
combinations cause problems Spontaneous generation (miracle) Black hole Gray hole
PackageClick to see Figure 4-4
PHASE 213
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams Data store symbol
Symbol is a rectangle open on the right side Data store also is called a data repository Represents data that is retained for later
processing Must be connected to a process with a data
flow Must have at least one outgoing and
incoming data flow
PackageClick to see Figure 4-6
PackageClick to see Figure 4-5
PHASE 214
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
External entity symbol Symbol is a square, usually shaded Represents a person, organization, or
other system that provides data or receives output from the system
External entities are called terminators Source (supplies data to the system) Sink (receives data from the system)
PackageClick to see Figure 4-8
PackageClick to see Figure 4-7
PHASE 215
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
External entity symbol Symbol is a square, usually shaded Represents a person, organization, or
other system that provides data or receives output from the system
External entities are called terminators Source (supplies data to the system) Sink (receives data from the system
Must follow specific rules for connecting DFD symbols
PackageClick to see Figure 4-9
PHASE 216
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
Context diagrams Top-level view that shows the overall
boundaries of the system Represent the results of fact-finding One process symbol, numbered 0 (zero) is
drawn in the center Data flows connect the process to the entities Abbreviated symbols can be used to identify
entities
PackageClick to see Figure 4-11
PackageClick to see Figure 4-10
PHASE 217
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
Conventions for data flow diagrams Each context diagram must fit on one page Process name in the context diagram should
be the name of the information system Use unique names within each set of
symbols Do not cross lines Use abbreviated identifications Use a unique reference number for each
process symbol
PackageClick to see Figure 4-12
PHASE 218
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
Diagram 0 Displays more detail than the context
diagram Shows entities, major processes, data flows,
and data stores
PackageClick to see Figure 4-13
PHASE 219
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams Shows entities, major processes, data
flows, and data stores Other characteristics
Can contain diverging data flows Exploded (partitioned or
decomposed) version of process 0 Diagram 0 is the child of the parent
context diagram Also can be called an overview or
level 0 diagram Can contain functional primitives
PackageClick to see Figure 4-15
PackageClick to see Figure 4-14
PHASE 220
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
Lower-level diagrams Usually necessary to show more detail
PackageClick to see Figure 4-16
PHASE 221
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
Lower-level diagrams Usually necessary to show more detail Design must consider
Leveling Balancing Data stores
PackageClick to see Figure 4-17
PHASE 222
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
Leveling Process of drawing increasingly detailed
diagrams Also called exploding, partitioning, or
decomposing
PackageClick to see Figure 4-18
PHASE 223
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
Balancing Maintains consistency among an entire
set of DFDs Parent’s input and output data flows are
preserved on the child
PackageClick to see Figure 4-19
PHASE 224
SYSTEMS ANALYSIS & DESIGN 3E
Data Flow Diagrams
Data stores Might not appear on higher-level DFDs Are shown on the the highest-level DFD
that has two or more processes using that data store
PackageClick to see Figure 4-20
PHASE 225
SYSTEMS ANALYSIS & DESIGN 3E
TRADEOFF
Which technique is better: top-down or bottom-up? Most analysts start at the top
Draw the context diagram Diagram 0 and lower-level diagrams next
Others start at the bottom Identify functional primitives, data stores,
external entities, and data flows Work up until diagram 0 is reached
Results must be clear and easily understood
PackageClick to see Figure 4-23
PackageClick to see Figure 4-21
PHASE 226
SYSTEMS ANALYSIS & DESIGN 3E
A KEY QUESTION
Based on the rules in the text, how many problems do you see in Figure 4-22?
PackageClick to see Figure 4-22
PHASE 227
SYSTEMS ANALYSIS & DESIGN 3E
Data Dictionary
Also called data repository Documents specific facts about the system
Data flows Data stores External entities Processes Data elements (data items, fields) Records (data structures)
PackageClick to see Figure 4-24
PHASE 228
SYSTEMS ANALYSIS & DESIGN 3E
Data Dictionary
Using CASE tools to document the system Can help create and maintain a data
dictionary Various tools are available
Visible Analyst is a popular example Key objective is to provide clear,
comprehensive information about the system
PHASE 229
SYSTEMS ANALYSIS & DESIGN 3E
Data Dictionary
Documenting the data elements Must document every data element
PackageClick to see Figure 4-25
PHASE 230
SYSTEMS ANALYSIS & DESIGN 3E
Data Dictionary
Documenting the data elements Must document every data element Standard form or CASE tool can be used All major characteristics must be recorded
and described
PackageClick to see Figure 4-26b
Package
Click to see Figure 4-26a
PHASE 231
SYSTEMS ANALYSIS & DESIGN 3E
Data Dictionary
Documenting the data flows Must document every data flow Standard form or CASE tool can be used All major characteristics must be recorded
and described
PackageClick to see Figure 4-27
PHASE 232
SYSTEMS ANALYSIS & DESIGN 3E
Data Dictionary
Documenting the data stores Must document every data store Standard form or CASE tool can be used All major characteristics must be recorded
and described
PackageClick to see Figure 4-28
PHASE 233
SYSTEMS ANALYSIS & DESIGN 3E
Data Dictionary
Documenting the processes Must document every process Standard form or CASE tool can be used All major characteristics must be recorded
and described
PackageClick to see Figure 4-29
PHASE 234
SYSTEMS ANALYSIS & DESIGN 3E
Data Dictionary
Documenting the external entities Must document every external entity Standard form or CASE tool can be used All major characteristics must be recorded
and described
PackageClick to see Figure 4-30
PHASE 235
SYSTEMS ANALYSIS & DESIGN 3E
Data Dictionary
Documenting the records Must document every record Standard form or CASE tool can be used All major characteristics must be recorded
and described
PackageClick to see Figure 4-31
PHASE 236
SYSTEMS ANALYSIS & DESIGN 3E
Data Dictionary
Data dictionary reports Data dictionary is a central storehouse for
documentation Using this data, you can produce many
valuable reports
PHASE 237
SYSTEMS ANALYSIS & DESIGN 3E
Process Description Tools
Process description documents a functional primitive, using modular design
Modular design uses three logical structures Sequence Selection Iteration
PHASE 238
SYSTEMS ANALYSIS & DESIGN 3E
Process Description Tools
Structured English Subset of standard English
PackageClick to see Figure 4-32
PHASE 239
SYSTEMS ANALYSIS & DESIGN 3E
Process Description Tools
Structured English Subset of standard English Describes process logic
Use only standard sequence, selection, and iteration structures
Use indentation for readability Use a limited vocabulary
PackageClick to see Figure 4-33
PHASE 240
SYSTEMS ANALYSIS & DESIGN 3E
Process Description Tools
Decision tables Show a logical structure that describes process
logic Every logical combination is shown initially Results then can be combined and simplified Programmers can use decision tables in
developing code
PackageClick to see Figure 4-36
PackageClick to see Figure 4-34
PackageClick to see Figure 4-35
PHASE 241
SYSTEMS ANALYSIS & DESIGN 3E
Process Description Tools
Decision trees Graphical representation that shows a decision
table’s conditions, actions, and rules Logic structure is shown horizontally Easy to construct and understand Decision table is better in complex situations
PackageClick to see Figure 4-38
PackageClick to see Figure 4-37
PHASE 242
SYSTEMS ANALYSIS & DESIGN 3E
TRADEOFF
Logical vs. physical models Relationship between physical and logical
models: first study facts, then logical analysis Four-model approach offers many advantages
Physical model of current system Logical model of current system Logical model of new system Physical model of new system
Four-model approach can be time-consuming and expensive
PHASE 243
SYSTEMS ANALYSIS & DESIGN 3E
A KEY QUESTION
Is it proper to consider physical implementation questions during the systems analysis phase?
Is Rick going off on a tangent? What are the issues?
PHASE 244
SYSTEMS ANALYSIS & DESIGN 3E
SOFTWEAR, LIMITED
The SWL team completed the fact-finding process
Rick and Carla are ready to prepare a logical model of the system
PHASE 245
SYSTEMS ANALYSIS & DESIGN 3E
SOFTWEAR, LIMITED
Data flow diagrams Rick and Carla prepared a draft context
diagram
PackageClick to see Figure 4-39
PackageClick to see Figure 4-40
PHASE 246
SYSTEMS ANALYSIS & DESIGN 3E
SOFTWEAR, LIMITED
Data flow diagrams Rick and Carla prepared a draft context
diagram Various revisions resulted in final version
PackageClick to see Figure 4-41
PHASE 247
SYSTEMS ANALYSIS & DESIGN 3E
SOFTWEAR, LIMITED
Data flow diagrams Rick and Carla prepared a draft context
diagram Various revisions resulted in final version Next steps
Analysts prepared diagram 0
PackageClick to see Figure 4-42
PHASE 248
SYSTEMS ANALYSIS & DESIGN 3E
SOFTWEAR, LIMITED
Data flow diagrams Rick and Carla prepared a draft context
diagram Various revisions resulted in final version Next steps
Analysts prepared diagram 0 Rick partitioned the ESIP subsystem Carla developed other lower-level
diagrams Logical model was completed Physical design issues were considered
PackageClick to see Figure 4-43
PHASE 249
SYSTEMS ANALYSIS & DESIGN 3E
SOFTWEAR, LIMITED
Data dictionary and process descriptions Rick and Carla’s activities
Documented the ESIP subsystem Met with Amy Calico to review the final
model
PackageClick to see Figure 4-44
PackageClick to see Figure 4-45
PackageClick to see Figure 4-46
PackageClick to see Figure 4-47
PackageClick to see Figure 4-48