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Systems Analysis & Design(Sixth Edition)
Chapter 4Data and Process Modeling
PHASE 2: SYSTEMS ANALYSIS
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Chapter Objectives
Describe data and process modeling concepts and tools, including data flow diagrams, a data dictionary, and process descriptions
Describe the symbols used in data flow diagrams and explain the rules for their use
Draw data flow diagrams in a sequence, from general to specific
Explain how to level and balance a set of data flow diagrams
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Chapter Objectives
Describe how a data dictionary is used and what it contains
Use process description tools, including structured English, decision tables, and decision trees
Describe the relationship between logical and physical models
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Introduction
In Chapter 4, we will use data and process modeling techniques …
To develop a logical model of the proposed system Logical model WHAT system must do Physical model HOW system will be constructed (later
in systems design phase) To document system requirements
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OverviewData and Process Modeling Tools
Systems analysts use many graphical techniques to describe an information system
A data flow diagram (DFD) uses various symbols to show how the system transforms input data into useful information
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Data Flow Diagrams
A data flow diagram (DFD) shows how data moves through an information system but does not show program logic or processing steps
A set of DFDs provides a logical model that shows what the system does, not how it does it
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Data Flow DiagramsDFD Symbols
DFDs use four basic symbols that represent processes, data flows, data stores, and entities
Gane and Sarson symbol set Yourdon symbol set
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Data Flow DiagramsDFD Symbols
PROCESS symbol Receives input data and produces output that has a
different content, form, or both Contains the business logic business rules Referred to as a black box
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Data Flow DiagramsDFD Symbols
DATA FLOW symbol Represents one or more data items The symbol is a line with a single or double arrowhead
Fork same data
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Data Flow DiagramsDFD Symbols
Basic rules for all PROCESSES and DATA FLOWS At least 1 data flow must enter and 1 data flow must exit
each process
AVOID: Spontaneous generation
Has no input Black hole
Produces no output Gray hole
Input insufficient to generate output
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Data Flow DiagramsDFD Symbols
DATA STORE symbol Represent data that the system stores Physical characteristics of data store are unimportant
Concerned only with logical model
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Data Flow DiagramsDFD Symbols
Basic rules for all DATA STORES
Data cannot be moved from one store to another Data cannot move from an outside source to a data store Data cannot move directly from a data store to a data sink
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Data Flow DiagramsDFD Symbols
ENTITY Symbol Symbol is a rectangle Depicts origin and/or destination of data Sometimes referred to as external entity Name of the entity appears inside the symbol
AKA: Terminators final destination Source supplies data Sink receives data
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Data Flow DiagramsDFD Symbols
Basic rules for all ENTITIES (i.e. sources/sinks)
Entity must be connected to a process by a data flow and not directly to a data store
Data cannot move directly from a source to a sink
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Data Flow Diagrams
Basic rules for connecting processes, data stores, and entities in a DFD
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Creating a Set of DFDs
Create a graphical model of the information system based on your fact-finding results
Performing three main tasks Step 1: Draw a context diagram Step 2: Draw a diagram 0 DFD Step 3: Draw the lower-level diagrams
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Creating a Set of DFDs1. Draw a Context Diagram
Process 0represents
system
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Creating a Set of DFDs Draw a Context Diagram
Context Drawing Guidelines (Page 156, Figure 4-13) Fit on one page Name of information system Process name Use unique names within each set of symbols Do not cross lines Obtain user input and feedback
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Creating a Set of DFDsContext Diagram
Refer to Figure 4-13 on page 156 of textbook What is the name of the system in this Context Diagram? How many sources of data are there? What are they? Which entities (sinks) do not supply inputs to the Order
System? What data is going into the Order System from Customer? What data is going to the Warehouse from the Order
System?
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Creating a Set of DFDs Draw a Level-0 DFD Diagram
2. Draw a Level-0 Diagram
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Creating a Set of DFDs Draw a Level-0 DFD Diagram
Level-0 DFD Drawing Guidelines (p. 161, Figure 4-16) Decomposition of Context diagram Parent/Child diagram
KEEP all data flows into and out of process 0 KEEP all entities
Functional primitive Diverging data flow – different locations
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Creating a Set of DFDs Draw Lower Level 1-n DFD Diagrams
Level 1-N Diagrams
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Creating a Set of DFDs Draw Lower Level 1-n DFD Diagrams
Level 1-n DFD Drawing Guidelines Leveling Balancing
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Creating a Set of DFDs Draw a Level-0 DFD Diagram
2. Draw a Level-0 Diagram
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Creating a Set of DFDs Draw Lower Level 1-n DFD Diagrams
Level 1-N Diagrams
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Data Dictionary
Central Storehouse (aka Data Repository)
Facts about system Data elements (aka Field) Record (aka Data Structures)
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Data Dictionary Documenting the Data Elements
Objective:Provide clear, comprehensive information about the data and processes that make up the system
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Data Dictionary Documenting the Data Elements
The following attributes are recorded and described: Data element name or label Alias Type and length Default value Acceptable values - Domain and validity rules
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Data Dictionary Documenting the Data Elements
The following attributes are recorded and described: Source Security Responsible user(s) Description and comments
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Data Dictionary Documenting the Data Flows
Typical attributes of data flows: Data flow name or label Description Alternate name(s) Origin Destination Record Volume and frequency
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Data DictionaryDocumenting the Data Stores
Typical attributes of a data store:
Data store name or label Description Alternate name(s) Attributes Volume and frequency
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Data Dictionary Documenting the Processes
Typical attributes of a process:
Process name or label Description Process number Process description
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Data Dictionary Documenting the Entities
Typical attributes of an entity:
Entity name Description Alternate name(s) Input data flows Output data flows
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Data Dictionary Documenting the Records
Typical attributes of a record:
Record or data structure name
Definition or description Alternate name(s) Attributes
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Data Dictionary Data Dictionary Reports
Many valuable reports may be obtained Data Element report Data Flows/Stores report Detailed reports
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Process Description Tools
A process description documents the details of a functional primitive
AND represents a specific set of processing steps and business logic
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Process Description Tools Modular Design
Based on the combination of 3 logical structures Sequence Selection Iteration - looping
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Process Description Tools
Typical process tools include: Structured English Decision Tables Decision Trees
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Process Description Tools Structured English
Purpose: Describe underlying business logic
Structured English Rules Use 3 building blocks
Sequence, Selection, Iteration Use indentation for readability Use limited vocabulary
Standard terms used in data dictionary Specific words that describe the processing rules
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Process Description Tools
Structured English (Pg. 174, Figure 4-37)
Might look familiar because it resembles pseudocode
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Process Description Tools Decision Tables
Decision Tables Logical structure All combinations of conditions Resulting actions
VERIFY ORDER Process
1. Conditions2. Combo of Y/N for condition – 4 diff. rules or combos3. X to accept or reject order given the rule
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3
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Process Description Tools Decision Tables
Decision Tables Can have > 3 possible outcomes Best way to describe complex set of conditions
Sales Promotion Policy
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Process Description Tools Decision Trees
Decision Trees Graph of conditions, actions, rules in decision table Personal preference Decision table or tree
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Logical Versus Physical Models Four-Model Approach
What analysts can do …
1st Create a physical model of current system
2nd Develop a logical model of current system
3rd Develop a logical model of new system
4th Develop a physical model of new system
Disadvantage: Added time and cost
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Chapter Summary
During data and process modeling, a systems analyst develops graphical models to show how the system transforms data into useful information
The end product of data and process modeling is a logical model that will support business operations and meet user needs
Data and process modeling involves three main tools: data flow diagrams, a data dictionary, and process descriptions
Data flow diagrams (DFDs) graphically show the movement and transformation of data in the information system
DFDs use four symbols
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Chapter Summary
A set of DFDs is like a pyramid with the context diagram at the top
The data dictionary is the central documentation tool for structured analysis
Each functional primitive process is documented using structured English, decision tables, and decision trees
Structured analysis tools can be used to develop a logical model during one systems analysis phase, and a physical model during the systems design phase
Any questions?