systems analysis & design (sixth edition) 1 chapter 4 data and process modeling phase 2: systems...

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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?