CMC ICT3207 Call Flow

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MIRZA REHENUMA TABASSUM

Using Data Flow Diagrams

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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}

(3)

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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Overview of Data and Process Modeling

Tools

• _{Systems analysts use many graphical}

techniques to describe an information system

• _{A data flow diagram (DFD) uses various}

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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 Diagrams

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Data Flow Diagrams

• _{DFD Symbols}

– _{Process symbol}

• _{Receives input data and produces output that has a}

different content, form, or both

• _{Contain the business logic, also called business rules} • _{Referred to as a black box}

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Data Flow Diagrams

• _{DFD Symbols}

– _{Data flow symbol}

• _{Represents one or}

more data items

• _{The symbol for a data}

flow is a line with a single or double arrowhead

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Data Flow Diagrams

• _{DFD Symbols}

– _{Data store symbol}

• _{Represent data that}

the system stores

• _{The physical}

characteristics of a data store are

unimportant because you are concerned only with a logical model

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Data Flow Diagrams

• _{DFD Symbols}

– _{Entity Symbol}

• _{Name of the entity}

appears inside the symbol

• _Terminators • _Source

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Creating a Set of DFDs

• _{Create a graphical model of the information}

system based on your fact-finding results

• _{First, you will review a set of guidelines for}

drawing DFDs. Then you will learn how to

apply these guidelines and create a set of

DFDs using a three-step process

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Creating a Set of DFDs

• _{Guidelines for Drawing DFDs}

– _{Draw the context diagram so that it fits on one}

page

– _{Use the name of the information system as the}

process name in the context diagram

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Creating a Set of DFDs

• _{Guidelines for Drawing DFDs}

– _{Do not cross lines}

– _{Provide a unique name and reference number for}

each process

– _{Obtain as much user input and feedback as}

possible

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Creating a Set of DFDs

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Creating a Set of DFDs

• _{Step 2: Draw a Diagram 0 DFD}

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Creating a Set of DFDs

• _{Step 2: Draw a Diagram 0 DFD}

– _{If same data flows in both directions, you can use}

a double-headed arrow

– _{Diagram 0 is an exploded view of process 0}

– _{Parent diagram}

– _{Child diagram}

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Creating a Set of DFDs

• _{Step 3: Draw the}

Lower-Level Diagrams

– _{Must use leveling and}

balancing techniques

– _{Leveling examples}

• _{Uses a series of}

increasingly detailed DFDs to describe an

information system

• _{Exploding, partitioning, or}

decomposing

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Creating a Set of DFDs

• _{Step 3: Draw the}

Lower-Level Diagrams

– _{Balancing Examples}

• Ensures that the input and output data flows of the parent DFD are

(19)

Data Dictionary

• _{A data dictionary, or data repository, is a central}

storehouse of information about the system’s

data

• _{An analyst uses the data dictionary to collect,}

document, and organize specific facts about the

system

• _{Also defines and describes all data elements}

and meaningful combinations of data elements

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Data Dictionary

• _{A data element, also called a data item or}

field, is the smallest piece of data that has

meaning

• _{Data elements are combined into records, also}

called data structures

• _{A record is a meaningful combination of}

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Data Dictionary

• _{Using CASE Tools for Documentation}

– _{The more complex the system, the more difficult it}

is to maintain full and accurate documentation

– _{Modern CASE tools simplify the task}

– _{A CASE repository ensures data consistency}

– _{You will learn more about CASE tools in Part 2 of}

the Systems Analyst’s Toolkit

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Data Dictionary

• _{Documenting the Data}

Elements

– _{You must document}

every data element in the data dictionary

– _{The objective is the}

same: to provide clear, comprehensive

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Data Dictionary

• _{Documenting the Data Elements}

– _{The following attributes usually are recorded and}

described

• _{Data element name and 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 usually are recorded and}

described

• _Source • _Security

• _{Responsible user(s)}

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Data Dictionary

• _{Documenting the Data Flows}

– _{The typical attributes are as follows}

• _{Data flow name or label} • _Description

• _{Alternate name(s)} • _Origin

• _Destination • _Record

• _{Volume and frequency}

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Data Dictionary

• _{Documenting the Data Stores}

– _{Typical characteristics of a data store are}

• _{Data store name or label} • _Description

• _{Alternate name(s)} • _Attributes

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Data Dictionary

• _{Documenting the Processes}

– _{Typical characteristics of a process}

• _{Process name or label} • _Description

• _{Process number} • _{Process description}

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Data Dictionary

• _{Documenting the Entities}

– _{Typical characteristics of an entity include}

• _{Entity name} • _Description

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Data Dictionary

• _{Documenting the Records}

– _{Typical characteristics of a record include}

• _{Record or data structure name} • _{Definition or description}

• _{Alternate name(s)} • _Attributes

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Data Dictionary

• _{Data Dictionary Reports}

– _{Many valuable reports}

• _{An alphabetized list of all data elements by name}

• _{A report describing each data element and indicating the}

user or department that is responsible for data entry, updating, or deletion

• _{A report of all data flows and data stores that use a}

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Process Description Tools

• _{A process description documents the details of}

a functional primitive, which represents a

specific set of processing steps and business

logic

• _{It should be noted that this chapter deals with}

structured analysis, but the process

description tools also can be used in

object-oriented development, which is described in

Chapter 6

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Process Description Tools

• _{Modular Design}

– _{Based on combinations of three logical structures,}

sometimes called control structures, which serve as building blocks for the process

• _Sequence • _Selection

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Process Description Tools

• _{Structured English}

– _{Must conform to the following rules}

• _{Use only the three building blocks of sequence,}

selection, and iteration

• _{Use indentation for readability}

• _{Use a limited vocabulary, including standard terms used}

in the data dictionary and specific words that describe the processing rules

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Process Description Tools

• _{Structured English}

– _{Might look familiar to programming students}

because it resembles pseudocode

– _{The primary purpose of structured English is to}

(35)

Process Description Tools

• _{Decision Tables}

– _{Shows a logical structure, with all possible}

combinations of conditions and resulting actions

– _{It is important to consider every possible outcome}

to ensure that you have overlooked nothing

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Process Description Tools

• _{Decision Tables}

– _{The number of rules doubles each time you add a}

condition

– _{Can have more than two possible outcomes}

– _{Often are the best way to describe a complex set}

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Process Description Tools

• _{Decision Trees}

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Logical Versus Physical Models

• _{While structured analysis tools are used to}

develop a logical model for a new information

system, such tools also can be used to develop

physical models of an information system

• _{A physical model shows how the system’s}

(39)

Logical Versus Physical Models

• _{Sequence of Models}

– _{Many systems analysts create a physical model of}

the current system and then develop a logical model of the current system before tackling a logical model of the new system

– _{Performing that extra step allows them to}

understand the current system better

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Logical Versus Physical Models

• _{Four-Model Approach}

– _{Develop a physical model of the current system, a}

logical model of the current system, a logical

model of the new system, and a physical model of the new system

– _{The only disadvantage of the four-model approach}

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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