Representational & Software Tools in SDD

Software Design and Development

Contents

2. Data flow diagram2. Data flow diagram

1. Context diagrams1. Context diagrams

3. Data Dictionary3. Data Dictionary

4. IPO Chart4. IPO Chart

5. Storyboard5. Storyboard

6. Structure Chart 6. Structure Chart

7. System flowcharts7. System flowcharts

Course Specifications

8. CASE tools8. CASE tools

NSW BOS Course Specifications

Context Diagram

TEXT TEXT TEXT

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process

External Entity

Context diagrams are used to represent entire information systems.

The system is shown as • a single process along with • the inputs and outputs (external entities) to the system.• the external entities are connected to the single process by data flow arrows.

The symbols used are:

Processa single process representing the entire system as a circle

Data Flowdata flow representing the flow of data between the single process and external entities

External Entityany person or organisation that provides data to the system or receives data from the system, represented by a box

Data Flow Diagram

A data flow diagram provides more detail at a lower level for a context diagram.

Data flow diagrams represent the information system as a number of processes that together form the single process of a context diagram.

The source of data, its flow between processes and its destination along with data generated by the system is represented.

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Data Flow Diagramsymbols used

ProcessCircles used to represent processes. Processes are actions taking place to transform inputs to outputs.

Data FlowCurved lines represent data flows between processes, data stores and external entities. Data flows should be named to identify the piece of data.

External EntityBoxes used to represent external entities. These are any item, person or organisation sitting outside the systems that provides data to the system or receives data from the system.

Data StoreAn open-ended rectangle is used to represent a data store. It is a location where data is stored. It can be in computer format, such as a diskette, or in non-computer format, such as a filing cabinet or an answering machine.

process

External Entity

Data Store

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Data Flow Diagramexample

The example below shows the processes involved in borrowing a video.

                                                                                           The example below shows the processes involved in borrowing a video.

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Data dictionaryexamples

A data dictionary is a table providing a comprehensive description of each field in the database.

• This commonly includes: • field name• data type, • data format

(incl.. no. of decimal places,if applicable)

• field size (i.e. no. of characters or field width)

• Description• example.

• This is shown in the example on the right.

                                                                                                                                                                                                        Field name Data type Data format Field size Description Example

UserId Text NNNNNNNN 8Unique eight-digit number represented as text

0001539

FirstName Text   25 First name of employee Bill

Surname Text   25 Surname of employee Smith

DOB Date DD/MM/YYYY 10Date of birth as a short date format

15/07/1982

HourlyPayRate Currency #####.## 8Rate of pay expressed in dollars per hour

34.50

Height Real #.## 3Height in metres, with two decimal places

1.58

FeesPaid Boolean   1 Y or N for Yes or No Y

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IPO Chart

A decision tree is a diagrammatic way of representing all possible combinations of decisions and their resulting actions. Branches are shown to describe the eventual action depending on the condition at the time. Each decision path will lead to either another decision that needs to be made or a final action. This is shown in the example below.

                                                                                          

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These charts are used to document • the inputs into a process, • the general nature of the processes performed on this input,

and• outputs produced for each task or process in a system.

When used in conjunction with a structure chart, one IPO chartshould be produced for each lowest level process on thestructure chart.

The IPO chart is in the form of a table with 3 columns: 1. Input2. Process3. Output.

IPO Chartexamples

A decision tree is a diagrammatic way of representing all possible combinations of decisions and their resulting actions. Branches are shown to describe the eventual action depending on the condition at the time. Each decision path will lead to either another decision that needs to be made or a final action. This is shown in the example below.

                                                                                          

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The IPO chart is in the form of a table with 3 columns, one for each of Input, Process and Output.

Validation of student information:

Input Process Output

Student id(read from magnetic card)

Read student record

Valid-student-flag

Password(read from keyboard)

Compare entered password

Check if correct

0 if correct1 if incorrect

Student id

The same information can be expressed in a different format, as follows:System School Library System

Process Name: Validate student information

Input: Student id(read from magnetic card)

Password(read from keyboard)

Process: Read student record

Compare entered password

Check if correct

Output: Valid Student Flag (0 if valid, 1 if invalid)

Storyboards

• Screens should contain sufficient detail to indicate the general layout of• Text• Fields• Graphics• Buttons

• The flow between screens is indicated by the use of arrows.

• Where a button click causes the movement to the next screen, the arrow should start from the appropriate button.

The storyboard example shows the relationship between three pages of information aimed at promoting a school canteen on a website.

Elements of each screen are clearly identified and the links between screens shown.

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Storyboards are used to document the screens used in a system,and the flow between them.

Structure Chart

Structure diagrams allow the representation of a system broken down into its separate

• subtasks or • processes.

The relationship between each of these processes should also be evident from the diagram.

Rectangles are used to represent tasks, with lines used to showthe connections between tasks.

The chart is read from:• top to bottom, with component subtasks on successively lower levels,

and from• left to right to show the order of execution of tasks at the same level.

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Structure Chartsymbols used

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The symbols used in Structure Charts are:

Data movement between tasks (usually passed as parameters) is shown with the use of arrows.

A filled circle is used to indicate a flag.

A decision (ie optional execution of a task) is indicated by useof a small diamond at the intersection of the line.

Repetition (execution of a particular task multiple times) isshown by a circular arrow.

Structure Chartexample

Contents

The following example illustrates the features of a Structure Chart:

System Flowcharts

                                                                                                                                                                                                        

                                                                                                                                                                                                        

Data dictionary

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System flowcharts are a diagrammatic way of representing both the • flow of data and• logic

through an information system.

They were once the primary tool for documenting systems; however, data flow diagrams are often used instead.

1. Standard flowcharting symbols are used along with 2. Symbols for representing physical devices that

• Capture data• Store data• Display data.

N.B. Many of these symbols have become out of date as a result of changes in technology.

System Flowchartssymbols used

                                                                                                                                                                                                        

                                                                                                                                                                                                        

Data dictionary

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Symbols used in System Flowcharts

CASE Tools

CASE tools software must allow the production and maintenance of:• Manuals, incorporating

• screen shots• table of contents• index

• Flowcharts• Gantt charts• Data dictionary• System flowcharts• Modelling tools such as:

• Structure charts• Data flow diagrams • Other appropriate modelling tools.

Recommended software:• Word processing• Spreadsheet • Drawing packages with appropriate graphics items.• CASE Tools such as

• Ascent• together-J• Rational Rose.

Gantt Chart

Gantt charts display the overall timeline for a project.

They present a sequential breakdown of individual tasks showing the relationship between tasks and the time taken for each task.

The duration of tasks are shown as horizontal bars.

Gantt charts should have labelled axes:• Y-axis for tasks and• X-axis for time.

A time scale should be shown, including dates.

Milestones should also be included.

Gantt Chartexample

The example below shows the main elements of a Gantt chart.