8. PROCESS 8. PROCESS

DESCRIPTIONDESCRIPTION

System Analysis And Design

Program: BSCS II (Advent Semester – 2014)

Lecturer: Rebecca Asiimwe

Email: rasiimwe@technology.ucu.ac.ug1

Process Description-Logic Modeling

• Data flow diagrams do not show the logic inside the processes

• In our previous lecture, we noted processes such as Verify Order, Compute Marks, Validate Application, but we did not explain the logic necessary to execute these tasks. The methods available for documenting and analyzing the logic of decisions include structured English, decision tables, and decision trees.

• Logic modeling can also be used to show when processes on a DFD occur.

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Goals of Process Description

1. To reduce the ambiguity of the process. This goal compels the analyst to learn details about how the process works. Any vague areas should be noted, written down, and consolidated for all process specifications. These observations form a basis and provide the questions for follow-up interviews with the user community.

2. 2. To obtain a precise description of what is accomplished.

3. To validate the system design. This goal includes ensuring that a process has all the input data flow necessary for producing the output. In addition, all input and output must be represented on the data flow diagram.

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Goals of Process Description

• Note: you will find many situations in which process specifications are not created/required.

• Sometimes the process is very straight forward and simple. A process such as “Receive Applications” may not need further description while a process such as “Choose Winner” may prompt an analyst to further probe this process for details - how is a winner chosen (what conditions are looked at)?

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Process Description

–Process Description may be achieved using;

• Structured English• Decision tables• Decision Trees

– These are the commonly used techniques

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Structured English

• It is a way of describing the flow of a process

• Structured English is a modified form of English used to specify the logic of information processes.

• Used when the process logic involves formulas or iterations, or when structured decisions are not complex.

• A process will follow sequentially but at times a selection needs to be made or a repetition condition is required.– Uses Instructions, repetitions and if-then-else logic– Note that this is not necessarily a computer program (its an

algorithm that describes the process)

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From user-speak to programming

User

Structured English

Analyst

Programs

Programmer

Plain English

Pseudo code

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Modeling Logic with Structured English

• Uses a subset of English

–Action verbs–Noun phrases– It should read like English

• No specific standards exist9

Structured English

• Well suited for many process descriptions• A series of informal English statements• Uses a small selected vocabulary• Provides effective communication between

users and programmers• Users are generally more comfortable with

these English statements• Sufficiently precise to avoid misinterpretation

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Structured English - Style

• Keep statements brief

• Use and capitalize accepted keywords such as IF, THEN, ELSE, DO, DO WHILE, DO UNTIL, and PERFORM.

• Use small group of words –avoid being verbose

• Indent blocks of statements to show their hierarchy (nesting) clearly.

• Use strong, action- oriented verb with an object e.g. compute, print, copy, update, validate

• Structured English should NOT be as rigorous as a programming language.

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Example

Process: Check Patient Status

Process DescriptionIF Patient is a new patientTHEN Perform Add new patient ProcessELSE

IF patient has unpaid billsTHEN transfer the patient to the business office

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• Represent the logic in this table as Structured English

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Structure English Representation

IF employee type is Salary

THEN pay base salary

ELSE

IF employee type is Hourly AND works for <40 hours

THEN calculate hourly wage and absence Report

ENDIF

IF employee type is Hourly AND works for 40 hours

THEN calculate hourly wage

ENDIF

IF……

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Limitation of Structured English

– Not so good for showing complex decision logic

– Not so good if there are few or no sequential steps

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Decision Trees

• A decision tree is a graphical description of process logic that uses lines organized like branches of a tree.

• They are helpful where there is a large number of nested IF statements

• Decision Trees use a circle to represent a condition point and a square node to indicate an action (outcome branches like branches of a trees )

• Using notation makes the decision tree more readable, as does numbering the circles and squares sequentially. Think of a circle as signifying IF, whereas the square means THEN.

• Easy to construct and understand

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• Illustration of Decision Tree

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Decision Tree Diagram

Constructing a Decision Tree

• Identify all decision variables, and the possible values for each variable

• Generate the tree systematically (left to right)– Draw one branch from the root for each value of the

first decision variable- label each branch

– The right end of each branch is a decision point

– At each decision point, draw one branch for each value of the next decision variable - label each branch

– Repeat until no more decisions.19

Constructing a Decision Tree (Cont)

• Identify the independent actions, and label

each leaf with the action (s) to be taken

• Formulate questions for users to resolve

omissions and ambiguities etc.

• Revise and complete the decision tree.

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Example

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Decision Tree Example

A point-of-sale example was used to determine the purchase approval actions for a department store.

Conditions included the amount of the sale (under $50) and whether the customer paid by check or credit card.

The four actions possible were to ring up the sale, look up the credit card in a book, call the supervisor for approval, or call the bank for credit card authorization.

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Decision Tree Example

Decision Table

• Is a matrix representation of the logic of a decision.• Specifies the possible conditions and the resulting

actions• It’s best used for complicated decision logic• Show a logical structure that describe a process logic• Every logical combination is shown initially• Results then can be combined and simplified• Programmers can use decision tables in developing

code

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Decision Tables (Cont)

• Consists of three major parts:• Condition stubs-lists conditions relevant to

decision. Describes the conditions or factors that will affect the decision

• Action stubs- lists actions that result from a given set of conditions. Describe the possible policy actions or decisions

• Rules- specify which actions are to be taken for a given set of conditions

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Decision Tables

• A decision table is a table of rows and columns, separated by four quadrants.

• Programmers can use decision tables in developing code

CONDITIONS AND ACTIONS

RULES

Conditions Conditions alternatives

Actions Action entries

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Decision Table Diagram

Condition

List (statement)

Condition

Matrix (entries)

Action

List (statements)

Action

Matrix (entries)

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Decision Table for Payroll System Example

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Steps to Construct a Decision Table

1. Identify conditions & values2. Compute maximum number of Rules3. Identify possible actions4. Enter all Possible Rules5. Define Actions for each rule6. Verify the policy7. Simplify the table

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Example- Refer to appended notes

• Scenario: A marketing company wishes to construct a decision table to decide how to treat clients according to three characteristics: Gender (M or F), City resident (Y or N), and age group: A (under 30), B (between 30 and 60), C (over 60).

• The company has four products (W, X, Y and Z) to test in the market. Product W will appeal to female city residents. Product X will appeal to young females (under 30). Product Y will appeal to Male middle aged shoppers who do not live in cities. Product Z will appeal to all but not to older females.

Interpret this Decision Table

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Decision Tables

• Advantages of Decision Tables

– It’s concise, unambiguous, clearly conveying the logic involved, hence less danger of omitting a logical possibility

– Enhanced communication with action separated from conditions

– Easier to draw and they’re easily understood.

– Produces an automatic compact program documentation.

– Its’ format is highly standardized

– Can be checked mathematically for completeness and that all test combinations have been considered.

• Disadvantages of Decision Tables

– However they do not show the sequence of decisions 32

Decision Table or Decision Tree?

• Major advantages of Decision Table is the guaranteed consideration of ALL combinations of conditions and their resultant actions.

• Most users prefer the graphic nature of a decision tree.

• Which of the two should be used?33

Guidelines for using a Decision Table or a Decision Tree

• Use a Decision Table when there are many decision variables

• Use a Decision Table when decision rules require combination of actions

• Use a Decision Tree when there are few decision variables and only one action per rule.

• Use a Decision Table as a working tool when need to check all combinations of conditions– Present the policy as a decision tree, if it

satisfies the above.34

More:1. Use structured English when

a. There are many repetitious actions, OR

b. Communication to end users is important.

2. Use decision tables when

a. Complex combinations of conditions, actions, and rules are found, OR

b. You require a method that effectively avoids impossible situations, redundancies, and contradictions.

3. Use decision trees when

a. The sequence of conditions and actions is critical, OR

b. When not every condition is relevant to every action (the branches are different). 35

Q & A

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