From Flow Charts to UML 2

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From Flow Charts to UML - 2
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Agenda

• Decision Tables
• Logic Flowcharts
• Structured English
• Data Flow Diagrams

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Decision Tables

• A way of thinking through processes which have
  already been decomposed
• Example Insurance Claim Decision

Pay out x - - - Refusal - Letter A -
x - - Refusal - Letter B - - x
- Refusal - Letter C - - - x
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Decision Tables

• Advantages
• Every combination of conditions is tested
• There are 2n ways in which the conditions can be
  combined
• Where n number of conditions
• Each outcome is predicted before the system is
  tested

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Decision Tables

• Advantages
• A clear tabular representation linking conditions
  with actions
• Ensure an exhaustive coverage of all possible
  cases
• Can show up redundancy and inconsistency in a set
  of rules
• Easy to follow in operation
• Can be incorporated into program specifications

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Decision Tables

• Disadvantages
• Can become very unwieldy
• Only suitable where there is little interleaving
  between the evaluation of conditions and
  execution of actions

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Logic Flowcharts

• In a complex decision making process, Decision
  Tables may have to be linked to many subsidiary
  Decision Tables
• Logic Flowcharts are designed to address this
  problem
• Flows do NOT represent data or documents
• Flows represent the control of the process

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Logic Flowcharts

• Example Insurance Claim Decision

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Logic Flowcharts

• Advantages
• Easy to understand and follow
• Can be used in procedures manuals to follow a
  task
• Good at representing cases where there is an
  interleaving of actions and evaluations
• Can be used to specify programs

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Logic Flowcharts

• Disadvantages
• Encourage the use of GOTO statements in
  programming. Can lead to logic which is difficult
  to unravel
• Difficult and time - consuming to alter

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Structured English

• Process logic is described using 3 structures
• A sequential block of statements
• Decision structures,
• the 2-way decision IF, THEN, ELSE
• the multi-way decision CASE, CASE 1, CASE 2, CASE
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• Repetition structures
• DO WHILE
• REPEAT, UNTIL

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Structured English

• Example Insurance Claim Decision
• fetch CLAIM
• fetch GARAGE_REPORT
• fetch POLICY_TYPE
• fetch POLICY_EXCESS
• CASE POLICY_TYPE, POLICY_EXCESS
• CASE 1 POLICY_TYPECOMP, POLICY_EXCESSltCLAIM
• pay out
• CASE 2 POLICY_TYPE3rdPFT, POLICY_EXCESSgtCLAIM
• send refusal letter A

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Data Flow Diagrams (DFDs)

• Identify the major processes
• Identify the major sources, sinks and stores
• Identify the major data flows
• Name the flows, processes, sources, sinks and
  stores
• Draw the diagram
• Review the diagram, checking for logical
  consistency

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Data Flow Diagrams (DFDs)

• Focus on the logical model of the system
• Start with overview - Context diagram, or Level 0
• Concerned with
• what happens,
• not how or where it happens
• Top down, then decompose

Motor Insurance Claim
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Data Flow Diagrams (DFDs)

• Decomposition - Level 1

Verification
Data entry
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Data Flow Diagrams (DFDs)

• An important tool of structured analysis and
  design.
• Makes no commitment to physical design of the
  system.
• Data stores may become part of a database, and
  processes may become programs
• A DFD is readable by non-technical staff
• may therefore become part of the agreed
  Requirements Specification

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End of Lecture