STRUCTURE CHART CREATION

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STRUCTURE CHART CREATION

• USE THE DATA FLOW DIAGRAM (DFD) TO IDENTIFY THE
  MAIN/CENTRAL MODULES
• TRANSFORM/TRANSACTION CENTRES
• REARRANGE THESE MODULES, IF NECESSARY, IN A
  HIERARCHY PLUS INPUT-PROCESS-OUTPUT (HIPO)
  SEQUENCE
• REPLACE DFD NOTATION WITH STRUCTURE CHART NOTATION

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REFINE THE STRUCTURE CHART

• PROVIDE ADDITIONAL PROCESSING DETAIL
• KEEP IN MIND PROGRAM DESIGN CRITERIA
• ADD DATA AND CONTROL INFORMATION AS IS NECESSARY

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CRITERIA FOR GOOD PROGRAM DESIGN

• Objectives
• ERROR-FREE OPERATION
• MAINTAINABILITY
• EFFICIENCY (EASY TO READ AND CODE)

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Properties

• MODULARITY (i.e. HIERARCHICAL ORGANIZATION OF
  MODERATELY SIZED MODULES)
• MODULE REUSABILITY (i.e., MODULE SHOULD BE
  GENERIC)
• MODULE CLARITY (i.e., EACH MODULE PERFORMS ONE
  FUNCTION)

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GOOD PROGRAM DESIGN -

• DETERMINING MODULE BOUNDARIES
• HIGH COHESION
• MODERATE SPAN OF CONTROL
• LOW COUPLING

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Coupling and Cohesion

• COHESION FOCUSES ON WHAT'S INSIDE A MODULE, I.E.,
  THE GLUE" HOLDING THE MODULE TOGETHER
• GENERALLY, THE MORE PURPOSES A MODULE SERVES, THE
  LOWER THE COHESION AND THE POORER THE DESIGN

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Coupling and Cohesion (2)

• COUPLING FOCUSES ON THE CONNECTIONS BETWEEN
  MODULES IT HIGHLIGHTS MODULE INTER-RELATEDNESS
• THE GREATER THE INTERDEPENDENCE BETWEEN MODULES,
  THE HIGHER THE COUPLING AND THE POORER THE DESIGN

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COHESION

• (BEST TO WORST RANKING)
• FUNCTIONAL COHESION
• Module carries out a single task

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SEQUENTIAL COHESION

• Tasks are placed in the same module because
  they must be executed in sequence
• i.e., they require each other's input or output

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COMMUNICATIONAL COHESION

• Subtasks use the same data but are not
  otherwise related,
• e.g., a module that computes the patient's bill
  and generates a government report

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PROCEDURAL COHESION

• Subtasks happen to occur one after the other,
• e.g., calculating the average doctor's salary and
  calculating the average number of hours worked
  per week by nurses

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TEMPORAL COHESION

• Tasks have to be performed at the same
  time,
• e.g., putting all initialization routines in one
  module

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LOGICAL COHESION

• Functions are logically similar but
  procedurally different,
• e.g., reporting doctor information and staff
  information

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COINCIDENTAL COHESION

• No clear reason for having the functions in the
  same module

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COUPLING

• (BEST TO WORST RANKING)
• DATA COUPLING
• Only data are passed between modules through
  explicit calling parameters

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STAMP COUPLING

• Data are passed in the form of data structures
  or entire records

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CONTROL COUPLING

• Control flags are sent from calling modules to
  called modules calling modules know something of
  the internal structure of called modules

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COMMON COUPLING

• Modules share data in a global area

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CONTENT COUPLING

• One module is able to modify the content or
  function of another module

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DOCUMENTATION

• STRUCTURE CHARTS CANNOT STAND ALONE AS SOLE
  PROGRAM DOCUMENTATION TECHNIQUE
• I. DATA FLOW DIAGRAMS GIVE BIG PICTURE SHOW
  INTERCONNECTIONS BETWEEN MODULES
• II. STRUCTURE CHARTS GIVE PICTURE OF HIERARCHY
  PLUS INPUT/PROCESS/OUTPUT BETWEEN AND WITHIN
  MODULES

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REPRESENT

• SEQUENCE
• CONDITIONAL STATEMENTS
• ITERATION
• PSEUDOCODE, LOGIC MODELS ETC. GIVE MORE DETAIL IF
  NECESSARY