chap 2 - functional modeling

8/9/2019 Chap 2 - Functional Modeling

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Functional Modelling


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Objectives

To understand the modular design of system and to know about structureCharts .


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Scope

Process SpecificationControl Flow Model

Control SpecificationsStructure ChartsCohesion

Coupling CodingData Dictionary


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Process Specification

It is used to describe the details of theprocesses in the DFD of the system.

It contains the following input to the process the algorithm used performance characteristics relevant to process design constraints to implement the process


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Control Flow Model

Control flow modeling is required forapplications that are driven by events andproduce control information.For this, Control flow diagrams are madeThe CFD contain the same processes as the

DFD, but shows control rather than data flow


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Control Specification

It is used to indicate how the software behaves when an event or

control signal is sensed which processes are invoked as a consequence of

the occurrence of the event


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The control specification represents thebehaviors of the system in two ways:

It contains a State Transition diagram that issequential specification of behavior

It also contains a process activation table (PAT) -a combinatorial specification of behavior.


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Relationship between data and control models


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Structure ChartsModular programming - the complete systemis coded as small independent interactingmodules.Each module is aimed at doing one specifictask.The design for these modules is prepared in

the form of structure charts.Structure charts are developed prior to thewriting of program code


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Structure Charts

A structure chart is a design tool that pictorially shows the relation between processing

modules in computer software describes the hierarchy of components modules

and the data are transmitted between them


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Structure Charts - Notation

Program modules are identified by rectangleswith the module name written inside therectangle.Arrows indicate calls, which are anymechanism used to invoke a particularmodule.


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Structure Charts - Example

Mo dul e A

Mo dul e B Mo dul e M Mo dul e N

Mo dul e L

ZX

Y

Dat aPara meters

Control (fl ag)Infor mati on

Dat aPara meters

Control (fl ag)Inf ormati on

Di rect call t osubor di nat e module

Sel ecti on of subordi nat e modul edepends upon decisi on poi nt s or

iterati ve processing


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Cohesion

It is a measure of how tightly the statementsare related to each other in a module

Cohesion is the degree to which moduleserves a single purposeThere should be always high cohesion.


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CohesionFunctional Cohesion

A module performs just one function. This cohesion if present in modules does not

effect the overall performance of the system. But too much of it breaks modules down into

very small parts.

Sequential Cohesion Module consisting of those processing elements,which has the output of one as the input of thenext


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Cohesion

Communicational Cohesion Module consists of all processing elements, which

act upon the same input data set and/or producethe same output data set.

Procedural Cohesion Module formation associates processing elements

together since these are found in the sameprocedural unit.


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Cohesion

Temporal Cohesion module formation by putting together all those

functions, which happen at the same time.

Logical Cohesion module formation by putting together a class of

functions to be performed. It should be avoided.


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Cohesion

Coincidental cohesion This type of cohesion occurs when a module is

formed by taking the common code appearing inmore than one module.

That common code is taken out from modules andput into new module.

This type of cohesion should be avoided as itdoes not reflect the structure of problem.


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Coupling

Measure of interconnection among modulesin a program structure

Data coupling argument list data is passed to the module only data flows across modules


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Coupling

Control coupling Coupling where there is control flag - decision

control is in subordinate module

Common coupling Common coupling occurs when there are

common data areas - there are modules using datathat are global

It should be avoided


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CodingProgrammer codes each and every module of the system, giving a physical shape to thesystem.The programs should be written such thatthey are simple, easy to read, understand andmodify

Comment lines should be given to increasethe readability and modifiability of theprogram


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Data Dictionary

An organized listing of all data elements thatare pertinent to the system

Data dictionary contains the followinginformation: Name - the primary name of data or control item,

the data store, or an external entity. Alias - other names used for first entry


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Data DictionaryIt also tell about how that particular item isbeing used in the system.

For example, it will specify if it is process,

input,output, a data store, or an external entity.

l d l


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Summary

Structure charts are designing tools to show the relationship between the modules of the

system the hierarchy of modules data transmitted between these modules.

chap 2 - functional modeling

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