SeminarI Version1.1

7/30/2019 SeminarI Version1.1

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System Analysis

Environmental ModellingDevraj MandalMaster of Control System Engineering

J adavpur University


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Outline

Classical Modelling Approach

The Essential Model

Components of the Essential Model

Environmental Model

System Boundary

Statement of Purpose

Context Diagram

Event ListAdditional Components

Behavioural Model

Reference


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Classical Modelling Approach

Model of the actual system that the

user is currently using.

Current

Physical Model

Is a model of the pure or essentialrequirements being carried out by the

users current system.

Current Logical

Model

Is a model of the pure or essentialrequirements of the new system that

the user wants.

New LogicalModel

Model showing the implementationconstraints imposed by the user.New Physical

Model


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New Logical Model Ideally same as the current logical model.

May contain same functions and the same data butits implementation has to be changed.

Hardwareobsolete

Poor SystemPerformance

Manual workto be

automated

Add newfunctions

Lack of properdocumentation


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3 assumptions

Currentlogicalmodel

Addeddata

/functions

NewLogicalModel

Computer Expertworking in banking.Unfamiliarity

with projectarea

A type of prototypedeveloped.Lack of

experience


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Essential Model

Model of what the system must do to satisfy userrequirements.

No knowledge about System Implementation

Specific implementation only in design phase.


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Components of the EssentialModel

Statement of Purpose Context Diagram Event List

Environmental Model

Data Flow Diagram Entity-Relationship diagrams

State-transition diagrams Data Dict ionary Process Specifications

Behavioural Model

f h i l


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Components of the EssentialModel

Statement of Purpose Context Diagram Event List

Environmental Model

Data Flow Diagram Entity-Relationship diagrams

State-transition diagrams Data Dict ionary Process Specifications

Behavioural Model


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Environmental Model

What are inside & outside of the system?

System Boundary

How does the system communicate with theoutside?

Interface

Events that only occur outside the system. System must generate a response for that input.

Inputs/Outputs


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System Boundary (Scope)

Unsatisfied Requirement & Functionalities.

Small scope

Development becomes complex. Time-consuming & costly.

Large scope

Everything inside system boundary.

Domain of Change


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System Boundary

The area inside the system boundary is called

the domain of change


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Health-care Appointment System

User of

System

Software

&

Hardware


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Statement of Purpose

Top Management User Management Others not involved in its development

A brief concise textual statement of the

purpose of the system.

The purpose of the Book Processing System is tohandle all of the details of customer orders forbooks, as well as shipping, invoicing, and back-billing of customers with overdue invoices.

Book Processing System


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Context Diagram

A special case of a dataflow diagram (DFD) in

which a single bubble represents the entiresystem.

Externalentities

Input tosystem

OutputDatastores

SystemBoundary


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Context Diagram

i


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Event List

Thesystem

TemperatureSensor

Too cold

The system

TemperatureSensor

MonitorTemperature

Too cold

Temperature Arrives

Stimuli must occur in the environment. Systems response to it should be positive. Timing of the events occurrence must be noted.

A list of stimuli that acts on the system


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Types of Events

A piece of data arrival, signals an event.All data flows are not events.

Flow oriented event (F)

Events triggered by the arrival of a point of t ime.

Temporal event (T)

An unpredictable Temporal data flow No data is associated with this flow.

Control event (C)

E Li C i


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Event List Construction

Input Response

F A book is acquired. Update catalogue

F A member borrows a book Update book status

Update members on-loan status

F A member returns the book Update book status

Update members on-loan status

F A member renews the loan of a

book

Update book return date

F A member asks for a already

borrowed book

Update book status

Update waiting listT A loan period expires Overdue not ice

Update member status

Administration department asks

for overdue list & waiting list.

Send Overdue List & Waiting List


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Additional Components

Organised listing of all the data elements thatare pertinent to the system.

Precise , rigorous definitions of allinputs/outputs, stores & intermediate

calculations.

Initial Data Dictionary

Database Administration Not a functional model Nor a time-dependent model

Entity-Relationship model


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Behavioural Model

Describes the required behaviour ofthe insides of the system necessary tointeract successfully with the

environment.


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Reference

S.Goldsmith,A Practical Guide to Real TimeSystems Development, Prentice Hall, 1993.

E.Yourdon. (1989). Just Enough Structured

Analysis [Online]. Available:http://www.yourdon.com/strucanalysis/wiki/index.php/Introduction


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Backup Slides


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Implementation details in Essential Model

To show flow between processes.

Sequencing

As processes work at different rate & time.

Scheduling

For the sake of efficiency & robustness.

Redundant & derived data

As we work with error-prone systems.

Error-Checking & Validation


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Basic Notations of DFDA producer or a consumer of

Information that resides outside thebounds of the system to be modelled.

A transformer of information (afunction) that resides within thebounds of the system to be modelled.

A data object ; the arrowheadindicates the direction of data flow.

A repository of data that is to be storedfor use by one or more processes ;may be as simple as buffer or queueor as sophisticated as a relationaldatabase

Externalentity

process

Store

B i N i f DFD


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Basic Notations of DFD

TerminatorA producer

or consumerof

information

outside thesystem

Functionor Process

Data Flow

DataStorage

Buffer Queue

Database

Notation extension for RTS


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Notation extension for RTSA data object that is input or outputfrom a process on a continuousbasis

A transformer of control or events;accepts control as input and producescontrol as output.

A control item or event; takes on aBoolean or discrete value ; thearrowhead indicates the direction ofthe flow

A repository of control items that are tobe stored for used by one or more

process.

Multiple equivalent instances of thesame process; used for multitaskingsystem.

Controlprocess

Control store

Control item

Continuousdata flow

process

N t ti f R l Ti S t


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Notation for Real Time Systems

Control

Process

ControlStore

Controlflow

Multipleinstances


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Context Diagram Construction

Typically the name of the System.

Single bubble

Cannot communicate directly with each other. More convenient to draw terminators more than

once.

Show source of data instead of handlers

Indicate the role of person instead of hisidentity

Terminators


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customer order is received by the system customer places order

Events and event-related flow.

Not from Systems but from environmentsviewpoint.

Describe the event.

Any variations of this event ?Are the opposite/negative of this events of

interest ?Are there any events that must precede/follow

this events ?

What if the events fail ? (failure-mode approach)

Checklist

Data Dictionary


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Data Dictionary

Name Aliases Definition

General

Data type Length Units Picture

Format

Range of values Frequency of use Input/output/local Conditional values Limits

Usage Characteristics

Parent Child Data Flow File

Relationships

Documents

SeminarI Version1.1