unit 13 university of sunderland comm1b information systems analysis 1 identifying system...

1Unit 13University of Sunderland COMM1B Information Systems Analysis

Identifying system improvements: Logicalisation

Information System AnalysisCOMM1B

Unit 13


Identifying Potential System Improvements

Examining an existing system can lead to the identification of the potential for improved processing activity.

This often results in: Construction of a modified model to support this change.


Identifying possible system improvements

• Problems lead to requirements – (See Unit 14)

• Requirements Catalogue

• Operational and Strategic Objectives may bring about change – Covered in COMM1F

• Business Process Re-engineering (BPR)• Process Improvement for Strategic Objectives

(PISO)

• Start with logicalisation of current system


• Why model the current system?– Develop an understanding and feel for the

information system– Systems adapt and evolve over a period of

time• Often results in a system which does not fully

reflect what the system was intended to do

– The old system may need to be changed or even replaced to accommodate new business requirements

System Modelling


• Current Physical Model– Describes how the present system is

implemented

• Current Logical Model– Reflects the policy behind the system

• without the physical circumstances and constraints of the existing system

• forces the analyst to think logically and abstractly• forms the basis for the specification of the required

system

Current System Model


Current PHYSICAL System Model

Current LOGICAL System ModelAdd New System Requirements, Consider Business System Options

Required LOGICAL System Model

Required PHYSICAL System Specification

Stages of Systems Analysis and Design

Investigate and analyse system

Add Implementation Details, Consider Technical System Options

Perform Logicalisation


Logicalisation• The beginning of the ‘transformation’ of the old

system to the new system– Mainly involves reconstructing the set of levelled

DFDs• Physical DFDs show

– What is done, – Where and – How it is done, – Who does it

• Logical DFDs only show – What is done

– Refined entity model after normalisation


Simple Example of Physical level 1 DFD

Discuss party details and record interest

1 You

Invite guest by telephone

2 You

Produce and send out tickets to party

3 You

M1

M3

M2

Address Book

Phone directory

Diary

Colleague

M1 Diary

Party details

Person details

Party enquiry

Party details

Party invitation

Ticketsresponse

*


Logicalised level 1 DFD

Communicate and record party data

1

Colleague

D1 Party Data

D2 Contact Data

Party details

contact details

Party/contact data


Example

• The following example of a student assessment system is used to illustrate the technique of logicalisation– taken directly from Lejk and Deeks, chapter 9


Set andMark

Assessments

Subj Tutor1

*

Collatemarks for

all students

Yr leader2

*

Moderateand finalize

results

BoE3

Producepasslist

Sch Admin4

Course documentM1

Timetabler

Examsoffice

Examsoffice

Student

Headof

School

Regulations

Regulations

Coursework &exam marks

Student marks &mitigating evidence

Finalisedresults

Timetable

Completedexamination

Examinationpaper

AssignmentCompletedassignment

Markedassignment

Mitigatingevidence

Results

Stamped addres-sed envelope

Pass list andresults

Pass list

Signed passlist

Level 1 Current Physical DFD


Set and Mark Assessments1

*

Collatemarks for

all students

Yr leader2

Examsoffice

Student

Timetabler

Student

*

Prepareassessments

Subj Tutor1.1

*

Receiveand mark

assessments

Subj Tutor1.2

*

Calculateend ofyear

marks

Subj Tutor1.3

Subject resultsfileD1/1


Examinationpaper

Assignment

Timetable

Completedassignment

Completedexam paper

Markedassignment

Assignment &exam marks

Assignment &exam marks




Collate marks for all students2

*


results

BoE3

Course documentM1

Set andMark

Assessments

Subj Tutor1

Student

*

Enter marksinto

spreadsheet

Yr leader2.1

*

File mitigatingevidence

Yr leader2.2

*

Preparefor Board

of Examiners

Yr leader2.3

Spreadsheetmarks fileD2/1

Mitigating evidencefileM2/2

Spreadsheetmarks fileD2/1


Regulations


Mitigatingevidence

Marks

Evidence

Evidence

Marks



Produce pass list4

Examsoffice

*


results

BoE3

Headof

School

Student

Producepasslist

Sch Admin4.1

*

Filepasslist

Sch Admin4.2

*

Match resultsto envelopes

Sch Admin4.3

*

Set upenvelope

file

Sch Admin4.4

*

Send resultsto exams

office

Sch Admin4.5

Course resultsfileM4/1

Course resultsfileM4/1

EnvelopefileM4/2


Pass list

Results

Finalisedresults

Signed passlist


Results

Signed passlist

Results

Results andpass list

Envelope

Envelope



Steps in Logicalisation

• Step 1- Rationalise Data Flows– Remove all reference to physical items eg.

tickets, order form etc.– Replace with actual data being passed eg. order

details


Rationalise Data Flows

Physical

• Application form• Student record• Assignment and exam

marks• Stamped addressed

envelope• Pink top copy

Logical

> Application details> Student details> Student marks

> Request for results

> Order details


• Step 2 - Rationalise Data Stores– An entity must be represented by one and only one

data store• a logical data store may represent a logical grouping of

entities

– Remove any reference to a physical storage facility and prefix with D identifier

• eg. Appointments Diary becomes Appointments

– transient data stores should be removed (but may reappear in the required physical DFD, eg. for batch processing)



COURSE

SUBJECT STUDENT

MODULEENROLMENT

MITIGATINGEVIDENCE

belongto

contain

be enrolledon

contain

be assessedby

relateto

achieve

relateto

be presentedby

present

Entity Model for Current System


Data Store Entities

M1: Course document Course, Subject

M1/1: Subject results file Subject, Student, Module Enrolment

D2/1: Spreadsheet results file

M4/1: Course results file

Subject, Course, Student, ModuleEnrolment

Subject, Course, Student, ModuleEnrolment

M2/2: Mitigating evidence Student, Mitigating evidence

M4/2: Envelope file Course, Student

Physical Data Store/Entity cross

reference


Guidelines for Data Stores

• Logical data stores typically contain entities:– that are created at the same time– that are linked via relationships– whose attributes form part of the same

major input/output data flows


COURSE

SUBJECT STUDENT

MODULEENROLMENT

MITIGATINGEVIDENCE

belongto

contain

be enrolledon

contain

be assessedby

relateto

achieve

relateto

be presentedby

present

Entity Model for Current Student Assessment System

D1

D2


Logicalised Data Store / Entity

Cross referenceData Stores Entities

D1: Courses Course, Subject

D2: Students Student,Module Enrolment,Mitigating Evidence


• Step 3 - Rationalise bottom level processes– Remove all reference to location or responsibility, i.e.

leave it blank– Remove processes which re-organise existing data

e.g. sorting or collating data• Processes 4.1 and 4.2 are no longer needed

– Where a process remains clerical or exists simply for physical reasons, remove it. Replace with an external entity, eg. Process 1 - preparation and marking of assessments by Subject Tutor

• Subject Tutor becomes an external entity



Rationalise Bottom Level Processes

• Remove processing that cannot be automated i.e. a process which requires subjective or expert decisions e.g. awarding a degree– Process 3, moderate and finalize results by Board of

Examiners• reviews student results• takes account of mitigating evidence• arrives at a consensus decision

• the “doers” of such processes become external entities of the system so Board of Examinersw (BOE) becomes an external entity


Rationalise Bottom Level Processes

• If data is unaltered by a process replace it with a data flow

• Remove any physical aspects of the process– e.g. add reservation in red becomes confirm

reservation• Combine processes which perform the same

function or duplicated processes• Combine related processes (often connected

by direct data flows between them)


Guidelines for Processes

• Split over-complex processes into simpler processes

• Regroup “bottom level” processes– by function rather than location

• Reconstruct the resultant top level DFD


*

File studentmarks &

mitigatingevidence

1

*

Publishresults

2

*

Store andretrievedata for

BOE

3

SubjectTutor

Student

ExamsOffice

Boardof Examiners

StudentsD2

CoursesD1

StudentsD2

Student marks

Mitigatingevidence

Request forresults

Results

Results

Results


Course details


Requestindicator

Results

Course details

Course details


Results

Level 1 Current Logical DFD of System


Set andMark

Assessments

Subj Tutor1

*

Collatemarks for

all students

Yr leader2

*


results

BoE3

Producepasslist

Sch Admin4

Course documentM1

Timetabler

Examsoffice

Examsoffice

Student

Headof

School

Regulations

Regulations



Finalisedresults

Timetable

Completedexamination

Examinationpaper

AssignmentCompletedassignment

Markedassignment

Mitigatingevidence

Results



Pass list

Signed passlist

Level 1 Current Physical DFD of System


Further Reading

• Lejk and Deeks– An Introduction to Systems Analysis

Techniques• Chapter 9 Logicalisation

• Philip L Weaver– Practical SSADM version 4 Pitman

Publishing• Chapter 3 p 112-115

unit 13 university of sunderland comm1b information systems analysis 1 identifying system...

Documents

information system systems

existing system

old system

present system

new system requirements

business system options

potential system improvements

technical system options