1. Identifying system improvements: Logicalisation
Information System Analysis COMM1B
Unit 13
Technique - Normalisation
LDM - top down
Normalisation - more mathematical and rigorous - scientific - BOTTOM UP
arrives at relationships via a different route.
Developed by Edgar Codd in 70’s for IBM
-Applied principles of mathematical set theory and algebra to the organisation of data
-data previously stored in ad hoc fashion
-data files often mirrored paper documents, or the way data was entered onto the system
-data duplication rife causing redundancy
-data duplication causes problems with maintenance and flexibility
Looked at system to decide on entities and then determine relationship between them. Not very precise, and may be puzzled as to why some entities are linked to others.
Discussed the sorts of relationships - business relationships
Relationships come about because of the way businesses operate
eg A CUSTOMER places an ORDER
therefore the customer is related to an order in a business sense.
Looking at a totally different approach

2. 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.

3. 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

4. System Modelling 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
This technique called NORMALISATION
Will look at normalisation by examining steps 1, 2, 3, and 4
Will find out what these strange terms mean as we go through the lecture.
Normalisation is a bottom up approach
looks at the DATA ITEMS in a system
Group similar data items together - ENTITIEs
Relationships developed between entities by looking at the data items present in more than one entity
Coming at the problem from the opposite direction from entity modelling (LDM) 1

5. Current System Model Current Physical Model Current Logical 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

6. Stages of Systems Analysis and Design
Investigate and analyse system
Current PHYSICAL System Model
Perform Logicalisation
Current LOGICAL System Model
Add New System Requirements, Consider Business System Options
Required LOGICAL System Model
Add Implementation Details, Consider Technical System Options
Required PHYSICAL System Specification

7. 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

8. Simple Example of Physical level 1 DFD
Party details 1
You M1
Diary
Discuss party details and record interest
Person details
Party enquiry
Party details M2
Phone directory
Colleague
Party invitation 2
You
response
Invite guest by telephone
Tickets * 3
You M3
Address Book
Produce and send out tickets to party M1
Diary

9. Logicalised level 1 DFD Colleague Party details Party Data 1
Communicate and record party data
Party/contact data
contact details D2
Contact Data

10. 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

11. Level 1 Current Physical DFD

12. Level 2 Current Physical DFD

13. Level 2 Current Physical DFD

14. Level 2 Current Physical DFD

15. 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

16. 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

17. Steps in Logicalisation
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)

18. Entity Model for Current System

19. Physical Data Store/Entity cross reference

20. 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

21. Entity Model for Current Student Assessment System

22. Logicalised Data Store / Entity Cross reference

23. Steps in Logicalisation
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

24. 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

25. 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)

26. 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

27. Level 1 Current Logical DFD of System

28. Level 1 Current Physical DFD of System

29. Further Reading Lejk and Deeks Philip L Weaver
An Introduction to Systems Analysis Techniques
Chapter 9 Logicalisation
Philip L Weaver
Practical SSADM version 4 Pitman Publishing
Chapter 3 p