1. Chris Russell O2.41d 02920 41 6431 crussell@cardiffmet.ac.uk
Business Analysis
Entity Life History
Chris Russell
O2.41d
Lecture BA14 Entity Life History

2. Lecture BA14 Entity Life History
Session schedule
Business Analysis Schedule
Academic Year
Semester 2
Week
Topic 1
Introduction 2
Investigate situation: rich picture, context diagrams 3
Consider perspectives: types of participation, CATWOE, Power-Interest, Thomas-Kilmann 4
Analyse needs 1: Use Cases 5
Analyse needs 2: structured techniques 6
Define requirements 1a: SSADM 7
Define requirements 1b: SSADM
EASTER 8
Define requirements 2: UML 9
Generic assignment feed-forward and task review 10
Balance good enough software against quality costs; Prioritise requirements 11
Assignment submisison
Lecture BA14 Entity Life History

3. Activities and Paradigms
Investigate Situation
Consider Perspectives
Analyse Needs
Define Requirements
Socio-technical
Rich picture
CATWOE
Types of participation
Thomas-Kilmann
Power-Interest X
Functional
Level 0 diagram
Structured techniques
DFD, ERM and ELH
Object-Oriented
Context diagram
Use Cases
Class and Sequence diagrams
Lecture BA14 Entity Life History

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Contents
Mapping functions to entities
Entity Life History constructs:
Sequence
Iteration
Selection
Constructing an Entity Life History
Advanced features of Entity Life Histories
Entity Life Histories in Select
Logical Data Structures in Select
Lecture BA14 Entity Life History

5. Mapping functions to entities
Entity Life Histories enable functions (taken from the DFD) to be mapped against entities (taken from the LDS)
In addition, they represent the key features of structured decision techniques:
Sequence
Iteration
Selection
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Sequence
All ELHs will contain a sequence of events, read from left to right. The first event will always show the creation of the entity, and the last box will show the event which deletes the entity.
Lecture BA14 Entity Life History

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Iteration
Iterations are used to illustrate cases where an event can effect an entity occurrence more than once and is represented by an asterisk in the top right hand corner of the box.
Lecture BA14 Entity Life History

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Selection
This indicates a choice between more than one event and is indicated by a circle in the top right hand corner of the box.
Lecture BA14 Entity Life History

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Selection can also be used to illustrate optional effects by employing a null box.
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Development of ELH
The development of entity life histories is carried out in the following stages:
identify an initial list of events which affect the entities 
using the LDS diagram as a reference point, document the effect of those events on each entity
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Stage 1 involves the creation of a matrix which cross refers entities to the events which effect them. The list of entities forms one axis of the matrix and is taken from the logical data model of the system.
The list of events forms the other axis and this comes from the functions in the system (from the DFD). For every entity in the matrix, it is necessary to determine whether an event creates, modifies, or deletes the entity, and this is entered on the matrix as C (create), D (delete) or M (modify).
Lecture BA14 Entity Life History

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Entity/Event matrix
Lecture BA14 Entity Life History

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Stage 2 involves developing the ELH for each entity.
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Checking the matrix
When the entity/event matrix is thought to be complete, it should be checked as follows:
·       does every entity have at least one creation and one deletion event? If not then the reasons should be investigated, and any missing events identified.
·       if an entity is not updated, is there a reason for this?
·       does every event affect at least one entity? If it does not then there is an error which must be rectified.
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Exercise
Draw an entity life history for the entity STUDENT given the following entity/event matrix
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Parallel lives
entity x
birth event
mid life
death event
main life
parallel life
event F o
event M o
event N o o
transactions
transaction
change details
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Quit and resume
There are occasions when events happen out of sequence.
A notation called 'quit and resume' is used to denote this.
By the leaf that shows the departure from sequence, a 'Qn' is placed, and against a leaf where the lifecycle is re-commenced, an 'Rn' is placed.
the n denotes a corresponding numeric character.
The Q (or Quit) indicates a point where, given a specified exception condition occurs, the structure is left.
The R (or Resume) indicates the point at which it is rejoined.
Lecture BA14 Entity Life History

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State indicators
A state indicator is a single byte attribute that is changed each time the entry is updated.
It takes the form of a numeric digit, and is written under each leaf of the ELH to reflect the values. Each time an event affects the entity, the value of the state indicator is changed to indicate the current state of the records.
Thus the state indicator value means that the entity occurrence is at a particular point in its life.
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Entity x
Event A
Event B
Deletion
event
Birth event
-/1
1/2
2/3
3/-
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The rules for adding state indicators help to explain the diagram:
1. each leaf has 2 values, a 'before' and an 'after' value. The value is conventionally numeric, starting from 1 at creation, and increasing for each new event that
changes it.
2. the first and last values, i.e. on creation and deletion are null values
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3. on an iteration, the valid previous indicators include the new valid indicator
4. if a value is not to be changed, as in a parallel life event, or if any previous value is valid, this is shown as an asterisk (*)
5. when using a 'quit and resume', the state indicator is set before the quit, so the resume box will show the new value as a valid previous value
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This week, next week
Complete remaining ELH tasks
Lecture BA14 Entity Life History