ELH 1 Entity Life Histories Model the system from the viewpoint of how information is changed. – Diagrammatic representation of the life of an entity from.

ELH 1

Entity Life Histories

• Model the system from the viewpoint of how information is changed.

– Diagrammatic representation of the life of an entity from creation to deletion

– Permitted sequence of events that can change an entity occurrence

– Part of the Entity-Event Modelling technique

• Purpose of Entity Life Histories– Analysis - to show that all the update processing and states of

entity occurrences have been considered– Design - to help in program specification– Leads to Effect Correspondence Diagrams

for each event show the correspondence between its effects on entities

used to define Update Process Models (program designs)

ELH 2

Events in the Life of an Entity

• An event causes a consistent and complete set of changes to information held in the system.

• Each occurrence of an entity will be affected by one or more events

M. Moneybags Account

Account opened

Cash Deposit £2000

Cheque Cashed £20

Direct Deposit £1000

Cheque Cashed £20

Direct Deposit £2000

P. Penniless Account

Account Opened

Pay deposit £500

Cheque Cashed £200

Cheque Cashed £300

Cheque Cashed £300

ELH 3

Sample ELH for a Bank Account

• Entity Life Histories show all the events that have an effect on an entity during its life

• Diagram is generic

i.e. valid for any account at the bank

Account Life

Account Deletion

Bank Account

Account Closure

Account Opened

Credit Debit

Balance Change

*

o o

ELH 4

EVENT

• Something that triggers a process to update system data

• May have an effect on several entities

• Matrix shows effects of events on entities

Account Opened Credit Debit

Account Closure

Cus

tom

er

Ban

k A

ccou

nt

Tra

nsac

tion

Events

Entities

C C M C M C M

Effect of event on entity is:

Creation CModification MDeletion D

Account Deletion D

ELH 5

ELH Notation

Account Life

Account Deletion

Bank Account

Account Closure

Account Opened

Credit Debit

Balance Change

*Nodes Events having an Effect on the Entity

Entity name

o o

ELH 6

Sequence

• 'A' will always be the first to occur, followed by 'B', 'C' and 'D' in that order

• No other sequence is permitted

• No indication is given of time intervals between the boxes in a sequence

A B C D

Entity X

ELH 7

• Events or nodes that are alternatives at a particular point in the entity life history

• Selection shown by a box with a circle in the top right corner

• Occurrence of entity X created by any one of three events: E, F or G

Selection

A B C D

E F G

Entity X

o oo

ELH 8

Selection (continued)

• If one of the options is “do nothing,” a 'null' box may be added:

– 'Null' box does not represent an effect or node– Indicates nothing is happening– If the 'null' is selected, the life continues directly to the next

node or event

E F G

A

o o o o

ELH 9

• Event or node may be repeated any number of times at the same point in a life

• An occurrence of the iteration must be complete before the next begins

• Shown by an asterisk in the top right hand corner of a box

• Event H may affect the entity any number of times

NB. 'Any number of times' includes zero!

Iteration

A B C D

E F G H *

Entity X

o o o

ELH 10

Parallel Structures and Quits and Resumes

• Occasionally required

• Can manage without, but useful to simplify structure

• Used in the situation where events or nodes occur in no predictable sequence

• Does not show concurrency

• Shown as a horizontal parallel bar on the ELH diagram

ELH 11

Parallel Structures

• Event 'N' may affect the entity a number of times during the sequence of K, L and M.

• Node 'I', representing the sequence, and the node 'J', representing the iteration, are shown under the parallel bar

Entity X

DA B C

F G H

I J

K L M N

*

*

E o o o

ELH 12

Diagram Without Parallel Structure

• The previous ELH can be drawn without the parallel structure

• Iteration of 'N' must be repeated several times

• Parallel Structure is probably easier to understand

Entity X

* * * *

A B J K J L J M J D

NNNNHGFE*o o o

ELH 13

Quit and Resume

• Quit from one part of an ELH to Resume in another part

• If the quit event occurs, then instead of processing the event marked with the Q, the life jumps to the quit event which is marked R

• After event B occurring, instead of the normally occurring next event C, event E can occur

• Possible event sequences are: abcbcde, ade, abe, abcbe

• Known as a disciplined conditional quit

Y

A 1 D E

2

CB

R1

Q1

*

ELH 14

Illegal Unconditional Quit

• Unconditional quit where the quit event must always be followed by the resume effect

• Different from the disciplined conditional quit shown previously

• Can always be avoided by redrawing the structure

Illegal

in SSADM

Entity X

E F

JI

HG

NMLK

A B DC

*

o o o *

ELH 15

Equivalent Diagram to SSADM Standards

• Two new nodes, P and Q, ensure that each parent node has children of only one type.

JI

K L M N

F

E G H

Entity X

B C

D

A

P

*

Q

*

o o

o o

ELH 16

Random Quits and Backward Quits

• Quit backwards (reversion) to Account Life if Account Re-opened (Q1)

• Random Quit on Customer Death to Death Structure (R2)

Account Life

Bank Account

Account Closure

Account Opened

Balance Change

Credit Debit

*

Account Deletion

Possible Re-open

Account Re-opened

Death Structure

Customer Death

Customer Deletion

Q1

R2

R1

Q2: Quit from anywhere on Customer death to R2

o

o

o

o

ELH 17

Combining the Components

• A node cannot be a “parent” to more than one type of structure.

• This structure is incorrect because:

—Node X, combines (“parents”) a selection (A and B) with a sequence (A, B, and 2)

—Node 2 combines a selection (C and 4) and an iteration (F) with a parallel structure

—Node 4 combines two iterations (D and E) with a sequence.

X

BA

F4

2

C

ED

OO

OO

*

*

*

ELH 18

Corrected Version to SSADM Standards

• Node X parents a sequence;

• Node 2 parents a parallel structure;

• Node 3 parents a selection;

• Node 4 parents a sequence;

• Nodes 5, 6, and 7 parent iterations.

X

3BA

21

65

F4C

7

ED

o

oo

o

*

**

ELH 19

Effect Qualifiers (Optional Effects)

• Where one event can affect an entity occurrence in two or more ways

• Effect Qualifiers (shown in brackets) distinguish between two different effects of the same event (Debit)

e.g. The event “Debit” will have different processing if account is overdrawn rather than in credit

Account Life

Account Deletion

Bank Account

Account Closure

Account Opened

Credit Debit

Balance Change

*

Debit (account overdrawn)

(account in Debit

credit)

Optional Effects

ELH 20

Entity Roles (Simultaneous Effects)

• When one event occurrence affects more than one entity occurrence (of the same type) in different ways

E.g. a Bank Account may be closed by transfer to another account

• One event occurrence “Transfer”, two entity occurrences affected

– account being closed and account being opened

• Simultaneous effects of one event shown by role names in [square brackets]

Account Life

Account Deletion

Bank Account

Account Closure

Account Opened

Cheque or Cash Credit

Transfer [New Account]

Transfer [Closed Account]

Final Withdrawal

o o o o

Entity Roles

ELH 21

Operations

• Operations added to Entity Life Histories

• Operations show the processing performed on the data

• Each operation must change an attribute value in the entity occurrence or a relationship occurrence

• Operations follow a specified syntax (considered later)

• Operations identified by number in small square box attached to entity

• Operations list shown beside Entity Life History

Bank Accoun

t

Account Opene

d

Account Life

Account Closure

Account

Deletion

Balance Change

*

Credito

Debito

Operations List

4. Replace Balance using Balance + Credit Amount

5. Replace Balance usingBalance - Debit Amount

1. Store Keys 2. Store remaining attributes

3. Gain Transaction

6. Store Date Closed

3 4 3 5

1 2 6