Entity event modelling
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Entity Event Modelling. Entity Event Matrix, Entity Life History, Effect Correspondence Diagram. Entity-event modelling. An entity may be effected by several events. An event may effect several entities . This can be represented by a matrix (Entity Event Matrix)

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Entity Event Modelling

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Entity event modelling

Entity Event Modelling

Entity Event Matrix,Entity Life History,Effect Correspondence Diagram


Entity event modelling1

Entity-event modelling

  • An entity may be effected by several events.

  • An event may effect several entities.

  • This can be represented by

    • a matrix (Entity Event Matrix)

    • separately for each entity (Entity Life History)

    • separately for each event (Effect Correspondence Diagram)


First let s recap

First, let’s recap

  • Joe’s Yard has a current logical DFD

  • A set of Requirements

  • A Logical Data structure


Current logical dfd

Current Logical DFD


Set of new requirements

Set of New Requirements

  • “We want Joe to have a stock level on his stock, so that we know what needs to be ordered.”

    • No new process

  • “We want Joe to know who his customers are, so that he can tout for repeat business.”

    • New process – mail shot

  • “We want Joe to be able to lodge requested items, so that he can make a decision on whether to stock them in the future or so that he can order them on demand.”

    • New processes – lodge requests, contact customers re requests.


New logical data structure

New Logical Data Structure


Entity event matrix

Entity-event matrix

  • List all entities across the top of the page.

  • List all events (system functions) down the side of the page.

  • Fill in the matrix as follows:

    • If an event creates an entity, mark with C.

    • If an event deletes an entity, mark with D.

    • If an event modifies an entity, mark with M.

    • All entity columns should have at least one C, D and M/R.


Entity event matrix1

Entity / Event Matrix


Entity event matrix2

Entity / Event Matrix


Entity life history

ENTITY LIFE HISTORY

  • An Entity life history consists of a tree, the top node of which is the entity.

  • The next level contains nodes indicating the organisation of events.

  • The almost lowest level contains nodes representing the individual events which change the entity.

  • The lowest level contains the processing operations which achieve the effects of the higher nodes.


Ssadm ideal

SSADM ideal

  • “For each entity, make out an entity life history”

  • In a real situation

    • Identify entities that

      • Effect a lot of other entities

      • Change states a lot


Entity life histories

Entity Life Histories

  • SEQUENCE - left to right


Selection

SELECTION

- either or


Iteration

ITERATION

*


Stock entity life history

Stock Entity Life History


Standard payment e lh not joe s yard

Standard Payment ELH not Joe’s Yard!

payment

Cheque created

Issued

Removed

Payment entered

Authorised

Printed

cashed

lost

reconciled

expired

cancelled


Steps in development

Steps in development

  • Make out a 'normal' life: Creation, amendment, deletion

  • Include complications - irregularities

  • Include all known events

  • Check importance of timing of attribute creation / modification / deletion

  • Check alterations to entity's relationships

  • Anything else missing from ELH?


Effect correspondence diagrams

Effect Correspondence Diagrams

  • These are used to ensure that the Entity Life Histories are completed satisfactorily.


Construction

Construction

  • List all entities effected (updated) by an event.

  • Draw as for LDM, including only entities and relationships effected by the event.

  • If one event can effect an entity in different ways, use selection boxes, listing the effect roles in the box.


Entity event modelling

  • If one event can effect several occurrences of an entity, use an iteration box, describing the set of occurrences in the box.

  • Entities required by the event for enquiry purposes can also be listed, along with the reasons for enquiry and attributes needed. Entities needed more than once for different reasons, will be displayed more than once, but boxed together.


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