Transcript Entity Event Modelling Entity Event Matrix, Entity Life History, Effect Correspondence Diagram

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)
– separately for each entity (Entity Life History)
– separately for each event (Effect
Correspondence Diagram)
First, let’s recap
• Joe’s Yard has a current logical DFD
• A set of Requirements
• A Logical Data structure
Current Logical DFD
Customer
Docket &
Payment
1
Shop
Pick
and
pay
Signed docket
4
Check
and
supply
*
Supply needs
Joe
*
docket
M3
2
Yard
Supply order
Issue
supplies
3
*
M1
Order
book
Accept
supplies
*
Docket
5
Shareholders
financial
report
Produce
financial
report
M2 Supply receipts
*
Supply invoice
Supply payment
Supplier
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
Customer
Staff
Supplier
Customer Id
Customer Name
Customer Address
Staff name
Staff no
Staff role
Supplier Id
Supplier Name
Supplier Address
Amount Owed
Docket
DocketNo
Order Date
*Customer Id
DocketPaidSig
DocketRcvdSig
*Staff no
Stock
SupplierOrder
Stock Code
Stock Description
Unit Price
*Supplier Id
UnitCostPrice
Stock level
Reorder level
*Supplier Id
SupplierOrderNo
SupplierOrderDate
DeliveredDate
Order Line
*DocketNo
*Stock Code
QuantityRequired
SupplierOrderLine
*SupplierOrderNo
*Stock Code
StockRequired
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 Matrix
r
c
c
r
r
c
r
c
r
r
m r
Supplier
Order Line
c
Supplier
Order
c m
m
m
c/r
Supplier
Order Line
r
Stock
Staff
c
Docket
Customer
Entity /
Event
Pick and Pay
Issue Supplies
Accept Supplies
Check and Supply
Produce Financial
Report
Lodge Requests
Contact Customers
Re Requests
m
c/r c
c
r r
c/r c
r
c
Issue Video
Video Return
M
M
M
M
C
D
Reservation Request
M
C
C
New Tape
Collect Reservation
M
M
C
Tit
le
Re
se
rva
t io
n
Ac
to
r
Lo
an
Entities/Events
Bo
rro
we
r
Ta
pe
Entity / Event Matrix
D
C
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
• “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
•
SEQUENCE - left to right
SELECTION
- either or
ITERATION
*
Stock Entity Life History
OPERATION LIST
Stock
create
Check and
Supply
amend
delete
Sell stock
Restock
Issue Supplies
Accept Supplies
Lodge Request
Standard Payment ELH
not Joe’s Yard!
payment
Cheque created
Payment entered
Authorised
Issued
Printed
Removed
cashed
lost
expired
reconciled
cancelled
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
• These are used to ensure that the Entity Life
Histories are completed satisfactorily.
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.
• 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.