1. System Modelling
Events

2. Thinking in terms of events
System modelling nearly always starts with the concept of events
System is considered to be a...
that responds to external events
black box

3. Event Modelling Why use event models? Useful for…
Focusing attention on system at a high level
Ignoring details of the system
Thinking from a users point of view
Decomposing system into logical parts for further analysis

4. Event Types We have three types of events External Events
Temporal Events
State Events

5. External Events
Occur to the system from an external source. Initiated by an external agent….
Person
Organizational unit
External system

6. Temporal Events Occur to the system…
as a result of reaching a certain point in time
may be periodic or non-periodic
may result in some automated response from the system

7. State Events
Triggered within the system as a result of…
some other process reaching a certain state
Sometimes it is difficult to distinguish between state and temporal events.

8. Starting Event Modelling
A Library System.
Pictorial representation of external events

9. Starting Event Modelling
A Library System.
Pictorial representation of external & temporal events

10. Producing an Event List
A Library System.
External Event List for Library System
Customer wishes to register with the library
Customer wishes to borrow a library item
Librarian wants to view the book catalogue
Etc.
Temporal Event List for Library System
Daily check for overdue items …
Etc.
State Event List for Library System
Notify customer that reserved item is awaiting collection …
Etc.

11. Producing an Event Table
Event table can be used…
Useful to examine each event in more detail and note additional information such as…
appropriate system response
description of any activity that should be carried out for the event.

12. An Event Table A Library System. Event Description Event Trigger
Source of Trigger
Actions
Output Response
Output Destination
Customer wishes to register with the library
Registration request
Customer
Enter new customer into borrowers database process
Confirm registration

13. Starting Event Modelling
A Library System.
Event description - a description of that event.
Event trigger - anything that informs the system that data must be processed in some way. Usually a more detailed description of the event.
Source of trigger - specifies an external entity for an external event or a point in time for a temporal event.
Actions – processes that must be carried out by the system in response to the event.
Output response - description of any output from the system
Output destination – where the output is to go

14. An Event Table A Library System. An incomplete event table
Event Description
Event Trigger
Source of Trigger
Actions
Output Response
Output destination
Customer wishes to register with the library
Registration request
Customer
Process new customer details. Update circulation database
Confirm registration
Customer wishes to borrow a library item
Item loan request
Check item status. Check borrowers status. Update borrowers circulation and catalogue database
Confirm loan
Customer wishes to view the book catalogue
View book catalogue request
Fetch book details from catalogue database
Display the catalogue
An incomplete event table

15. An Event Table Create an Event Picture and Event Table
Now It’s Your Turn
Create an Event Picture and Event Table
For Southwark College Learning Centre