IPT home IPT A Virtual Approach by Peter Whitehouse
Quick Links:
 
 
ORM home
Information and Intelligent Systems Social and Ethical Implications Human Computer Interaction Software and Systems Engineering eXercise Files Course Outline and Assessment A-Z of Geeky Acronyms Terrace Work Program 2004 Sillybus FAQ = Frequently Asked Questions Help
 
 

Representing Knowledge

Alternative Conceptual Representations

NIAM is not the only conceptual (knowledge) representation technique.

Presented here are 2 others. All techniques have at their core the need to represent information precisely and unambiguously. Any method has its' PRO's and CON's.


'Z'

'Z' is not a programming language, rather it is a preciseMATHEMATICAL specification language, relying heavily on SET NOTATION.

The 'Bank' schema below represents the BASE STATE of a database that tracks customers in a bank.

a Z base state schema

In brief, the first section (the pre-conditions) state that there is a set of OPEN tellers, a teller is BUSY if the teller is serving someone, there is a queue waiting to be served, there are others in the bank. The second section of the Bank base state schema specifies that busy tellers are a subset of those open, it is not possible to be in the queue and being served at the same time, nor is it possible to be in the queue and roaming around the bank, or being served and roaming. Further it states (redundantly?) that the number of people in the queue is the same as the number of places in the queue

a Z base state schema

This second schema is termed a TRANSITION or STATE SCHEMA, and in this case it represents the process where a teller says "next please". The first section (the pre-conditions) states that this action produces a change in the BANK BASE STATE SCHEMA, and that an input (the teller number) is required as input to the process. The remainder of the schema states that the teller must be one of the ones that is open, the teller is not allowed to be busy already, there must be someone in the queue, the person at the head of the queue moves to be busy with the teller, the queue reforms after the departure of the head person, the number and id of tellers open remains unchanged, and the others roaming around in the bank remains unchanged.

'Z' appears exhaustive (indeed to record all process in a typical bank would require many dozens of individual schemas). It is, however very precise in describing the behaviour of objects in the system being specified.

'nuf said.


E-R Diagrams

an ER diagram

Entities are rectangles, relationships are diamonds, attributes are ellipses, KEYS are underlined.

Advantage: slightly intuitive, fairly easy to draw

Disadvantages : table design trial and error, many types of constraints are unable to be specified, lack of referential integrity, lack of inter-fact type constraints. Relies on clear differentiation between entities and roles (which presents a problem as sometimes a role becomes an entity as in the case of a nested fact type)

.....fin conceptual modelling (yay!)

 

wonko@wonko.info
©Copyright t 1992..2017+. Edition 25.150117
wonkosite
Creative Commons License
This work is licensed under a
Creative Commons Attribution-NonCommercial-ShareAlike 2.1 Australia License
.