The Semantic WebWeek 15Reasoning with (and Visualising) OntologiesModule Website:

http://scom.hud.ac.uk/scomtlm/chs2533Practical :Protégé-2000 WITH OWL:

Work through Protégé tutorial up to page 73

Recap

Protégé-2000 is a Knowledge Acquisition Tool that helps one build up Ontologies in OWL. We can create hierarchies of is-a classes, properties, and necessary conditions for class membership.

The Pizza example is useful for learning about ontologies as it contains a wide range of structured and composite types.

Question..

Protégé is a tool which helps people build ontologies in OWL – that is enter knowledge in a form that can be used in the Semantic Web.

Question: Can non-computer experts use it?

CONTINUED: Developing ontologies in OWL: “Partial” and “Complete” Definitions

Partial = Necessary Condition Complete = Necessary and Sufficient Condition

Example: set {2,4,6,8,10,12}Necessary condition for membership: even number[but 14 is even but not a member..]Sufficient condition for membership: = 2N, where 0 < N < 4[but 12 is a member that is not = 2N]Necessary and Sufficient Condition:Even number between 2 and 12 inclusive.

OWL: “Partial” and “Complete” Definitions

OWL abstract syntax:

Class(a:Pizza partial

restriction(a:hasBase someValuesFrom (a:PizzaBase)))

FOL:

Ax Pizza(x) => Ey hasBase(x,y) & PizzaBase(y)

PizzasPizzaBase

Things that have at least one PizzaBase

hasBase

Necessary and Sufficient Classes..We need sufficient conditions - If we only have

necessary conditions then we can never state for definite that an instance is a member of a class.

Eg

CheesyPizza(x)

Pizza(x) &

Ey hasTopping(x,y) & CheeseTopping(y)

For-All Restrictions

Vegetarian condition…

Ay hasTopping(x,y) => (CheeseTopping(y) V

VegetableTopping(y))

..but also need an existential condition saying there exists at least one topping…

For-All Restriction gives Complete Defn:

VegetarianPizza(x)

Pizza(x) &

Ay hasTopping(x,y) => (CheeseTopping(y) V

VegetableTopping(y))

NB there are other possible defns ..

VegetarianPizza(x)

Pizza(x) &

not (Ey hasTopping(x,y)&MeatyTopping(y)) &

not (Ey hasTopping(x,y)&FishyTopping(y))

Reasoning- Subsumption Used to RE-CLASSIFY an asserted hierarchy. The

re-classification is called the inferred model. Used for Consistency checking – can every class

defined have some instances?

Eg

IS-A IS-A

DISJOINT

Another Example: The Martians Application

1. GreenMartians C AntennaeMartiansA Martian has antennae IF it is green.2. A_has-child.Antennae C Friendly A Martian is friendly to humans IF all of its children have antennae. 3. E_has-parent.Green C Green A Martian is green IF at least one of its parents is green.

Step 1: Define Martian class, and Green, Antennae, Friendly subclasses.

Step 2: Create subclasses of Friendly and Green with necessary and sufficient conditions

= A_has-child.Antennae and E_has-parent.Green respecivelyStep 3: Create has-parent and has-child propertiesStep 4: A necessary condition for a Martian is that it has at least one

parent

The Martians Application- Asserted Model

The Martians Application

Step 5:

Run the classifier

a) Use OWLViz – the asserted model is the facts that have been asserted.

b) The inferred model should show that all green Martians friendly (the hierarchy has been changed)

The Martians Application – Inferred Model

Practical Work –

1. Continue with the protégé – owl tutorial. You should be up to page 49 now. This week do pages 50 – 73.

Under “Project” configure Protégé with “OWLViz”

2. Put Martians into Protégé, and do reasoning using Protege