The Semantic Web Week 14 Module Website: Lecture (SHORT): OWL PIZZAS Practical (LONGER): Getting to know Protégé-2000.
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The Semantic Web Week 14 Module Website: http://scom.hud.ac.uk/scomtlm/chs2533 Lecture (SHORT): OWL PIZZAS Practical (LONGER): Getting to know Protégé-2000 WITH OWL
Recap n Ontologies are a kind of ‘knowledge base’ which emphasise the capture of domain structure (rather than eg operational knowledge) n Building knowledge bases involves Knowledge Engineering – the process of acquisition, formulation and validation of knowledge n Protégé is a knowledge engineering tool – chiefly for formulation. Last week we saw how to use it in its general form. This week you will use it with its OWL plugin.
This Week.. n Lecture: We will look at one well documented OWL ontology – OWL Pizzas from the University of Manchester (they’ll be cold by the time they get here ;-) ) n Practical: You will use Protégé with the OWL plugin and an OWL Pizza tutorial
Recall OWL / Description Logic n We have the open world assumption – things may be true UNLESS it is specifically stated or can be inferred that they are not. So obvious assumptions have to be recorded – especially ‘disjointness’ between classes
Knowledge Acquisition and Validation VALIDATION of a formal model is best done in a ‘DIVERSE’ way – using static and dynamic methods….
The Pizza Application n The requirement is to encode an ontology that captures the structure of types of Pizzas.The Protégé tool assists in a kind of method for knowledge acquisition, and helps eliminate simple syntax and structural errors n Next week we will see that inference tools are used in Ontology building u for validation purposes – to check that the ontology is accurate and self-consistent. Recall that subsumption is the inference mechanism in DLs. u to help (re-) structure the class hierarchy.
Knowledge Acquisition without function? n Its difficult to try to capture knowledge without considering FUNCTION Eg you have to write a LIST class in a programming language. How do you do it? By first considering WHAT FUNCTIONS are required on it! -checks for null(list)?, operations for adding and selecting members ETC For an ontology, we have no strong functional requirements for it is harder…
Acqusition method for Ontologies in OWL … n Enter classes and subclasses. u eg Pizza, PizzaBase, PizzaTopping, CheeseTopping n Specify disjointness properties between classes u eg MeatTopping and VegetarianTopping. n Enter properties and subproperties u Eg hasIngredient, hasBase, isIngredientOf n Specify characteristics of properties such as functional, inverse, transitive, symmetric. u eg “isIngredientOf” Is it functional? Transitive? Can it be both? Does it have an inverse? n Enter Property Domain and Range n Enter Property Restrictions
Practical Work n Open the OWL tutorial PDF document on http://www.co-ode.org/resources Work through Chapter 4 (page 19->) of this – showing you how to enter pizzas into Protégé NB n there are NO wizards on the Sun implementation of Protege (there were acting up and had to be slain by the technicians) so you have to enter some stuff ‘long hand’ n Protégé is a bit slow and clunky
NEXT week – n we will look at the OWL + the RACER reasoning system (technology permitting)