1. The Semantic Web – WEEK 11: Description Logic + OWL Featuring..MAD COWS

2. The Semantic Web Recap Description logic is a restricted form of FOL which has special operators / constructors for ‘concepts’ – that is classes of individuals A concept or class is the set of individuals x that satisfy some Wff(x) DL expressions are more compact than FOL – eg there are NO quantified variables In DL we have ‘concept expressions’ which evaluate to sets of individuals eg A intersect B and wffs as in classical logic eg A subset-of B Two important DL concept expressions are E_relation.property and A_relation.property

3. The Semantic Web Description Logic Recap - Martian example u Green ss Antennae All green Martians have antennae. u A_has-child.Antennae ss Friendly A Martian is friendly to humans if all of its children have antennae. u E_has-parent.Green ss Green A Martian is green if at least one of its parents is green. u has-child = has-parent- u Green ss Friendly? Are all green Martians friendly?

4. The Semantic Web Reasoning - Subsumption In FOL the main form of reasoning is to find whether Wff A logically follows from Wff B. In Description Logic it is SUBSUMPTION. Simple: A,B are concept expressions. A subsumes B if A is a superset of B Examples of a small ontology – what subsumes what? Person Person or Animal Person with > 3 degrees Person with > 2 degrees Lecturer Lecturer with a male partner Lecturer with a female partner Vegetarian Vegan with > 3 degrees

5. The Semantic Web Reasoning – CWA In databases, logic programming, AI the main type of reasoning used is: The Closed World Assumption Which means: If something isn’t asserted true, and you can’t prove its true, then ASSUME it is false.

6. The Semantic Web Reasoning –OWA In Description Logic (and OWL) we use the The Open World Assumption wffs that are true are wffs that are asserted true or wffs you can prove true. Eg ? Assume that with our ontology example above we were also told that “Fred is-a Person with > 2 degrees” QUERY Fred is-a Person? CWA= Yes OWA=Yes QUERY Not ( Fred is-a Lecturer) CWA = Yes OWA = No (not known) NB that does not mean that OWA deduces that Fred is-a Lecturer!

7. The Semantic Web Description Logic Useful for giving a semantics to ‘OO design’ or ‘semantic net’ diagrams ISA Swallow Bird = Swallow subset-of Bird CarBlack HAS-COLOUR = ??????????????

8. The Semantic Web OWL Is now the STANDARD ontology language OWL is in fact 3 languges: - OWL Lite - OWL DL (..description logic) - OWL full..and TWO forms: - OWL abstract - OWL/RDF syntax

9. The Semantic Web OWL DL – MAD COW example n ObjectProperty – declares a property. Its global domain and range may also be fixed n Class – declares a class “partial” means the definition is (only) necessary “complete” means necessary + sufficient n Restriction – means “the class such that” ie it declares that an anonymous class is about to be defined n R someValuesFrom P – means “E_R.P” n R allValuesFrom P – means “A_R.P” n minCardinality/maxCardinality specify the limits of class sizes

10. The Semantic Web Summary n DL uses Subsumption and OWA in its reasoning (more next term!) n DL is a nice way to formalise diagrammatic representations n OWL-DL is a wordy version of DL

11. The Semantic Web Exercises –week 11 ISA student lecturermodule Research-student PTlecturerr ISA ENROLSTEACHES-ON SUPPORTS 1. Make the meaning of the diagrams precise by stating them in Description Logic and First Order Logic. Make any reasonable Assumptions you need to. Person Name: String Birth-place: Town 2. Create a subsumption diagram for the following concept expressions Students Students or Bus-Drivers Students with 2 jobs Students with 1 or 2 or 3 jobs Students who are Bus-Drivers Students with a male friend who is-a doctor Students with a male friend with > 1 degree Students with a male friend who is-a Bus- Driver Students with a friend who is-a doctor Students with every male friend who is-a doctor 3. Use a search engine to find both OWL/RDF and ‘OWL abstract’ versions of Manchester’s MAD COW example (search on MAD COW OWL !). Study the two versions of the mad cow ontology to see the connections between the two OWL forms of expression. 4. Try to turn parts of the the MAD COW handout into DL or even FOL