Reconstructing Ontologies from Fragments Derek Sleeman, Sik Chun (Joey) Lam, Wamberto Vasconcelos 2 Oct 2005

Overview Motivations Overview of Architecture (In)consistency Issues Experimental Plan Future Work

Motivations Reusing Ontologies Existing ontologies often cannot be read by ontology editors because they are deemed to be inconsistent: E.g., contain errors such as circularity Integrating Ontologies How to integrate / merge two or more standalone ontologies

Current ontology editors Results of IMPORTING an ontology containing a circularity error SWOOPProtégé-OWLOilEdWebODE Detected StatusA, B and C are displayed as equivalence Displays infinite loops between A, B and C Displays an error messages; importing is aborted Same as OilEd A is-a B C

Overview of Architecture (1) Subsumption relationship heuristics Possible is-a relationships in fragments Reasoner O1O1 O2O2 OnOn … O1O1 O2O2 Ontology fragments Use heuristics to choose 2 ontology fragments O2O2 O 2 O 1 O1O1

Overview of Architecture (2) Consistent? Yes No O2O2 O 2 O 1 O1O1 O2O2 O 2 O 1 O1O1 the least bad sub-ontology the best sub-ontology O 1 O 2 O 1 O 2 Removal Inconsistency Heuristics O 1 O 2

Experimental Plan Run experiments where knowledge engineers are asked to reconstruct an ontology from fragments, and remove resulting inconsistencies Three aspects of ontologies will be focused on: Topological Properties Structure of concepts Removal of inconsistencies

Experiment (Topological properties) The topological properties are important when searching for the best concept to integrate with. The average length of paths (deep or shallow hierarchies). The average number of siblings (broad or compact hierarchies)

Experiment (Structure of Concepts) A range of strategies for comparing two nodes for a concept/sub-concept relationship Features of Concepts (in RDFS) Quantification Restrictions (in OWL) Cardinality Restrictions (in OWL) Conjunction, Disjunction, Negation (in OWL)

Compatible concepts/sub-concepts Node A can be added to node B as a sub-concept if it is more specific (so additional features can be introduced). {Also node A needs to be similar to its planned siblings.} Suppose Node B is {publication-number integer; Volume integer; has-parts B5} Compatible sub-concepts would be: {publication-number 2005; Volume integer; has-parts B5} {publication-number integer; Volume 999; has-parts B5} {publication-number 2005; Volume 999; has-parts B5; has-author: Simon} Incompatible sub-concepts would be: {publication-number 2005A; Volume integer; has-parts B5} {publication-number integer; Volume integer; has-parts B6}

Compatible concepts/sub-concepts Additional comments In general there will be a number of places where nodes (& fragments) could be placed Are there efficient strategies for finding these? If a user is insistent that a node must be a sub- concept, despite apparent inconsistencies then this probably means that the specifications of either, or perhaps both, the nodes are wrong & need revision.

Experiment (Removal of inconsistencies) Inconsistencies occur when fragments are integrated; we plan to use a reasoner to detect these inconsistencies. In this experiment, inconsistent concept(s) in the ontology are highlighted, & the subject is asked how to resolve the inconsistency cardinality restrictions quantification restrictions NB Manchesters studies on explanations of inconsistencies in ontologies

Removal inconsistencies (1) Cardinality Restrictions In the following case, Male and Female are disjoint, and HappyParent is inconsistent, the subject is asked how to resolve this inconsistency. Parent OneChildParent Tired Parent MaleFemale HappyParent Human hasChild 5 1 1

Removal inconsistencies (2) Quantification Restrictions In the following case, Cow is Vegetarian which does not eat part of Animal, but its subclass Mad_Cow eats part of Animal. The subject is asked how to deal with this Vegetarian Cow Mad_Cow Animal Sheep eats part_of eats Brain

Future Work: an Extension Here we plan to handle multiple fragments Example: Ordering of integration now becomes an issue (Needs a more sophisticated algorithm & heuristics.) O1O1 O2O2 O3O3 is-a O1O1 O2O2 O3O3

Comments / Questions?

(In)Consistency Issues Applying heuristics to select fragments to integrate: All are consistent Choose the best option Some are consistent; some are inconsistent Choose the best option All are inconsistent Choose the least bad option O2O2 O 2 O 1 O1O1 the least bad sub-ontology O 1 O 2 O2O2 O 1 O1O1 the best sub-ontology O 1 O 2