Ontotherapy: or how to stop worrying about what there is. Yorick Wilks Computer Science University of Sheffield, UK

1. 1 Ontotherapy:or how to stop worrying about what there is.Yorick WilksComputer ScienceUniversity of Sheffield, UK EUROLAN August 2003

2. 2 Ontology used to be about What things there actually ARE, but... Now is mostly about how to structure knowledge in general The latter work comes in at least two forms: Ontologies from NLP people, e.g. Nirenburg�s Mikrokosmos, designed for NLP Formalisms/Ontologies/Description logics for scientific knowledge (e.g. Fensel, Horrocks, Gruber); the old AI-KR task renamed.

3. 3 Ontology as knowledge structure. These two groups are quite disjoint and this talk is about the former and their critics, like Guarino. The latter group are not about ontologies any more than about KR in general (of which ontology proper is only a part).

4. 4 Points of the talk Efforts to formalise the sort of world knowledge needed for NLP may well be ultimately pointless, but worth a try. The criteria offered for �cleaning up� existing structures: May make a unified hierarchical content representation impossible Ignore the degree to which representations inevitably remain language-like.

5. 5 More points to be made Structures like WordNet, whatever their faults, contain vital information as objects of study, cf. Rogets Thesaurus Much pretended clarification of WordNet is as muddled as what it attacks. Such attacks ignore: The paradox of explicitness of information The possible value of uninterpretable structures e.g. Open Directory, Schvaneveldt�s networks.

6. 6 As a sanity control remember... The widespread use of Open Directory with Physics ISA Astronomy ISA Physics (where ISA is uninterpretable). Schvaneveldt�s Pathfinder Networks and the empirically supported representation of human expertise:

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9. 9 Points in the second part of talk: The �promiscuity-fecundity� tradition about what there is basically correct; BUT this view is not butressed by self-contradictory uses of FOPC; Nor by appeals to possible worlds where they all contain the same entities; Because there are real disputes about what there is; And the answer is individual belief systems, ontologies and lexicons.

10. 10 What are the basic structures? Linnaean ontologies: interpretable as set inclusions ? (but no problem with individual members ?) I.e. clear values of ISA. Hierarchies of concepts in ambiguous relations to sets of individuals (but with their own ? sets). Thesauri: words (known ambiguous) clustered under a major concept to give classes of words with no formal relation.

11. 11 Wordnet has all these in one structure, plus�.. Linnaean inclusion: ungulates--horses Simple subsets: shoes--tennis shoes Set membership: painters--Picasso Abstract membership: Carcompany--Ford Whole-part: Body--hand--finger ?Concept--component: Islam -- Sunni ?Concept-subconcept: Physics--Gravity

12. 12 Wordnet has lots of conceptual mother-daughters of the latter kind: Religion Islam Bhuddism Sunni Shia But these cannot be interpreted/modelled by sets of or individual people (WordNet tries this for one sense!), buildings, parts etc.

13. 13 But Wordnet is not an ontology And not because its special notion of synonymy (synsets) cannot be an ontological relation at all! But because it mixes in all the above kinds of relations,only some of which can be ontological� IF one takes the view that ontological relations must be more or less Linnaean (I.e. unambiguously about the world)

14. 14 That is what real ontologies in use are like (I.e Linnaean): E.g. Rolls Royce Jet engine parts (AKT) E.g. Drugs (Glaxo Smith Kline) AND you can refer the concept as well as its instantiations (e.g. US Prez is male and over 35) BUT they are all unpacked as sets of individuals AND the Knowledge Base is more than the ontology

15. 15 WordNet may not be an ontology But it has ontological subtrees. NOR is it really a thesaurus, which does not have set theoretic hierarchies either but does, unlike Wordnet, have major categories of subsumption (cf. game issue) without any top-level organization (Though Roget wanted to give biological structure!).

16. 16 Wordnet is often referred to as an ontology, which confuses matters But it has repeated lexical items in different senses (I.e. that defines senses) which is the clear mark of a thesaurus An ontology, by contrast, claims its symbols are not words but interlingual or language-free concept names and unique. This is an old line, indefensible, and the weakest link in the ontology story--in WHAT sense is a predicate used in CYC?

17. 17 On this last (fundamental) issue Nirenburg, S. and Wilks, Y. (2001) What�s in a symbol? Journal of Experimental and Theoretical AI. The paper was in the form of a Greek dialogue and my character argued that, no matter what formalists say, the predicates in formalisms that LOOK LIKE English words, REMAIN English words Strange that anything so obvious should be so strenuously denied.

18. 18 Guarino wants to �firm up� WordNet but will the medicine kill the patient (OntoClean)? His critique of WordNet: chiefly the mixing of types: apple given as fruit and food (only former necessary) window given as panel and opening--cannot be both says G. person given as living thing and causal agent (not necessarily the latter says G).

19. 19 Guarino�s solution is Identity Criteria for all concepts: ICs make things what they are and allow their reidentification (= sufficient conditions for identity, later shifted to necessary conditions, which he thinks are easier to express) You cannot then hierarchically link concepts with different ICs (e.g. ordered sets are NOT sets). Hence person cannot be subsumed by physical object.

20. 20 But can we have a useful hierarchy if a person cannot be seen to be a physical object? As in the interpretation of: �Smith tripped and fell on the guinea pig and killed it� cf. Jokes are when persons fall under physical laws (Bergson?)

21. 21 Does he really mean this? �..person should not be subsumed by physical object (as a physical object, a body has persistence conditions different from a living being). Yet..these ISA links exist in WordNet� (Guarino, LREC 1998).

22. 22 Guarino�s �reform� of Mikrokosmos on these principles social event communication event mental event physical event perceptual event social event communication event mental event perceptual event physical event lower simpler figure has (vertical) ontological levels (Guarino LREC 1998)

23. 23 But can this system be set up consistently with his principles? Surely mental events and perceptual events do not have the same identity criteria���as any child philosopher knows?!

24. 24 It gets worse��. On any (Aristotelian or) Linnaean hierarchy, a genus is distiguished from the term above by differentia BUT these must lead to different IC s e.g. Canary ? Bird. But canaries are not individuated by the same criteria as birds So canaries cannot be subsumed by birds!!

25. 25 So can a Guarino ontology be populated at all, by anything? What are such ontologies for? Do non-Guarino ontologies not allow the inferences and linkages we need for NLP? NB Guarino does not, of course, intend that Canaries/Birds subsumptions are not in an ontology--my question is how, on his published claims, can he avoid the conclusion in a non-arbitrary way.

26. 26 The constant danger of higher nonsense in this area of formalization: �A piece of coal is an example of a singular whole. A lump of coal will still be a topological whole, but not a singular whole, since the pieces of coal merely touch each other, with no material connection. It will therefore be a plural whole� (Gangemi, Guarino et al. P.4) Perhaps they mean �pile�?

27. 27 Why is that kind of stuff so unhelpful? It takes as technical terms, on which to base a theory, words of a language (English) which will not and cannot bear the interpretations required. This is the same problem as the predicates themselves in semi-formal theories (cf. Nirenburg). They cannot express or admit the senses of the words they use (cf. Wordnet OK).

28. 28 Nothing new here�.. �The Languages which are commonly used throughout the world are much more simple and easy, convenient and philosophical, than Wilkins� scheme for a real character, or indeed any other scheme that has been at any other times imagined or proposed for the purpose� Horne Tooke (quoted by Roget at the end of his 1862 Preface to his Theasuarus).

29. 29 The possible link from Guarino�s levels to regular polysemy Guarino�s ontological levels have been linked to the phenomenon of �regular polysemy� (Pustejovsky, Buitelaar et al.): mental event physical event social event

30. 30 This might be to cover classic regular polysemy cases like: Ford = company, car, ?management Pustejovsky does not want many entries for these; just one plus lexical rules However, any link from phenomena like this to �ontological levels� would require that the �multifunctional entity� (e.g. Ford) would appear in more than one place. Possible in a thesaurus or WordNet but anathema in an ontology?!

31. 31 Old fallacies show that the issue of concepts and individuals are not easily resolved�. My car is a Ford (?) and Ford is a car company (?) therefore My car is a car company Error of non-transitivity of E ? Error of ambiguity of �Ford� which is regular polysemy here, not concept vs. instance (though it is close to that, too!)

32. 32 Guarino�s analysis rests on the most conservative of principles: That there are necessary and/or sufficient conditions for the application of a concept (cf. Quine, Putnam��cats from Mars!) That the concept/individual (cf. intension/extension, sense/reference) distinction is straightforward, in terms of Fregean conditions of application of a term or concept.

33. 33 Will these methods �rescue� Wordnet and does it need it? Unclear such ontologies can be set up for general domains (G admits finding conditions for IC s is very hard) Is there any evidence that such an ontology would do any better for inference and retrieval than: uninterpretable structures e.g. Open Directory Schvaneveldt�s associationist networks WordNet?

34. 34 Empirical NLP work can bear on these issues: Cutting top level hierarchies in LDOCE (Guthrie, Cowie and Wilks) Extracting knowledge hierarchies and facts from text automatically to populate ontologies (Brewster, tradition of Marti Hearst) Perhaps Ontologies, Knowledge Bases, Lexicons etc. must all be populated (semi-) automatically if there is to be progress?

35. 35 Empirical text-extracted Ontologies bring up two issues: Anticipated (subsumption) gaps; expected from data sparseness in general--some obvious X-ISA-Y�s are never stated. Some X-ISA-Ys are untrue, or could be said to reflect individual or wrong-shared orntologies e.g. Tomato-ISA-Vegetable, Strawberry-ISA-fruit. NB Gruber�s original definition of (modern) ontologies as shared conceptualizations (cf. invididual ontologies below).

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37. 37 Notice there is no pretence here that these are abstract primitives: They are English word senses (except for the cycle-breaking top node) subscripted with their sense in LDOCE see Wilks, Cowie and Slator (1996) Electric Words, MIT Press.

38. 38 Second part: on what there actually is�.. As well as the 2500 year old problem of: are there concepts as well as individuals�. Cf. �There�s no such thing as Society, only families and their members� (M.Thatcher) Hirst follows Hobbs in favour of ONTOLGICAL PROMISCUITY Ontological Fecundity would be better (no couplings, just more things!)

39. 39 Who wants how much? Meinong wanted golden mountains and round squares�.roughly Hobbs� position. Quine said �To be is the value of a bound variable� but didn�t want �the possible man in that doorway� (because he didn�t believe modal logic was logic). Yet couples sometimes speak of the baby they might have had, and sometimes even name it (cf. WAOVW?).

40. 40 Hirst wants all Hobbs wants but also�... Wants a predicate to state that things REALLY EXIST Is this dangerous? (1 bn. Hindus think Rama really exists; 60% of UK population think Common Law Marriage exists; 65% of US population thinks German was almost the US national language!)

41. 41 Do lexical/ontological structures need a position on this issue? Probably not, but the issue of how to express the status of �the strike� in: �The negotiations prevented the strike� doesn�t go away--you just cant express it in FOPC It poisons calculi like the FOPC to put both E and EXISTS in a single expression, as Hirst and his critics do. Cargo Cult logic!!

42. 42 My own hunch�.. Fecundity/Promiscuity must be right about what there is�. But the issue is not in the public knowledge bases But in individual ones�� Contrary to all attempts at formalization, individuals really differ about their beliefs as to what things there are�...

43. 43 My favourite example: Vanbrugh the C18 architect (Blenheim Palace) and Vanbrugh the C18 playwright (The Relapse). are IN FACT the same person but few people have this fact represented! Hirst assumes we must settle for a possible worlds account where all Worlds have the same individuals in.

44. 44 Computational models of possible worlds are not sensible But models of the ontologies, lexicons, knowledge bases of individuals are..�with different memberships as well (unlike PWs) They must all differ but be similar enough for us to communicate effectively (like language itself!). We also model each others� structures (cf. Problems of �mutual� knowledge/ontologies vs. individuals and Gruber�s shared knowledge strcutures as ontologies. See A. Ballim and Y. Wilks (1991) Artificial Believers, Erlbaum.

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46. 46 Or, if you want a more ontolog(ist) plausible example, over events not persons Horrocks was simultaneously invited to Sheffield by two groups, on two successive days, unbeknown to each other! Each inviter know of one invitation, but there were in fact two, and Horrocks assumed there was only one, since the alternative was so implausible. One inviter noticed this: consider communication problem where Horrocks and the Smart-inviter disagree about how many events there are.

47. 47 Much of the time we are vague or coconspiratorial about existence: Who can remember whether it is MacBeth or Hamlet who actually existed? If on a quiz for $1m and asked �Who was Sherlock Holmes� brother?� it is inappropriate to reply �neither he nor his brother existed�. Nonexistent people and events can be marked without an EXISTS predicate if one insists.

48. 48 Presupposition may be better seen as individual ontology/belief claims Strawson�s point (against Russell) that one who says: �The present King of France is bald� Is not making a false existential claim but stating a presupposition. OR, indicating to us what belief/ontology model we should build for the speaker.

49. 49 Conclusions In ontology as structure and as population, we should always resist Cargo Cult logic: uses of logic that will never yield computable structures or effective inferences. Ontological fecundity is inevitable, as individuals differ (particularly about what there is) and we must model them to understand.

50. 50 Conclusions 2 Ontological and lexical resources can themselves be objects of research (cf. Masterman�s search for Roget�s unconcious, Buitelaar and Peters on WordNet regularities) Attempts to clean up resources may make them impossible to construct. Better an imperfect linguistic resource than none.

51. 51 Conclusions 3 Ontological and lexical resources do not differ in principle and the fact WordNet is mixed does not disqualify it from use. Attempts to clean up resources should perhaps be done by automating their construction as best we can. It may however be tidier to segregate operational ontologies as those of the Linnaean type (under set inclusion).

52. 52 Conclusions 4 Formal ontologists use the word simply mean AI Knowledge Bases and are confusing the issues. Possible worlds can never help computationalists but individual models almost certainly will. Empirical activity is relevant to resource construction and is always its goal. Mental hygiene in ontologies may be hard and even self-defeating but we should try.

53. 53 References Nirenburg Nirenburg, S. & Wilks, Y., (2001), What�s in a symbol: ontology, representation and language. Journal of Experimental and Theoretical AI Fensel Gruber Horrocks Guarino Schvaneveldt