Formal ontology as interlingua the SUMO and Word

Formal ontology as interlingua: the SUMO and Word. Net linking project and global Word. Net Adam Pease and Christiane Fellbaum Presenter: 吳怡安

Outline 2. 1 Word. Net 2. 1. 1 Types and instances 2. 1. 2 Formal vs linguistic relations 2. 1. 3 Lexical vs conceptual ontologies 2. 1. 4 SUMO 2. 2 Principles of construction of formal ontologies and lexicons 2. 3 Mappings 2. 4 Interpreting language 2. 5 Global Word. Net 2. 5. 1 The Interlingual Index 2. 6 SUMO translation templates

2. 1 Word. Net • Word. Net is a large lexical database for English • Basic unit: synset (cognitively equivalent synonyms) • Eg. {vacation, holiday} • Definition: leisure time away from work devoted to rest or pleasure • Sentence: "we get two weeks of vacation every summer” • 117 000 synsets • Relations • Super-subordinate relation (also called hyperonymy, hyponymy) • Transitive: armchair-furniture • Part-whole relation (Meronymy, holonym) • verbs towards the bottom of the trees express increasingly specific manners characterizing an event (communicate-talk-whisper)

2. 1. 1 Types and instances • Word. Net distinguishes among Types (common nouns) and Instances (specific persons, countries and geographic entities). • armchair is a type of chair • Barack Obama is an instance of a president • Instances are always leaf (terminal) nodes in their hierarchies. • However, other distinctions are lacking. • Brother and architect as Types of persons • Dwarf is a kind of person • One can refer to the same person as both a dwarf and an architect • Roles often refer to professions or functions associated with a person or temporary states (such as patient)

2. 1. 2 Formal vs linguistic relations • One could extend the a few relations of Word. Net to all the hundreds of relations that are found in a formally specified logical theory like SUMO. • Eg. part-of, before. Or. Equal, authors etc. • Relating informal linguistic notions with more formal ontological relations • Specifying complex relations that cannot be captured explicitly as simple links

2. 1. 3 Lexical vs conceptual ontologies • Lexicon can be defined as the mappings of concepts onto words. • There are structural gaps where the geometry of the relations would require a word, yet where the language does not have one • the class of wheeled vehicles (like cars and motorbikes) vs vehicles that run on rails (trains, trams) • Crosslinguistic differences in lexicalization patterns • kinship relations • Existing words do not fully reflect the inventory of concepts that is available, so one can use the non-lexical ontology such as SUMO

2. 1. 4 SUMO (1) • The Suggested Upper Merged Ontology (SUMO) is a formal ontology stated in a first-order logical language called SUO-KIF. • Upper ontology includes general notions in commonsense reality • time, spatial relations, physical objects, events and processes • Mid-Level Ontology (MILO): more specific • Domain ontologies cover a dozen specific areas • world government, finance and economics, and biological viruses

2. 1. 4 SUMO (2) • 1, 000 terms and 4, 000 axioms (which includes 750 rules) • Term: named concept • Axiom: any statement in logic • Rule: a particular kind of axiom that has two parts: an antecedent and a consequent • http: //www. ontologyportal. org (<=> (earlier ? INTERVAL 1 ? INTERVAL 2) (before (End. Fn ? INTERVAL 1) (Begin. Fn ? INTERVAL 2)))

2. 1. 4 SUMO (3) • In a formal ontology, it is solely the axioms as mathematical statements that give the terms their meaning. • The meaning of the terms can be tested for consistency automatically with an automated theorem prover. • The names of terms in SUMO are just convenient labels, so there are no synonymy.

2. 2 Principles of construction of formal ontologies and lexicons • Lexicon must accurately reflect the inventory and use of words in a given language. • Neither eliminated nor ‘missing’ words • By contrast, an ontology is an engineered product. • Naming, categorization, creation of the terms are at will • Every lexicalized concept should be covered by a term. • Synonymy is not needed • The names of the terms could be replaced by arbitrary unique character strings and their meaning would still be the same. • In a formal ontology, meaning is determined only by the formal axioms.

2. 3 Mappings (1) • Two phases: • First, mapping just SUMO itself to Word. Net. • Three types of mappings were employed: rough equivalence, subsuming, and instance. • Equivalence: { artificial_satellite } to ARTIFICIALSATELLITE • Subsuming: { elk } to HOOFEDMAMMAL • Instance: { george_washington } to HUMAN • Second, for each synset that occurred three or more times in Sem. Cor, we also created a new concept in the MILO if one did not already exist in SUMO.

2. 3 Mappings (2) • Limitation: a single mapping from a lexical entity to a formal term does not fully capture the meaning of some lexical items • Eg. { Continue } can refer to many unrelated types of Process • referenced in the context of previous sentences • One would need a more complex relation structure to express the semantics of this lexical item

2. 4 Interpreting language • Deep semantic interpretation of language • Eg. ‘Brutus stabbed Caesar with a knife on Tuesday. ’ (exists (? S ? K ? T) (=> (and (instance ? X Knife) (instance ? S Poking) (capability Cutting ? X instrument)) (instance ? K Knife) (instance ? T Tuesday) (agent ? S Brutus) (patient ? S Caesar) (time ? S ? T) (instrument ? S ? K)))

2. 5 Global Word. Net • Vossen (1998) coordinated the effort to create eight European wordnets that follow a common design and are interlinked via an Interlingual Index (ILI) • Wordnets exist in over 40 languages spoken around the world at present. • Interconnected wordnets hold great potential for crosslinguistic applications. • Shedding light on commonalities and the differences in the ways languages map concepts onto words

2. 5. 1 The Interlingual Index • there are language-specific ‘lexical gaps’ • there are differences in the ways languages structure their words and concepts • The ILI initially consisted of all English Word. Net synsets. Each international wordnet either links its synsets to the matching synsets in the ILI or adds a synset that is not yet in the ILI. Each synset in the language-specific wordnet has at least one equivalence relation to an entry in the ILI. • Due to the limitations of lexical ontologies, many wordnets have also been linked to SUMO.

2. 6 SUMO translation templates • In order to make SUMO more understandable, they created a system that performs rough natural-language paraphrasing of the formal axioms (<=> (earlier ? INTERVAL 1 ? INTERVAL 2) (before (End. Fn ? INTERVAL 1) (Begin. Fn ? INTERVAL 2))) A time interval happens earlier than another time interval if and only if the end of the time interval happens before the beginning of the other time interval.

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