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Principles and Practice of Ontology Development: Making Definitions Computable Chris Mungall LBL
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Why make definitions computable? Doing the work all by yourself is hard, boring and error prone Automate using reasoning Bonus: – Makes the definitions easier for humans – Enables better visualization
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Biology is modular, most ontology classes are compositional distal phalanx proximal phalanx autopod foot hand p dp pp dpf dphpph ppf pf ph (adapted from diagram by David Hill and Joel Richardson)
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History “Cross-products” – Hill, D. P. and Blake, J. A. and Richardson, J. E. and Ringwald M: Extension and integration of the gene ontology (GO): combining GOvocabularies with external vocabularies. Genome Res 2002 Formal Concept Analysis Description Logics 1980s-present – Galen – Rector et al – GONG – Wroe, Stevens et al
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Logical definitions Genus-differentia form – Text definition is genus-differentia form Distal phalanx of hand: – “A distal phalanx that is part of a hand.” – or “A distal phalanx[ID:2] that is part of a hand[ID:3].” – OWL: ‘distal phalanx of hand’ EquivalentTo ‘distal phalanx’ and part_of some hand – OBO-Format [Term] id: ID:1 ! distal phalanx of hand intersection_of: ID:2 ! distal phalanx intersection_of: part_of ID:3 ! hand
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Editing logical definitions OBO-Edit – Cross-product tab Genus Differentia – Parent Editor select links to make them ‘intersections’ Protégé 4 – Equivalent Classes Enter expression
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Using a reasoner Given: – ‘distal phalanx of hand’ EquivalentTo ‘distal phalanx’ and part_of some hand – ‘phalanx of hand’ EquivalentTo phalanx and part_of some hand – ‘distal phalanx’ is_a phalanx A reasoner can infer that: – ‘distal phalanx of hand’ is_a ‘phalanx of hand’ dp dph ph
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Uses of a reasoner Ontology authoring – Time saving Automatically inferring is_a polyhierarchy – Quality Control detecting inconsistencies Data integration and discovery – Less applications… so far
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Reasoners OBO-Edit – Rule Based Reasoner OWL Reasoners (Protégé 4) – Pellet – FaCT++ – HermiT
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Difference between OBO and OWL reasoning OBO format expresses a subset of OWL – We thought this would be enough for most users – But this turned out not to be true – E.g. Lacks part – See talk later today Sufficient for basic anatomical classification
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Modularity and external ontologies Modularity principle: – Multiple orthogonal ontologies – Use classes from O 1 as building blocks in O 2 – E.g. astrocyte differentiation anucleate cell BUT: Can pose problems for large external ontologies – CHEBI – PRO
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Import application can choose to follow import chain – if it doesn’t, then there are dangling references the full import closure can be large! GO-BP CL imports ontology based application
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Large Import Closure GO-BP CL ontology based application PRO CHEBI GO-CC AO
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Bridge files BP-xp-CL BP CL basic application more advanced application current solution used by NIF, GO
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MIREOT - Minimal Information for Retrieval of External Ontology Terms BP CL (full) CL subset copy current solution used by OBI, PRO, hemo-CL ontology author “MIREOT”s in subset of external ontology
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Deploying cell.obo Typical User – inferred links materialized – external ontology links removed Advanced User – asserted links only – external links present – minimal external classes included
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Ontology publishing pipeline cell_edit.obo GO/PRO/e tc subset cell_public.obo GO/PRO/e tc subset cell_basic.obo cell_edit.owl GO/PRO/e tc subset cell_public.owl GO/PRO/e tc subset cell_basic.owl reasoner filter obo2owl
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Summary Many ontologies are seeing the benefits of using computable definitions – e.g. fly anatomy – GO slow to adopt, lots of legacy issues to work out Better to employ them from the outset – DC_CL – Hemo_CL
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