Semantic Network ComplexitySemantic Network ComplexityAndAnd

Metathesaurus Maintenance Metathesaurus Maintenance

Stuart Nelson, MDStuart Nelson, MD

““Dr. Ad Hoc”Dr. Ad Hoc”

Role of Semantic NetworkRole of Semantic Network

Categorize the Concepts of the Categorize the Concepts of the MetathesaurusMetathesaurus

Model RealityModel Reality Model the ContentsModel the Contents

Semantic Network ProblemsSemantic Network Problems

Structural ConsiderationsStructural Considerations Limited UseLimited Use Poor Type AssignmentsPoor Type Assignments

Problematic AssignmentsProblematic Assignments

Inconsistent AssignmentsInconsistent Assignments ““Wrong” AssignmentsWrong” Assignments Strange Type Co-OccurrencesStrange Type Co-Occurrences

Why Do These Things Why Do These Things Happen”Happen”

Stupid Editors?Stupid Editors? Poor Selection of Types?Poor Selection of Types? Inherent Complexity?Inherent Complexity? Poor ManagementPoor Management

Where Does Complexity Arise, Where Does Complexity Arise, Or Why Is This So Hard?Or Why Is This So Hard?

Formalization GapFormalization Gap Duality of Central NotionsDuality of Central Notions Boundary PhenomenonBoundary Phenomenon Nelson’s LemmaNelson’s Lemma

Formalization GapFormalization Gap

Natural Language UnderstandingNatural Language UnderstandingPattern RecognitionPattern Recognition

Recall and Reliable MemoryRecall and Reliable MemoryFormal ReasoningFormal Reasoning

A Different AspectA Different Aspect

Humans Have Difficulty With Formal Humans Have Difficulty With Formal NotionsNotions

Formal DefinitionsFormal Definitions• A set of ordered pairsA set of ordered pairs• The set of first coordinates of the The set of first coordinates of the

ordered pairsordered pairs

Duality of Central Notions Duality of Central Notions

Cancer – Process or Object?Cancer – Process or Object? Gene – Locus or Sequence?Gene – Locus or Sequence? Finding - Event or Relationship?Finding - Event or Relationship? Waves and ParticlesWaves and Particles

Boundary Phenomenon Boundary Phenomenon

Definitional CharacteristicsDefinitional Characteristics Necessary and Sufficient AttributesNecessary and Sufficient Attributes

Nelson’s LemmaNelson’s Lemma

Greater Number of BoundariesGreater Number of Boundaries

LEADS TOLEADS TO

Greater Number of Borderline CasesGreater Number of Borderline Cases Overlapping “Extents”Overlapping “Extents”

Process of Semantic Type Process of Semantic Type AssignmentAssignment

Default Assignment from SourceDefault Assignment from Source Some Sources (MeSH) have STYsSome Sources (MeSH) have STYs Human Review of Concept StatusHuman Review of Concept Status Human Review of Semantic TypesHuman Review of Semantic Types

Practical ConsiderationsPractical Considerations

Achieving ConsistencyAchieving Consistency Managing ChangesManaging Changes Distribution of STY AssignmentsDistribution of STY Assignments Understanding Source MeaningsUnderstanding Source Meanings URU CriteriaURU Criteria

Achieving ConsistencyAchieving Consistency

See Nelson’s LemmaSee Nelson’s Lemma Internal (Self) ConsistencyInternal (Self) Consistency Editorial VariabilityEditorial Variability Inconsistent RulesInconsistent Rules

• Use ParentUse Parent• Use Several ChildrenUse Several Children

Managing ChangesManaging Changes

How Many Seconds per Change?How Many Seconds per Change? How Many Records to Edit?How Many Records to Edit? What Can Be Done Algorithmically?What Can Be Done Algorithmically? Resources AvailableResources Available

Distribution of AssignmentsDistribution of Assignments

Overlapping MeaningsOverlapping Meanings Facet-Based TypingFacet-Based Typing Inconsistent RulesInconsistent Rules

Understanding Source MeaningsUnderstanding Source Meanings

Definitions RareDefinitions Rare ““Contextual Understanding”Contextual Understanding”

• HierarchiesHierarchies Most Vocabularies A Set of Most Vocabularies A Set of

Engineering CompromisesEngineering Compromises

Prime Directive Prime Directive

Respect the Meaning in the SourceRespect the Meaning in the Source Names Lack Face ValidityNames Lack Face Validity Reification of Relationships Reification of Relationships

RespectRespect

Reality - Names and Rules Only Reality - Names and Rules Only Reflect Our UnderstandingReflect Our Understanding

Sources - Reflect The View of The Sources - Reflect The View of The SourceSource

URU Criteria For TypesURU Criteria For Types

UnderstandableUnderstandable ReproducibleReproducible UsableUsable

ChallengesChallenges

AnalysisAnalysis• Useful algorithmsUseful algorithms• Time InvolvedTime Involved• Assessing BenefitAssessing Benefit

TrainingTraining• Establishing Business RulesEstablishing Business Rules• Testing ConsistencyTesting Consistency