title: Definitions and qualifiers in SNOMED CT.
abstract: An important feature of SNOMED CT is post-coordination, which is enabled by the SNOMED CT representation specifying whether a relationship is a defining or a qualifier relationship. In this paper the use of qualifier relationships in SNOMED CT is analyzed, as well as the extent to which qualifiers interact with defining relationships, so that pre-coordinated concepts can also be post-coordinated.
  
  
  
  The July 2007 release of SNOMED CT was imported into a database. Analyses were performed by querying this database.
  
  
  
  Qualifier relationships occur in 10 out of 61 types of attribute relationships, and it is shown that generally pre-coordinated concepts cannot be constructed by applying post-coordination using qualifier relationships. Most of the qualifier relationships have generic target concepts, making it possible to construct concepts which are not clinically sensible. A logic-based representation is proposed to overcome the drawbacks of the current model.
  
  
  
  Defining and qualifier relationships both enable post-coordination in SNOMED CT. Introducing qualifiers for more types of relationships, and using qualifier relationships with more specific target concepts will further improve post-coordination in SNOMED CT.
authors.affiliation: Department of Medical Informatics, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands. r.cornet@amc.uva.nl
authors.forename: Ronald
authors.initials: R
authors.lastname: Cornet
mesh_terms: D003198:Computer Simulation; D016208:Databases, Factual; D006801:Humans; D008128:Logic; D016015:Logistic Models; D008490:Medical Informatics; D039061:Systematized Nomenclature of Medicine; D009626:Terminology as Topic