Since 1990 CEN TC 251 and ISO TC 215 have developed an approach named Categorial Structure. It is a logic-based language that aims at standardising the upper level structure of a terminological model rather than agreeing on a reference clinical terminology or on a language-independent biomedical ontology. Since 2000 methods, tools and techniques based on upper level ontology and description logic formalism have been developed in the Semantic Web and the bio-ontology communities. The objective of this paper is to analyse the relation between the two approaches in order to promote the complementary use of ontology and structured information model tools in the harmonisation between biomedical terminologies and to improve semantic interoperability.
Standardisation in Health Informatics started in the U.S.
with the HL7 user group. The European Standard Body
CEN TC 251 WG2 (Comité Européen de Normalisation
Technical Committee 251 Working Group 2) and later the
International Organisation for Standardization (ISO) TC 215
WG3 elaborated and developed a standard approach for
biomedical terminology named Categorial Structure
(CAST)
Since 2000, ontology-driven methods, tools and techniques
have been developed in the Semantic Web and the
bioontology communities. Numerous research groups have
moved towards upper-level ontologies (ULO) in order to
manage the organization, integration and interoperability of
biomedical information in a more principled way. Not only
in research circles, but also in the medical terminology
business, there is an increasing belief that using formal
ontology approaches helps improve the quality of
terminological systems. Description logics
The objective of this paper is to analyse the relation between
the two approaches, viz. upper-level ontologies (ULO) vs.
Categorial Structure (CAST), to ease the use of applied
ontology to harmonise different biomedical terminologies.
In a first part we present the definition and specifications of
the CAST standard methodology
The CEN Categorial Structure was defined, as presented
in
Deed, Interventional Equipment and Lesion; (3) The semantic links are has_object, has_sub_surgicaldeed, has_means... has_site, (3.1) has_object is authorised between Deed and Human anatomy or Interventional Equipment or Lesion; (3.2.) has_site is authorised between Interventional equipment or Lesion and Human anatomy;
(3.3) has_means is authorised between Deed and Human anatomy, Interventional equipment or Lesion; (3.4) has_sub_surgicaldeed Deed and Deed; (4) The minimal constraints required are: is authorised between (4.1) A Deed and has_object shall be present; (4.2) Human anatomy shall always be present either with the relation has_object or with a has_site; (4.3) Use of Lesion shall be restricted to macroscopic lesion and to cases where it allows differentiating the procedure from procedures using the same deed and the same human anatomy; (4.4) When has_sub_surgicaldeed is used, the Deed on the right side of the semantic link must be conform to the rules 3.1, 3.2 and 3.3.
3.1
BFO
Basic Formal Ontology (BFO) is a philosophically inspired
top-level ontological framework
BFO is divided into two main parts: Continuants (entities
which continue to exist through time), and Occurrents
(entities which exist in full in a single instant of time). It
provides a coherent and unified understanding of basic
ontological entities that are fundamental to describe a science-based
reality, and it allows integrating domain terminologies
especially biomedical ones. BFO v1.1 includes 39 classes. This
version does not include any relations, an ontology of
relationships such as OBO Relation Ontology (RO)
BioTop is a top-domain ontology for biomedicine,
represented in OWL-DL. It provides a class and a relation
hierarchy, together with description logics axioms
Analyzing the Categorial Structure in the light of description-logics based upper ontologies we find so many parallelisms that the hypothesis is allowed that the Categorial Structure can be interpreted, by and large, in terms of description logics axioms.
For instance, the basic categories can be declared as disjoint classes, e.g. Human Anatomy and Deed subclassOf Nothing (cf. (1) in section 2).
Semantic links in the model can be considered object properties with domain and range restrictions. E.g., has_means can be considered an OWL object property with its respective domain and range restrictions, according to (3.3): Thing subclassOf inverse (has_means) only Deed Thing subclassOf has_means only (Human anatomy or InterventionalEquipment or Lesion) Minimal constraints in the Categorial Structure model correspond to existential axioms, e.g. (3.1):
Deed subclassOf has_object some Thing or more complex (3.2):
Deed subclassOf ((has_object some HumanAnatomy) or
(has_site some HumanAnatomy))
One major difference between the Categorial Structure and
description logics is that OWL object properties are
exclusively relations between individuals (hence they require
quantifiers whenever used in axioms including classes),
whereas the links in the Categorial Structure hold between
classes. However, the links between classes can be defined
by means of the links between individuals in a similar way
as done in the context of RO
A rel B =def A subclassOf rel some B 3.4
Following the WHO Department of Patient Safety report on
a conceptual basis (a list of terms and definitions of patient
safety concepts3
The alignment method, however, remained the same for both tasks. First, we performed an analysis of the class definitions proposed in the ontologies (BFO and BioTop), where relevant classes were kept. Then a search for connections between these classes and PS-CAST was performed. Each alignment proposed was then reviewed by a Patient Safety expert. If class definitions were unclear or inaccurate, or if a relation was questionable, new proposals were made. The mapping was based on the OWL-DL versions of both ontologies. It used taxonomic subsumption (“is-a”) (A subclassOf B), and equivalence (A equivalentTo B).
The mappings were considered complete after a few iterations when no more changes were needed. We have ensured that no violation of domains and ranges were made. Table 1 is an excerpt of the two proposed mappings for PSCAST with BFO and with BioTop.
PS-CAST BFO (link type) BioTop (link type) Incident Process (subclass) Process (subclass) Incident_Type Disposition (subclass) Disposition (subclass) Circumstance Process OR Independent Condition (subclass)
Continuant (subclass)
lssseaCPCDeaertrseeoc_tnSioentting SPRirotoelec(e(sseusqbu(csilvuaasbslce)lnatssc)lass) ARMcoatliteoer(neiaq(sluuOibvbcajlleaecsntst)(csluabscs)lass)
Harm Process (subclass) Condition (subclass)
Anatomy Independant Continuant (StructuredBiologicalEntity OR
(subclass) ImmaterialObject) (subclass)
… … …
has_Cause - causedBy (equivalent relation)
itseerropPhhhhaaaassss____ILCMnooeccniaadsnteesinqotun_eTnycpee ---- (chphsaraauuossbLRscreeeoesslcaas(uluteiiszaqoal(unletiy)iqvo-auRnlieve(nlasatluetrbenerdtleaTrltaeiotolianot)ino)n)
… - …
As a general observation, the naming of several PS-CAST
classes suggests that these classes were defined rather by
functional than by ontological criteria. For instance, a
Circumstance is difficult to describe. E.g., a certain place can
be a circumstance of an adverse event just as an event or a
disposition. This ambiguity could be expressed by mapping
“PSCAST:Circumstance” to a disjunctive expression like
“bfo:Process or bfo:IndependentContinuant or
“bfo:Disposition”. In BioTop, such a disjunctive class is
already there, due to the need to represent ambiguous
clinical terms like “allergy” or “tumor”, for which different
readings (processual, material, dispositional) coexist
The World Health Organization (WHO) has initiated the
revision process of the International Classification of
Diseases4 (ICD-11) in 2007. Different from past revisions done
by WHO-FIC collaborating centres, the ICD-11 authoring
process, which involves a large community of clinical
experts, is supported by ontology-driven tools
the content model5
To try to disambiguate this blend of terminology and
information model a CAST approach was developed
The prerequisite was that diseases, disorders, injuries, signs and symptoms (all of which matter in ICD) cannot be attributed to one ontological category either.
The Ontology for General Medical Sciences (OGMS)
Three different CAST were proposed for Disease, Diagnosis and Patient Findings and Problems Disease is the most complete view. It is based on an abnormality in the Body System OR Structure (morphology) or in the Functional properties (patho-physiology), Causal properties and Manifestation Properties.
Disease/disorder furthermore has to be distinguished from Diagnosis, which represents the view of a clinical decision 5 www.who.int/classifications/icd/revision/contentmodel/en/index.html maker who shall take decisions in sometimes uncertain situations. Diagnoses are based on a set of Manifestation properties and Diagnostic criteria to be defined by the clinical domain-specific ICD-11 revision Topic Advisory Groups TAGs. Diagnoses principally include the possibility that they do not correspond to any pathological entity in the patient (suspected diagnoses or false diagnoses).
Finally Patient Findings and Problems (signs, symptoms, syndromes, test results, situations, etc.) are very often mentioned in health record for surveillance or other without reaching the level of a diagnosis assumption. 4.3
They are the relations has_finding, has_location, has_abnormality, has_etiology and has_focus. has_finding is the link authorised between Disease or
Diagnosis and Manifestation Properties. has_location is the link authorised between Disease or
Diagnosis and Body System/structure. has_abnormality is the link authorised between Disease and Functioning Properties or Body System/structure /Morphology. has_etiology is the link authorised between Disease or
Diagnosis and Causal Properties has_focus is the link authorised between Patient Findings and Problems and Manifestation Properties, BodySystem/structure, Functioning Properties. 4.4
Patient Findings and Problems: at least one has_focus. Diagnosis: at least one has_finding and at least one has_location Disease: at least one has_finding, at least one has_location, at least one has_abnormality and at least one has_etiology. 5
We presented the CAST approach on different healthcare sub domains (Surgical Procedures, Patient Safety, ICD 11) and the relations between this approach and ULO approaches (BFO and Bio Top).
We showed in a first step that CAST is challenging on one hand basic ontological entities and on the other the relations (Bio Top or BFO and RO).
In the following part we demonstrated that the use of the
CAST approach for the ICD-11 revision is facing the
ambiguity and fuzziness of the healthcare terminologies which
are oversimplifying the knowledge they contain to ease their
utilization. ICD 11 CAST blends ontology with information
model (and therefore epistemic) aspects, as in PS CAST.
Recently an ontological triad structure-named
structuredisposition process (SDP) has been proposed to
disambiguate complex pathological process in another healthcare
terminology SNOMED CT and the creation of a BioTop
disjunctive class recommended
The empirical nature of the CAST approach influences what should be represented - if some of these requirements are epistemic then the CAST should support them. If principled ontological frameworks cannot accommodate epistemic aspects this is not a reason to marginalize or reject them from the models (and associated knowledge products). The CAST, BFO and BioTop approaches are truly complementary. They are providing an empirical 'reality check' to quality improvement strategies that may disallow the inclusion of epistemic notions. They can support the process of ontology construction and ease ontology application when complex healthcare knowledge is concerned.
The crucial value in having computable models of these terminologies lies in the use of formal reasoning mechanisms for validation. Built into the workflow of terminology construction and maintenance, such a combined CAST ULO approach would be an important asset towards high-quality biomedical terminological systems.
PS-CAST project has been contracted by WHO (Registration #2009/33635-0, Order 200094768, Reg. File H15 APW 221) as part of ICPS development.