extension of Clinical LOINC has been proposed as an nitial step in achieving this goal'2. Assuming sufficient ontological overlap exists between the concepts in ...
Expression of a Domain Ontology Model in Unified Modeling Language for the World Health Organization International Classification of Impairment, Disability, and Handicap, Version 2. Alexander P. Ruggieril2 M.D., Peter L. Elkin', M.D., Harold Solbrig', Christopher G. Chute', M.D. DrPH. ,
'Section of Medical Information Resources, Department of Health Sciences Research, 2Division of Rheumatology, Department of Medicine Mayo Foundation, Rochester MN 55905 The International Classification of Impairment,
be adopted by the World Health Assembly in May of 20013.
Disability, and Handicap Version 2(ICIDH-2), an anticipated addition to the World Health Organization suite of terminologies, has been put forth as a means for standardized representation of generic health and/or functional status data. In an attempt to make explicit the ontology upon which ICIDH-2 is based the authors derived a concept model expressed as a Unified Modeling Language static class diagram through abstraction of conceptterms in the documentation provided with the Full Version Pre-Final Draft of ICIDH-2 (December 2000). ICIDH-2's semantic structure is analyzed and evaluatedfor its semantic consistency. Discussion is presented on the utility ofdomain ontology models in terminology development and potential roles ICIDH2 might play, as it undergoes refinement towards a representational standard. It is intended that the proposed UML rendering will stimulate domain discourse and consensus that will lead to enhancement of conceptual clarity in the ICIDH-2 ontological hierarchy and further enable its study and development as a healthcare classification.
The introduction to ICIDH-2 states "a classification should be clear about what it classifies: its universe, its scope, it's unit of classification, its organization and how these elements are structured in terms of their relation to each other." In that spirit the documentation accompanying ICIDH-2 seeks to set forth, primarily through descriptive literary expression, the conceptual basis for the classification. While some visual modeling is employed to represent concepts and relationships, this is done in a form that is not syntactically controlled or precise.
The Unified Modeling Language is a standard modeling language maintained as a public domain standard under the Object Management Group4,s. Developed as a syntactically controlled notational language for specifying, visualizing, and documenting the artifacts of complex software systems, UML has been used to visually communicate concepts and relationships in systems in unambiguous syntactically precise ways.
Introduction
The current version of ICIDH-2 contains substantial documentation intended to describe the conceptual foundations of the classification. We sought to express this domain ontology using UML to build a static class diagram representing ICIDH-2 conceptual classes and relationships in a semantically explicit manner. Our goal is to clearly translate and the disambiguate conceptual foundations underpinning ICIDH-2 in order to promote its broad understanding and constructive analysis as a representational system for the functional status domain.
The International Classification of Impairment, Disability, and Handicap Version 21 (Pre-final Draft December 2000) was developed under the auspices of the World Health Organization. An expressed goal of the classification is the provision of a universal and standardized classification for the representation of data on human functioning and disability across an array of healthcare use cases. Published in its original version in 19802, ICIDH-2 represents revisions that have occurred since 1993. As such it is the only health terminology or classification devoted to general generic health or functional status domains. Developed in conjunction with a broad international panel of experts in this field, in its current version (ICIDH-2 Pre-final Draft Full Version) is expected to
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Figure 1. ICIDH-2 Domain Ontology UML Model; Human Function Package, Class Diagram. (Abstract classes are in italic) references within the ICIDH-2 document that were used in support of class derivations are indicated in the "Derivation" column in Table 1.
Methods The December 2000 Pre-final Draft of the WHO International Classification of Functioning, Disability and Handicap, Version 2, was downloaded in pdf format from the WHO Website6. The accompanying documentation was analyzed for terms representing concepts felt to be key or essential to the classification and its understanding. The criteria for designation as an ICIDH-2 key concept term were a textual demarcation in bold or italicized text and/or the provision of explicit definitions within the documentation. Classes were derived to build a UML class diagram model. Model Classes were either explicitly or implicitly derived. Model Classes that had a matching corresponding ICIDH-2 key concept term that had explicit definition were considered explicitly derived. Implicit Model Classes either had no direct matching key concept term, or had a matching key concept term which was not accompanied by an explicit definition expressed in the documentation. Implicit Model Classes were included only if regarded as essential to maintain model consistency, rigor, and clarity. A definition for each derived Model Class was posited that used the expressed ICIDH-2 definitions where possible, or with modifications to maintain logical consistency. Model diagrams were drawn using Microsoft Visio 2000TM
Our model for the ICIDH-2 ontology was expressed in two UML "packages" or domains that reflected our interpretation of classification occurring along two separate axes, "Human Function" and "Measurement" (Figures 1, and 2 respectively). The "Human Function Package" reflects concepts that constitute the ICIDH-2 view of the components of human "function". The other package, "Measurement Package", models the ICIDH-2 view of concepts involved in measurement or assignment of value or rating to a demonstrated instance ofhuman function.
Of the 24 Model Classes, 15 were explicitly derived from corresponding matching ICIDH-2 key concept terms. Not all ICIDH-2 key concept terms could be modeled precisely according to their literary definition. Some concept terms required interpretation beyond what was explicitly stated in ICIDH-2 in order to maintain logical consistency. As an example ICIDH-2 defines "activity" as the "execution of a task or action by an individual." However, based on the use of the term elsewhere in the classification we interpreted "activity" to be a rubric in ICIDH-2 intended to represent the concept of a task or action by and individual. The "execution" of an "activity" is a concrete instantiation and has concrete attributes such as the identity of the person performing the activity, time the activity was executed etc. ICIDH-2 "activities" as enumerated in the classification are terms or expressions representing "activity" concepts. In our model this conceptual class is represented by Activity. Similarly
Results
The modeling effort rendered a total of 24 Model Classes with features shown in Table 1. Specific page
575
Figure 2. ICIDH-2 Domains Ontology UML Model; Measurement Package, Class Diagram. (Abstract classes are in italic)
"Participation" defined in ICIDH-2 as "a person's involvement in a life situation" implies attributes describing a concrete instance and is inconsistent with the actual enumeration of Participation terms and expressions in the classification as abstract representations.
for simplicity and better understanding of the model. The remaining 3 implicit Model Classes not serving as generalization classes were derived from concepts felt importt and integrl to the classification but not explicitly described in the documentation. Among these was the Model Class Measurement, which we believe to represent a concept essential to articulating and understanding ICIDH-2.
Some ICIDH-2 terms, despite meeting the special textual demarcation criteria for a key concept term were not explicitly defined or were defined differently through the course of the documentation. Of the 18 Model Classes derived to represent ICIDH2 key concept terms, 3 (Construct, Performance Construct, and Capacity Construct) required implicit derivation of their definition despite having corresponding key concept terms within the documentation text. The Model Class Construct represents the corresponding ICIDH-2 key concept term "construct" highlighted and duly emphasized in Italics within the documentation. However, ICIDH-2 did not formally define this termL ICIDH-2 descriptions of the key concept terms 'Performance" and "Capacity" suggested each as a type of "construct", and from the context of the use of this term elsewhere in the documentation, a definition for the Model Class Construct was inferred. The Model Classes Performance Construct and Capacity Construct are modeled as subtypes of the generalization class Construct.
Discussion
Our intent in this paper was to express a model of the conceptual framework provided within the ICIDH-2 documentation in an explicit manner using a syntactically controlled modeling language. Our modeling effort should not be interpreted as an attempt at validation of ICIDH-2 concepts, the classification's utility, or its usability in the functional-status data representation domain in medicine. Domain experts involved as actors in functional status use cases must ultimately decide these attributes. Our model is intended only as a high level representation and does not ascnibe or describe the individual nomenclature elements or rubrics contained within ICIDH-2. Among the recognized quality indicators of controlled terminologies are non-ambiguous and nonredundant representations of concepts . Modeling is one way to attempt to make explicit concepts and conceptual relationships that underlie a formal terminology in an unambiguous manner. Models can serve as blueprints for firther distributed
Of the 6 remaining Model Classes requiring implicit derivation none had a corresponding key concept term. Of these, 3 were generalization classes derived
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development of a terminology and a mechanism for understanding how one terminology may interface with other controlled terminologies.
extension of Clinical LOINC has been proposed as an nitial step in achieving this goal'2. Assuming sufficient ontological overlap exists between the concepts in ICIDH-2 and those in functional status assessment instruments, ICIDH-2 might provide values for attributes or data elements within such structures. In order to achieve conceptual normalization among instrument items, reference to an ICIDH-2 code should be unique, especially if the ability to recall clinical data representing those concepts is sought. Whether concepts contained in a given instrument item can be uniquely, comprehensively, and thus usefully, represented by an ICIDH-2 rubric is a matter for further study. Success will depend on relative conceptual granularity between an ICIDH-2 rubric and the instrument item in question and on the degree of ambiguity and conceptual redundancy across ICIDH2 coded terms. Our hope is that the expression of a UML model on behalf of ICIDH-2 will initiate and enable a lifecycle of iterative refinement and distributed development of the classification.
The presence or absence of ambiguity in a classification or terminology is intuitive and difficult to measure or quantify. Our modeling effort rendered a number of classes derived implicitly from the ICIDH-2 documentation, and is susceptible to criticism that we misinterpreted the conceptual intent of the domain experts that created it. However, the number of implicit class derivations in our model may suggest a level of ambiguity inherent in the classification that its developers and interested users may wish to further address. Stimulation of clarifying discourse is a natural and fulfilling consequence of conceptual modeling efforts. The effort of ICIDH-2 developers to posit and articulate the ontology presumed by the classification, in and of itself, represents to us a distinguishing and notable feature. Building and expressing models of a domain ontology as a prelude to development of a terminology or classification to serve that domain might prove a fruitful way to facilitate and enable explicit creation of terminological content that is robust and semantically useful.
' International Classification of Functioning, Disability and Health, Pre-fmal Draft, Full Version, December 2000. http//www.who.int/icidh. 2Intemtional Classification of Impairments, Disabilities and Handicaps, 1980 World Health Organization, 1211 Geneva 27, Switzerland
3http://www.who.int/icidl/ebres/english.pdf 4Rumbaugh J. Jacobsson I, Booch G. The unified
UML modeling has been a useful tool in software engineering and analogously might serve the same purpose in terminology development. There is no particular advantage to use of UML to model the ICIDH-2 ontology other than it is a controlled specification and is used in other health inforniation standards development 8.
modeling language reference manual. The Addison Wesley object technology series 1999. Addison Wesley, reading, MA 5 http://www.omg.org/technology/uml/index.htm
6http://www.who.int/icidh
Data representation roles for ICIDH-2 can be projected through its further use and refinement. Use cases for functional status data representations are becoming increasingly prevalent in medical care. Functional status data structures are a significant part of the universe of information needing representation and indexing in the medical record. Functional status data obtained in patient care is often done through standardized "instruments" such as Short Form-36 (SF-36)9 and the Functional Independence Measure (FIM)10. These instruments include multiple items that often target specific aspects of human function. Many such instruments have been employed in general health services research and routine clinical care"1. A mechanism to normalize individual instrument items using standard representation could help achieve interoperability and comparability of data generated by their use. A semantic structure to represent instrument assessment items using an
7Standard specification of quality indicators for controlled health vocabularies, Elkin, P et al., ASTM / ANSI Standard (ASTM E20870) 8 Message Development Framework, Version 3.3, December 1999. Health Level Seven, Inc. Ann Arbor Michigan 9 Ware JE, Sherbourne CD. The MOS 26 item short health survey (SF-36) I Conceptual Framework and item selection. Med Care 1992 30; 473483 '0 Granger CV, Hamilton BB, Linacre JM et al. Perfonmace profiles of the functional independence measure Am J Phys Med Rehab 1993;72 84489 " Wolfe F, Pincus T, Data collection in the clinic. Rheum Dis Clin North Am 1995;21;321-58 12 Bakken S et al. Evaluation of the Clinical LOINC semantic structure as a terminology model for standardized assessment instruments. J Am Med Inform Assoc. 2000;7(6) 529-538
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