Defining attributes must always and necessarily be true about a concept.' For example, Scarlet fever necessarily has associated etiology Streptococcus group A ...
Representing Non-Defining Attributes in a Clinical Terminology to Support Practical Applications: Examples from SNOMED® Clinical Terms Marjorie C. Rallins, DPM,1 Kent A. Spackman, MD, PhD"'2 Jeff Wilcke, DVM, MS, DACVCP3 2Coliege of American Pathologists, Northfield, IL 2Oregon Health Sciences University, Portland, OR 3Virginia Polytechnic Institute and State University, Blacksburg, VA concepts that is useful for implementation but not always and necessarily true. An instance of information of this type is referred to as a "fact." This mechanism has been carried forward essentially unmodified from CTV3 into SNOMED CT.2 Facts are expressed as object-attribute-value triples in a table, where the value in each triple is drawn from the terminology. This permits hierarchical relationships among facts, but they are not inherited down the is-a hierarchy. Therefore, they are useful for expressing information about a concept that is not necessarily true about subtypes of the concept. Fact attributes are useful for representing information that may be different depending on location or country, or may change over time based on the decisions of a group of people, such as legislation. In addition to the example of "is-prescribable" given earlier, "reportable" is a fact attribute that specifies whether a disease is reportable to public health authorities in a particular realm.
SNOMED' Clinical Terms (SNOMED1 CT) is the combined work of SNOMEDO RT and Clinical Terms Version 3. The authors review the characteristics of SNOMED CT - defining attributes and non-defining attributes - which are vital in the development of practical applications
INTRODUCTION SNOMED CT is a reference terminology with a semantic network of explicitly defined concepts, and the functionality to employ non-defining attributes. Although defining attributes) have been a major focus of reference terminologies, we have discovered that non-defining attributes can be equally necessary to provide terminological support for clinical applications. DISCUSSION Defining attributes are those entities within the terminology that convey the meaning of concepts. Defining attributes must always and necessarily be true about a concept.' For example, Scarlet fever necessarily has associated etiology Streptococcus group A, consequently, "associated etiology" is a defining attribute. Defining attributes are semantically linked to other concepts within the terminology. These semantic links could be utilized for example, within a decision support application of online practice guidelines. By entering findings such as Streptococcus group A. that are specific to a particular patient, clinicians might be given recommendations tailored to that clinical situation.
CONCLUSION Clinical applications that are supported by controlled terminology require both defining and non-defining attributes. Even if the application is restricted to retrieval and analysis (functions that a reference terminology is designed to support) there is a need for the terminology to represent at least some nondefining characteristics of concepts. Through the incorporation of the "fact" mechanism from CTV3, the structure of SNOMED Clinical Terms provides more conprehensive support of practical clinical applications.
Non-defining attributes can be described as additional information about a concept that is included in the terminology but does not form part of the formal concept definition. For example, Valium may or may not be legally available for prescription ("prescribable") in a given country; consequently we sat that "is prescribable" is a non-defming attribute. There are instances where non-defining attributes are essential for implementing usable information systems. Clinical Terms Version 3 provides a mechanism for distributing information about
1067-5027/01/$5.00 C 2001 AMIA, Inc.
REFERENCES 1. Spackman KA, et al, eds. SNOMED RT Users Guide. College of American Pathologists, 2000. 2. SNOMED Clinical Terms Consultation Document: Core Structure. Version 19. Oct 2000. 3. Evans DA, Cimino JJ et al. Toward a medical concept representation language. JAMIA 1(3):207-217, 1994.
1006
