To press a suit means one thing to a tailor and another thing to a lawyer.
A free radical means one thing to a chemist but meant another thing to members of the House Un-American Activities Committee (HUAC) during the 1950’s.
And, medication for pain and pain medication don’t always mean the same thing. The controversy surrounding the recent death of Michael Jackson illustrates this last point.
In the examples above, as in clinical terminology, words can take on different meanings depending on factors like time or place (i.e., context).
Furthermore, clinicians and organizations use different clinical terms that mean the same thing. For example, the terms heart attack, myocardial infarction, and MI may mean the same thing to a cardiologist, but, to a computer, they are all different. There is a need to exchange clinical information consistently between different health care providers, care settings, researchers and others (semantic interoperability), and because medical information is recorded differently from place to place (on paper or electronically), a comprehensive, unified medical terminology system is needed as part of the information infrastructure.
Interoperability
Interoperability is the ability of two parties, either human or machine, to exchange data or information.
First, syntactic interoperability guarantees the exchange of the structure of the data, but carries no assurance that the meaning will be interpreted identically by all parties. Web pages built with HTML or XML are good examples of machine-to-machine syntactic interoperability because a properly structured page can be read by any machine with a Web browser. The meaning of the page to a particular machine may vary substantially; however, this is not usually considered a problem because the semantics of a page are meant to be interpreted by human viewers.
Next, human or semantic interoperability guarantees that the meaning of a structure is unambiguously exchanged between humans. Documents such as progress notes, referrals, consults, and others achieve semantic interoperability at a clinician-to-clinician level by relying on common medical vocabularies.
Finally, computable semantic interoperability requires that the meaning of data be unambiguously exchanged from machine to machine (as shown in the figure below). This does not necessarily mean that all machines need to process the received data the same way, but rather that each machine will make its processing decisions based on the same meaning.
Words and Meanings
The meanings of words change, sometimes rapidly. But a formal language such as used in an ontology -- a rigorous and exhaustive organization of some knowledge domain that is usually hierarchical and contains all the relevant entities and their relations -- can encode the meanings (semantics) of concepts in a form that does not change. In order to determine what is the meaning of a particular word (or term in a database, for example), it is necessary to label each fixed concept representation in an ontology with the word(s) or term(s) that may refer to that concept.
When multiple words refer to the same (fixed) concept, in language this is called synonymy; when one word is used to refer to more than one concept, that is called ambiguity. Ambiguity and synonymy are among the factors that make computer understanding of language very difficult. The use of words to refer to concepts (the meanings of the words used) is very sensitive to the context and the purpose of any use for many human-readable terms.
The use of ontologies in supporting semantic interoperability is to provide a fixed set of concepts whose meanings and relations are stable and can be agreed to by users. When a word used in some interoperability context changes its meaning, then to preserve interoperability it is necessary to change the pointer to the ontology element(s) that specifies the meaning of that word.
There are a number of tools for the programmatic handling (i.e., creating, querying, etc.) of ontologies. The visual representation of ontologies is an important contribution of these tools.
IBM Integrated ontology Development Toolkit (formerly named IBM Semantics Toolkit) is one of many toolkits designed for storage, manipulation, query, and inference of ontologies and corresponding instances.
An upcoming post will discuss the role and value of semantic technology in service-oriented architectures (SOA).
