It seems that there are very few people involved in health information standards that are able to discern the difference between a thing in the singular and things in the plural! Perhaps many people can discern the difference but just don’t realize how difficult it is for computers to discern the difference. So often I see examples of scant regard for the critical differentiation of singular vs. plural in data specifications and clinical terminology.
Why is this such a problem? Well, the issue is fundamental to the design and implementation of clinical information systems and for intersystem communication. Whenever there are collections of items to be captured, stored, processed, communicated or displayed, the software engineer needs to ask herself: do these items represent the same type of concept or object? Can there be two or more identical objects of the same type? Is the order of the items important? The answer to these questions often changes the way a system is designed and implemented. If the software engineer needs to ask these questions, then the information modeller should do so too.
A list of medication orders is not the same as a single medication order. A vital sign is not the same concept as vital signs. In information systems and messages, these concepts need to be treated differently! The information structures need to be different. The operations on those structures need to be different.
The problem has really become dire where poor information specifications have been married to faulty terminologies by people who don’t seem to understand the implementation implications of these fundamental issues. Nowhere is this more evident than with recent HL7 CDA specifications, rushed out in the USA under the name of “meaningful use”. There is an almost anal obsession with “coding” and labelling every piece of data ( often the same data is coded/labelled multiple times!), to the extent that it appears more important to label and code the data item than it is to pay any attention to the actual meaning of the code or label or the actual meaning of the things being labelled, or the relationship to other data items, or to how easy or difficult it might be for every system that may need to parse the document in the future! In one HL7 CDA document I saw no fewer than 7! consecutive different labels/codes introducing the vital sign section of the document.
Now if a computer is trying to parse an HL7 CDA document and it is told that the next section is about “vital signs”, it would be handy to know that there is the possibility that there might be more than one vital sign – that we are referring to a collection of observations, associated with each other in some way. Yet if we turn to SNOMED CT for a code for vital signs, what do we find? We find a veritable chameleon, an hermaphrodite! A single and plural at the same time!
In SNOMED CT, the fully qualified name is “Vital sign (observable entity)”. The preferred term is “Vital signs”. There is also a synonym description “Vital sign”. Now if that is not having a bet each way, I don’t know what is. If we treat the concept as a singular, then SNOMED CT is rather nice, because it provides the specialisations of a vital sign for us, namely Blood pressure, Respiration rate, and Pulse rate. In this case, the 3 specialisations of a vital sign, also happen to correspond to the 3 constituents that make up the often accepted concept of the collection “Vital signs”. Unfortunately, we can’t rely on this in any generic way with SNOMED CT. It just happens to work for vital signs ( err, or did I mean vital sign? ).
It is also interesting to note that nearly all the recent HL7 CDA documents derived from the US Continuity of Care Record and Continuity of Care Document happen to have 4 vital signs, none of which is blood pressure. It seems so many people are blissfully unaware of the importance of actually getting the information modelling right! And that means right clinically, right computationally, and right semantically.
Until we get the fundamentals right, including differentiating singulars from plural, and understanding the fundamental nature of collections of things, in our terminologies and our information specifications, there seems little point in sharing clinical documents with the expectation that our computers can process the atomic data reliably, safely, or even just meaningfully.