HL7 and SNOMED CT - The Book

One long-standing complaint of this blog is the absence of clear, simple, explanatory, helpful and reliable literature on the HL7 RIM. It is thus a pleasure to note the appearance on-line of a pre-publication version of the new book by Tim Benson entitled Principles of Health Interoperability - HL7 and SNOMED, which is to be published in the Springer Health Informatics Series in November 2009. This is, I believe, the first book to provide extensive coverage of HL7 v3. (Mike Henderson's introduction to HL7 Messaging, with a practical focus, reaches only as far as v2.5.)

Benson's book is well-written and well-structured, and will provide a good starting point to those who are interested in the role of HL7 and SNOMED CT in current endeavors to realize interoperability in the realm of health information. Unfortunately in his treatment of HL7 RIM Benson still stays too close to the in many places confusing wording of the HL7 organization's own documents, and thus he does not provide the necessary level of clarity which would be needed for a more generally useful introduction to HL7 v3. In some cases there are outright contradictions, so that the reader is left with no reliable way of determining what is meant.

The problems at issue will by now be all too clear to the readers of this blog, but I will reiterate them nonetheless:

a. Confusing use of 'Act' to mean in some cases intentional action and in other cases anything that happens.

b. Confusing use of 'Act' (the same word) to mean in some cases a record and in other cases that which is recorded.

I provide passages to illustrate these problems below, confining myself to Benson's Chapter 7 – The HL7 V3 RIM, with one example taken from his Glossary. Emphases have been added by me. While the passages from ch. 7 are provided in their order of appearance, they are, inevitably, taken out of context. If someone can provide me with a key to the relevant context or contexts which will enable me to understand them consistently I would be more than grateful.

1. In his Glossary, Benson defines 'Act' as:

Any action of interest. Something that has happened or may happen.

(Interestingly, HL7 itself does not include the term 'Act' in its own Glossary, though it does include several of Act's children, and it presupposes an understanding of what 'Act' might mean in its definitions of the corresponding terms.)

The passages from Benson's chapter 7 are as follows:

2. "In HL7 V3, every happening is an Act, which is analogous to a verb in English. Each Act may have any number of Participations, which are Roles, played by Entities. These are analogous to nouns." [Act = any action of interest?, or any happening whatsoever (for example, a drug interaction, or an event in which someone dies as a result of a shooting accident)?]

3. "Act is a record of something that has happened or may happen. Full representation of an Act identifies the kind of act (what happens), the actor who performs the deed, and the objects or subjects (e.g. patients) that the act affects." [An Act is a record; an act affects patients; so 'Act' and 'act' are not synonymous; yet elsewhere in this chapter (for instance under 'Status Code') Benson uses 'Act' and 'act' interchangeably.]

4. "Information in a document is treated as an Act – the act being the creation of the document content." [Does this mean that information is the act of creating information? What, more generally, is HL7's view of the relationship between an Act, and what is treated as an Act? And is the act the record, or the creation of the record?]

5. "Each transaction is a kind of act." [I presume that this means that each transaction is an act (or Act?) of a certain kind.] "An account is a record of a set of transactions." [Does this, by 3., mean that an account is a record of a set of records?]

6. "Observation is defined as an Act of recognizing and noting information about the subject, and whose immediate and primary outcome (post‐condition) is new data about a subject. Observations often involve measurement or other elaborate methods of investigation, but may also be simply assertive statements, such as a diagnosis." [Are observations events of recognizing and noting? Or are they the results of events in the form of records or statements, as would be implied by 3. above and by the fact that Observation is a kind of Act? Or are they sometimes one and sometimes the other? Are some Observations records of Observations?]

7. "A Procedure is defined as an Act whose immediate and primary outcome (post‐condition) is the alteration of the physical condition of the subject." [Again, how can this be consistent with 3. above? How can a record alter the physical condition of its subject?]

8. "A particular Entity in a particular Role can participate in an Act in many ways. Thus, a person in the role of surgeon may participate in an act as primary surgeon or as assistant surgeon." [Is the surgeon participating then exclusively as record keeper, as is implied by 3. above, or also as surgeon?]

In summary, the RIM documentation creates for us a continuum of Acts, Events, Happenings, Recordings, and Records which are the Results of Recordings. It then posts different items to different points on this continuum on the basis of principles which seem unclear because the relevant distinctions between the different segments of this continuum are obfuscated in confusing ways.

Does this matter? Well, perhaps. There is currently much activity on the HL7 front in light of urgent efforts to bring about the needed interoperability between HL7 and the SNOMED CT vocabulary. How, under the conditions described above, will the Acts at the heart of HL7 v3 be callibrated in relation to what SNOMED calls 'procedures'?