Hi Tom > The reason HL7 doesn't do this is because the RMIM is already > dedicated to a particular topic, like lab observation or > whatever.
When you consider that an RMIM, a CMET and an HL7 graphical template are all basically the same thing, the granularity issue you mention doesn't apply. A single model can be used as any one of these [for those unfamiliar, an RMIM is a largish HL7 model, and a CMET is a smallish one, intended to be a component]. >The set of constraints in an archetype are constraints for representing content to do with > a particular topic, regardless of contextual use. Such as BP > measurement, diagnosis, etc. HL7 models can and commonly do have this level of granularity. What are generally called RMIMs perhaps typically don't, but a small "RMIM" model could be just such a BP measurement - a component in other words. It would generally be called a CMET or template but the model is exactly the same despite the name. These components are assembled into other models (which would perhaps be called full RMIMs, but could be other templates or CMETs), and this seems like the assembly of archetypes into openEHR templates. The larger model could correspond to a single report or business step just as with the openEHR template. (There is no UI aspect inherent to them, but nothing to stop a system rendering the model as an input screen.) >However, unlike in openEHR, an RMIM is a new schema, 'derived' from the RIM - but nevertheless a new > schema. This is obviously true to a degree since any HL7 model has a unique validation schema that checks that an instance or a fragment conforms. But all models are actually expressed in the single RIM schema, since even in instances, where you can have unique class names (eg ObservationSystolic, ObservationDiastolic) the RIM class is indicated via structural codes eg "classCode='OBS'". HL7 templates can be applied to these uniquely named classes even though the template has different class names (in fact normally the RMIM has the plainer names, and the graphical HL7 template the specialised ones). Templates are thus not tied to single RMIMs and so not to a single topic. cheers, Rik > -----Original Message----- > From: Thomas Beale [mailto:thomas.beale at oceaninformatics.com] > Sent: 09 December 2007 21:00 > To: rik.smithies at nhs.net > Cc: qamarr at cs.manchester.ac.uk; 'For openEHR technical discussions' > Subject: Re: openEHR and CEN models > > Rik Smithies wrote: > > Hi Tom, Rahil > > > > Templates are a neat way to foster re-use of R, because > they package > > up all the refinements and improvements you may want on R, but only > > those extra rules need be in the template - just the > differences. You > > don't put the rest of R in there. > > > this approach to representation is what is used by openEHR > archetypes and templates although in slightly different ways. > > Hence you don't need to keep cloning R over and over in order to > > re-use it with just slight variations. That would > proliferate objects > > and give you a maintenance headache. > > > But this only gives a basic level of re-use - reuse of the whole RMIM. > > As far as I'm aware there is no HL7 equivalent of openEHR templates > > (and I'm not sure there is an openEHR equivalent of what > HL7 calls templates either). > > An HL7 template is a "model of constraints" that goes along with > > another model. > > > > > well, that's what an archetype is, and a template is. But the > semantics are different. The set of constraints in an > archetype are constraints for representing content to do with > a particular topic, regardless of contextual use. Such as BP > measurement, diagnosis, etc. This provides a level of > definition where clinicians can define how to record all data > points to do with a particular subject, regardless of where > such data points might need to be recorded in the business process. > > OpenEHR templates provide a way to combine and further > constrain the data points expressed in archetypes, in chunks > or groups corresponding to context of use, i.e. screens, > reports or some other grouping that correspnds to a business > process step. There are many forms for example that will > capture vital signs, so you need a place to define all the > data points of the vital signs - the archetypes. > > The reason HL7 doesn't do this is because the RMIM is already > dedicated to a particular topic, like lab observation or > whatever. However, unlike in openEHR, an RMIM is a new > schema, 'derived' from the RIM - but nevertheless a new > schema. In HL7 speak, it is a data 'projection', i.e. > a selection of certain attributes from various classes in the > RIM, plus cloning. > > So HL7v3 is constructed as follows (simplifying the > DIM/RMIM/CMET business): > > 1 RIM -> N derived schemas (RMIMs) -> M templates per RMIM. > i.e N systems of 1 schema + M templates. > > openEHR is constructed as: > > 1 Reference Model -> N archetypes -> M templates, which are > N:N with archetypes (but more numerous). This gives a system > with a single schema > - the reference model - and 2 further levels of constraining > which allow topic-based deifnition and then context/business > event specific definition. But in the end all the information > is just instances of the reference model; in HL7, each > message (RMIM) has its own instances, because each is a > different schema. > > - thomas beale > > * > * > > ********************************************************************** This message may contain confidential and privileged information. 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