RE: Multi-layered Knowledge Representations for Healthcare (was RE: An argument for bridging information models and ontologies at the syntactic level)

 

	You are correct that classes in HL7 may have sub-classes. 
	[VK] I think the interesting question is whether these classes are
metaclasses, i.e., whether they belong to layer 1 or whether they are in layer
2.
	 
	 To be more specific, by definition, once a class in HL7 is
instantiated, the classCode and the moodCode can never be changed throughout the
lifecycle of the instance. 
	[VK] Was wondering if instead of having multiple class codes and mood
codes, if it were possible to actually represent them as individual classes?
	I beliebve the BRIDG model follows this approach.
	 
	 Therefore, operationally, the HL7 RIM ontology is definitively declared
when the instance is created. 
	[VK] This is interesting, because typically one first creates ontologies
and then instantiates them.
	 
	 Further granularity in the semantic meaning of the instance is declared
in the "code" attribute, which contains a series of fields: Original Text; 
	mapping of orginal text to an expression from a published vocabulary
(e.g. SNOMED); 
	[VK] If we view SNOMED as an ontology, this effectively declares that
instance to be an instance of the class described by the SNOMED expression.
	 
	 The essential rule of Term Info in HL7 is that none of these parts of
an "expression" may contradict the other, although each part may contribute to
the total semantic meaning of the "expression." It is also important that the
semantic meaning of the "class" within its hierarchy in the RIM and the meaning
of the published code within its hierarchy in the published coding system not
contradict each other. However, much work remains in order to remove
contradictions in the hierarchies of all these ontologies when used together.
	[VK] This is exactly where having a common representational formalism
and framework to represent information models and terminologies would be very
useful! 
	
	(As noted earlier, the RIM is a compromise between the very abstract,
raw, models like ASN.1 or EAV and the more concrete models often found in
database schemas for a narrow domain.)
	[VK] This sort of validates my opinion that it is more of a meta-model,
i.e., it belongs to Layer 1. 
	
	What are called Archetypes in OpenEHR correspond to HL7 structures
called Care Structures in HL7 Patient Care. These "Care Structures" represent
aggregations of classes used to represent a medical record construct such as a
problem list or care plan. Care Structures typical provide the "context" to very
granular concepts. For example, by itself, the term "diabetes Type 2" is merely
a concept. Once diabetes is placed within a problem list care structure for a
specific patient, the "sense" of  what is meant by "diabetes Type 2" in a
particular assertion of the term is more clear.
	[VK] Would be interested in undertanding the semantics underlying the
"Care Structure"? Maybe one could model specific classes for a Problem and a
Care Plan and may be Diabetes Type 2 can be a subclass or an instance of the
Problem MetaClass or Class. Just throwing out some alternate modeling approaches
..  Would like to know the fallacies if any. 
	
	In HL7 templated CDA documents (like CCD), templates are used to bind to
a schematron conformance test that validates that a certain XML Care Structures
(again, aggreations of classes, attributes, and vocabulary) do not extend beyond
a specific set of allowable constraints. Therefore, templates don't really add
to semantic meaning. However, the do enforce semantic meaning, and therefore
support improved interoperability.
	[VK] Agree CDA documents do not add to the semantics. We are more
interested in the information model or R-MIM underlying the CDA. 
	
	I hope this long-winded description helps in this "multi-layered
Knowledge Representation" discussion. How one classifies the concept of
"context" for a given concept, or the concept of "conformance testing the
constraints on an aggregation of structure and vocabulary" in a multi-layer
Knowledge Representation is not clear to me.
	
	[VK] Some thoghts on this are as follows:
	- A context can be typically represented as a MetaClass or a Class. 
	- A given concept can be a class which can be represented as an instance
or a sublcass of the context or associated with a context through well defined
	  semantic relationships
	- Can you present a concrete definition of conformance? I am assuming
for the purposes of this discussion Conformance = Semantic Subsumption.
	  Assuming that we have represented concepts and aggregation structures
in a common formalism, conformance would correspond to checking
	  for subsumption.
	 
	Obviously this needs to be further fleshed out and the best thing would
be to take a concrete example and work through the various issues you have
raised.
	 
	Look forward to feedback.
	 
	Thanks,
	 
	---Vipul


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