I was asked why rc_id in ISO13606 is mandatory, below is the summary for sharing.
Note: below few paragraphs are excerpt from ISO13606-1 2008 version spec.
ISO 13606 is not intended to specify the internal architecture or database design of EHR systems or components. Nor is it intended to prescribe the kinds of clinical application that might require or contribute EHR data in particular settings, domains or specialities. For this reason, the information model proposed here is called the EHR Extract, and might be used to define a message, an XML document or schema, or an object interface.
ISO 13606 may offer a practical and useful contribution to the design of EHR systems but will primarily be realised as a common set of external interfaces or messages built on otherwise heterogeneous clinical systems.
Now lets look at this RM (reference model) as shown below RECORD_COMPONENT class which is the top level class for most of the 13606 RM classes - COMPOSITION, SECTION, ENTRY, ITEM and ELEMENT. ELEMENT class is the object that really holds the actual data. (this is important concept, we will refer it later)
"rc_id" attribute inRECORD_COMPONENT class is mandatory, now let's look at the definition of this attribute in ISO13606 spec,
rc_id: The globally-unique identifier by which this node in the EHR hierarchy is referenced in the EHR system to which the data were first committed. This identifier shall be retained by the EHR Recipient and re-used whenever this RECORD_COMPONENT is subsequently included in
Below was my reply.
First, Is it meaningful or useful that every record in healthcare system has globally unique identifier in data exchange? As we mentioned above, RECORD_COMPONENT is top level class, so if rc_id is mandatory, then every sub class instance will need to supply value for rc_id.
Use a concrete example, lab test lipid panel has the following test item
Since in ISO13606 model, the actual data is holding in ELEMNT class, for the above test result, there are at least 4 ELEMENT object instance and 1 CLUSTER instance for the panel itself.
CLUSTER -- Lipid panel with direct LDL in Serum or Plasma
--> ELEMENT : Cholesterol [Mass/volume] in Serum or Plasma
--> ELEMENT : Triglyceride [Mass/volume] in Serum or Plasma
--> ELEMENT : Cholesterol in HDL [Mass/volume] in Serum or Plasma
--> ELEMENT : Cholesterol in LDL [Mass/volume] in Serum or Plasma by Direct assay
So for this particular report, the system needs to generate 5 GUID just to be compliant with the Reference Model. But how useful it is for data exchange? Does the receiving system need to know the GUID of each test item in the report? Will there be any value to the receiving system? Not at all.
Second, if the rc_id does not serve any purpose for data exchange, does it serve any purpose within the system? Yes, it is possibly required within the system itself, probably used as primary key to uniquely identify each record in database tables and the relationship. At relational data model level, there definitely needs to be primary key for each table, however this kind of information shall not surface at EHR extract reference model level. The abstract level information model shall not be mixed up the actual data model of the database otherwise each model will not be able to perform its intended function properly . Also it is contradictory to the intended objective of ISO13606 - "ISO 13606 is not intended to specify the internal architecture or database design of EHR systems or components".
So my conclusion is that it is wrong that ISO13606 RM specifies rc_id is mandatory.
However the user was not satisfied, he asked a very interesting question - why not let sending system specify what ever pseudo GUID in rc_id to be compliant with the reference model, and receiving system just ignore the value in rc_id, and then generate its own internally unique guid in rc_id attribute.
That's very very interesting - again back to the fundamental in any model design, if it does not serve any purpose, why you should model it in the first place?