HL7-v3-XML namespaces

Dear all,

I am currently studying the set of HL7-v3-XML messages.

What surprised me is that different of these messages (each of them defined by its own standard) all have the same namespace associated ("urn:hl7-org:v3").
So we find the same default namespace for the CCD/CDA, aECG and for the SPL standard - this though the root elements are really different:
- "ClinicalDocument" for CDA/CCD
- "Document" for SPL
- "AnnotatedECG" for aECG

So we find in the instance documents .e.g.:

CDA: <ClinicalDocument xmlns="urn:hl7-org:v3" ...
SPL: <Document xmlns="urn:hl7-org:v3" ...
aECG: <AnnotatedECG xmlns="urn:hl7-org:v3" 

I realize each of these three "standards" use a set of common elements and attributes, which are defined in schemas that are shared, but the main schema is different, and the composition (child elements) of the root elements is different each time.

Is this "good practice" or should have each of these "standards" essentially have their own namespace, and then have the common/shared elements in another, shared namespace ?

Your comments are appreciated.

Jozef

Jozef Aerts