Whenever I hear the TMRM referred to or treated like a data model, I feel like saying in a Darth Vader type voice:
If the TMRM is a data model, then where are its data types?
It is my understanding that data models, legends in TMRM-speak, define data types on which they base declarations of equivalence (in terms of the subjects represented).
Being somewhat familiar with the text of the TMRM, or at least the current draft, I don’t see any declaration of data types in the TMRM.
Nor do I see any declarations of where the recursion of keys ends. Another important aspect of legends.
Nor do I see any declarations of equivalence (on the absent data types).
Yes, there is an abstraction of a path language, which would depend upon the data types and recursion through keys and values, but that is only an abstraction of a path language. It awaits declaration of data types, etc., in order to be an implementable path language.
There is a reason for the TMRM being written at that level of abstraction. To support any number of legends, written with any range of data types and choices with regard to the composition of those data types and subsequently the paths supported.
Any legend is going to make those choices and they are all equally valid if not all equally useful for some use cases. Every legend closes off some choices and opens up others.
For example, in bioinformatics, why would I want to do the subjectIdentifier/subjectLocator shuffle when I am concerned with standard identifiers for genes for example?
BTW, before anyone rushes out to write the legend syntax, realize that its writing results in subjects that could also be the targets of topic maps with suitable legends.
It is important that syntaxes be subjects, for a suitable legend, because syntaxes come and go out of fashion.
The need to merge subjects represented by those syntaxes, however, awaits only the next person with a brilliant insight.