I’ve written a new version of ‘Axioms of Versioning‘. I extended the formalization to get a grasp of the concept of ‘Semantic Backward Compatibility in HL7v3, which I believe is flawed (quote: “Objective of backward model compatibility is that a receiver expecting an ‘old’ version will not misinterpret content sent from a new version”). It seems to be the reverse of the position of the W3C TAG in ‘Extending and Versioning Languages: Terminology‘, and the position I would defend myself. Yet the interaction of new senders with old receivers was not sufficiently explored in my Axioms.

It turns out that exploration of this notion leads to quite natural definitions of ‘may ignore’ and ‘must understand’ semantics. The HL7v3 notion is probably best characterized by the concept of ‘partial semantical forward compatibility’ in my new Axioms. The concept is also close to, if not the same as, the TAG’s ‘Partial Understanding‘.

It really thrilled me to see how helpful my formalisms were in exploring the notions in HL7v3, and uncovering the – I think – hidden meaning in it.

From your note above

This would be very interesting, if my browser would show me the mathematical symbols in your discourse not as [] boxes, meaning the Unicode references couls not be resolved, but in the way you probably intended me to see them: as the mathematical symbols with which I established such a heartfelt love-hate relationship as an undergradute calculus student.

I considered printing the page and using it as a ‘fill-in-the-blanks’ exercise to remember those happy bygone days but reconsidered that it would probably be better to let bygones remain bygones ans post this comment.

Of course, that could be part of the problem-field as stated, because:

– I use a browser

– You use a browser

– But whoever will guarantee that we see the same things, e.g. is my

1. over the ages, the problem of reading back from a notation, be it mathematical or verbal, the same information that the auther poured into it, has as far as I know been formally stated but never been solved

2. however, each restatement of this same never-solved problem has

advanced our (humankind’s) knowledge somewhat

Bert Oldenburger:

“This would be very interesting, if my browser would show me the mathematical symbols in your discourse not as [] boxes…”

This is indeed – as you notice – a illustrating shortcoming in especially a note on a subject such as versioning. I used all HTML escapes such as ∃ for “there exists” (the reverse capital E) and ∀ for “for all” (upside down capital A), assuming this would ensure support among all browsers. Which version of which browser do you use?

It seems to be more a question of the right font.

For example the symbol ∈ ‘Element of’.

I have found

http://www.fileformat.info/info/unicode/char/2208/fontsupport.htm

The end of this tunnel is in sight but I don’t presently have enough time in my fueltank to see it through. A solution may follow &soonish;)