Maximising inheritance: Conform to BIDS 1.x

[Lestropie]

Extension of #2.

If it is possible for a data file to have any number of applicable metadata files at any level of the filesystem hierarchy, then the algorithm for determining the optimal placement of metadata fields in terms of filesystem level & entity set is relatively simple: each metadata value can simply be promoted up the hierarchy / have entities stripped as much as is possible.

However in BIDS 1.x, this is not actually permitted. For any given data file, there can be no more than one metadata file applicable at any given filesystem level.

Creating an algorithm that will both maximally exploit the Inheritance Principle, and obey this restriction, will I think actually be considerably more difficult than #2.

Here's one possibility:

• For each filesystem level (from highest to lowest):
  • Until there is no longer any opportunity to exploit inheritance at this filesystem level:
    • For every possible combination of entities:
      • Compute how many metadata field values could possibly be placed into that metadata file that would result in appropriate inheritance
    • Create metadata file with set of entities that resulted in the maximal number of metadata fields being placed within it

It's not necessary a globally optimal solution, but it might be adequate.