Use of xsd:decimal instead of xsd:double for conversion factors

[jmkeil]

Using a comparison of unit ontologies with ABECTO I became aware that SWEET uses xsd:double to represent conversion factors and offsets. I think, instead xsd:decimal should be used, as binary floating point datatypes are not able to exactly represent many of the conversion values. Especially 0.1, 0.01, 0.001, … can not be represented. Only the lexical representation seems to be exact. However, the lexical to value mapping will map them to a slightly different value. This runs the risk of numerical problems in applications. I outlined this in detail in arXiv:2011.08077.

[dr-shorthair]

+1 from me.

I just made related PR in QUDT - qudt/qudt-public-repo#311
and OM is coming up behind HajoRijgersberg/OM#42

[lewismc]

@jmkeil thanks for registering the issue. Are you able to provide a pull request? If not, one of us can get around to it.