[NeXus-committee] obsolescence and evolution: NeXus needs a historic dimension

[Joachim Wuttke]

Pete:

> Perhaps you have been misinformed.
>
>>  From recent correspondence I learned that to this date not a single
>>  institute is writing fully valid NeXus.
>
> At one of the NIAC meetings in the last five years, we took an informal
> poll to discover which facilities use the NAPI to read/write NeXus data
> files.  "Less than half" was the result.  On testing data files for
> validity, many tested as valid.  I know of several instruments that have
> presented data files to me that have tested as valid against the current
> NXDL.  The software NeXpy now writes files based _solely_ on the
> structures specified in the NXDL.

Maybe I misunderstood or misremembered some communication, which
possibly was concerned more specifically with event-mode files.

Anyway, formal validity is perhaps a necessary, but certainly not a
sufficient condition for interoperability.

> This topic has been often discussed at NIAC meetings, generally during
> the deliberations over the request for a new feature.  Compatibility is
> one reason why major versions are not presented frequently.
>
>> has time come to start thinking
>> about a compatibility breaking next major version?

Maybe "next major version" is misleading wording for a leap like in
the Fortran example. It's certainly not to be done frequently.
I was rather thinking of a long time scale, and of a structured
process that starts with evaluating what has been achieved in the
past, what has been done right, what needs repair, and what is broken
beyond repair. If it is determined that the latter category is empty,
then the process can be stopped.

- Joachim

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