Re: [h5md-user] Make "time" optional?

[Felix Höfling]

Am 16.07.2014, 13:20 Uhr, schrieb Pierre de Buyl <address@hidden>:

> > Concerning the versioning, we need an (internal) definition of what
> > "backwards compatiblity" means. As I indicated earlier, I suggest
> > something like
> >
> > "For y > x, the format version 1.y is backwards compatible to 1.x if a
> > reader expecting 1.y can deal with 1.x."
> >
> > An old reader expecting 1.x can not handle 1.y, of course. This means  
> > that
> > 1.y is a superset of 1.x, it may be more relaxed or include additional
> > fields.
>
> """The version x.y.z of the H5MD specification follows semantic  
> versioning
> (Preston-Werner): A change of the major version number x indicates
> backwards-incompatible changes to the file structure. A change of the  
> minor
> version number y indicates backwards-compatible changes to the file  
> structure."""
>
> If we make the proposed change, 1.0 readers will not be able to handle  
> 1.1
> files. If I understand well, this falls under "backwards-incompatible  
> changes to
> the file structure".
>
> P

Semantic versioning has basically been invented for software. If a future  
software version can process old input files, it is backwards compatible.  
In this sense, a file reader for the new file format processes old files  
as new ones (i.e., without extra hooks). However, there may be different  
interpretations in the context of a file format.

The interpretation that old readers must be able to handle new files  
drastically limits the possible "minor" changes to the file format, and is  
IMO useless. Translating to the software domain, it means that old  
software must be able to process future input files.

To make things more specific: making a previously mandatory field optional  
is backwards compatible. Changing the overall tree structure (or just  
renaming /particles → /atoms) is not.

Felix