Automatic installation/local cache of definitions

[mkoennecke]

When you install cnxvalidate a copy of the definitions should be installed locally. With an option to update it from github.

Pete has code to do this.

[mkoennecke]

I wonder if this is a good idea. Especially, where in the file system hierarchy the NeXus definitions ought to live? As a stop gap measure, I added some text to the README which describes where to get the NeXus definitions from.

[prjemian]

IMO, it's a great benefit to the end user and also to the application developer. It provides a standard location and structure for different versions of the definitions. A tool might be created so that the end user does not have to reproduce the steps to correctly install a version of the definitions. A full clone of the repo provides too much information than is needed (manual, repo history) by a validation application. Validation needs the schema files and the NXDL files.

Every operating system today has a default location (for each username) to store files related to an application. The Python package appdirs describes this for various OS. In Linux, ~/.cache, ~/.config, and ~/.local (the XDG standard) are used, in slightly different contexts.

In C, I do not know if there is a system-indepndent library available to handle provide this location so it might need to be hard coded. I suggest (Linux) to create a directory ~/.config/cnxvalidate/ and storing various versions of the hierarchy within, along with any other files useful in managing this directory. An alternate might be ~/.config/nexus/ but that makes it less clear which application is in control of this content.