[Nexus-developers] NeXus file conversions, NOBUGS

[Mark Koennecke]

High ay,

On Mon, 7 Oct 2002, Ray Osborn wrote:

> On 10/7/02 1:38 AM, "Mark Koennecke" <Mark.Koennecke at psi.ch> wrote:
> 
> >  - One thing we should urgently sort out at NOBUGS is the XML issue.
> >    People start to define XML file structures everywhere: Ray has
> >    defined one, Steve King has done a similar thing, Emanuel Farhi as
> >    well, there is the XML-file structure created by using the NCSA HDF-5
> >    to XML utility. Perhaps this one could be check for the link handling
> >    problem. I think we should agree on a standard NeXus-XML definition
> >    as soon as possible. Nobody has yet a large investment in XML
> >    software, this may not be the case by the time of the next NOBUGS
> >    meeting. 
> 
> Well, there is an XML file structure already defined - it is defined by
> <http://www.neutron.anl.gov/nexus/NeXus_metaformat.html> and is implemented
> in NXtoXML.  Since there has been no discussion about it since I announced
> it on the NeXus mailing list, it is the de facto NeXus standard.  I have a
> submitted a poster about it to NOBUGS, and we can discuss it at the NeXus
> break-out session.
> 
> Of course, it doesn't define what goes in the files for particular
> instruments.  That is, I presume, the subject of Steve King's and several
> other people's NOBUGS contributions (I don't know about Farhi).
> 

  No, they have defined own versions of this mappings on their own.

> I don't think that there are many ways to map NeXus files to XML so it
> shouldn't be controversial.  Group classes have to become the keywords, with
> the group names as attributes, and we need to define a data type attribute
> that is not really a NeXus attribute.  Apart from that, the mapping is
> obvious, apart from the linking issue.
> 
  I do not think it will be controversial but we should seek some sort of
  general agreement before we make it a standard.

> > -  I believe now that it becomes unavoidable to extend the NeXus-API to
> >    deal with XML-files as well. Forward to version 3.0! XML would also
> >    address many peoples wish to have ASCII data files for easier
> >    manipulation. 
> 
> If you run NXtoXML, you can realize people's dreams today.  Actually, I
> found it helpful to see the NeXus files in this form, and I've started to
> use it in the web documentation for illustrations, e.g. see
> <http://www.neutron.anl.gov/nexus/NeXus_structure.html#Data>.
> 
   Writing XML is the easy bit. Parsing it from a program is another
   matter. You need to decide upon a XML parser and to learn how to
   use it. This is the main reason why I think we should extend the
   NeXus-API. And on the writing side, the use of NAPI would ensure 
   standard compliance without people having to read our format
   definitions.  

> Mark, if you want to say something about instrument definitions in your
> talk, please do so, but please base it on the XML specifications on the
> NeXus web site.  This was announced to the mailing list several months ago
> and has been used on the web site for several months, so we should use it as
> the basis of future planning even if modifications are needed.  This will
> also be the main subject of discussion at the break-out session.
> 
   No problem, my main concern is that the instrument defintion process is
   restarted. I also agree that the XML format description is superior to
   the simple one we decided upon at the last NeXus meeting.

			Regards,

				Mark