[Nexus] question about NeXus classes

[Akeroyd, FA (Freddie)]

> Today I discovered nxvalidate in the nexus trunk and tried running it
on some 
> of the test files in test/data. They either did not conform to the new
3.0 
> schema or the perhaps the schema does not include all the definitions
needed 
> to validate these files. nexus_defs/schema/testfile.xml does validate.
Is 
> there any additional information available concerning the new
organization of 
> NeXus classes/subclasses, new features, etc?
>   

Darren,

"nxvalidate" is a new tool that is not yet part of a standard NeXus
distribution. It has been developed as part of a project to move away
from Meta-DTD files for specifying base classes and instruments and to
instead use XML schema (see http://www.nexusformat.org/Schema for more
details). The NXtest.xml file generated by the testsuite when
napi_test-xml is run should validate with nxvalidate, but most NeXus
base classes have not yet been converted to schema so a general NeXus
file will not validate.

The "first pass" schema representation (3.0) will not change the current
NeXus definitions (2.0) structure and is intended to make validation of
current files more rigorous, but a few object oriented principles have
been used to make schema construction easier. For example classes that
represent instrument components each have "distance" and "NXgeometry"
members - to avoid duplication within the schema such classes will all
extend a new "component" abstract data type. These new types should,
however, not be used yet by other programs - eventually some of them may
become part of an official O-O NeXus API, but at the moment they are
liable to change.

Regards,

Freddie