XML support

NeXus files can grow quite complex it would be rather tedious to express the structure of such a file entirely in code. libpniio provides a way to create NeXus structures from XML. Like HDF5, XML structures data in a tree like hierarchy, making it the perfekt ASCII representation for a NeXus file.

Generating objects

The XML content can come from two sources

• a file

• or from a string.

Using the XML interface is rather simple. Consider that we have the structure of the file expressed as XML and stored in a file file_structure.xml using this is simply

hdf5::node::Group root_group = file.root();

nexus::xml::create_from_file(root_group,"file_structure.xml");

Alternatively you could use XML content from a string

hdf5::node::Group instrument = hdf5::node::get_node(root_group,"/entry/instrument");

std::string detector_struct = create_detector_structure();
nexus::xml::create_from_string(instrument,detector_struct);

As can be seen from this example the XML data must not contain the entire file structure. Instead it would be possible to provide separate XML files with different components of the file. Consider here for instance the following files

file	content description
basic_file.xml	the basic file structure
detector_1d.xml	structure for a 1d detector
detector_2d.xml	structure for a 2d detector

Code which uses this setup could look like this

hdf5::file::File file = ... ;
hdf5::node::Group root_group = file.root();

nexus::xml::create_from_file(root_group,"basic_file.xml");
hdf5::node::Group instrument = hdf5::node::get_node(root_group,"/entry/instrument");

switch(detector_setup)
{
   case DetectorType::LINEAR:
      nexus::xml::create_from_file(instrument,"detector_1d.xml");
      break;
   case DetectorType::AREA:
      nexus::xml::create_from_file(instrument,"detector_2d.xml");
}

It should be mentioned that currently libpniio does not use a validating parser which makes error detection rather difficult.

NeXus XML tags

Attention

Currently the entire content is described in the NeXus serialization documentation. Either need a link here or we have to provide a copy in this documentation.