=========================
NXDL Data Types and Units
=========================

.. index::
    see: type; data type
    ! single: data type

.. _nxdl-types:
		
Data Types allowed in NXDL specifications
#########################################

Data types for use in NXDL
describe the expected type of data for a NeXus field or attribute. These terms are very
broad. More specific terms are used in actual NeXus data files that describe
size and array dimensions. In addition to the types in the following table, the
``NAPI`` type is defined when one wishes to permit a field
with any of these data types. The default type ``NX_CHAR`` is applied in cases 
where a field or attribute is defined in an NXDL specification without explicit assignment of a ``type``.

..  Generated from ../nxdlTypes.xsd via a custom Python tool
    ../../utils/types2rst.py ../../nxdlTypes.xsd > types.table

.. index::
   seealso: binary data; NX_BINARY

.. include:: types.table



.. index::
   ! single: unit category

.. _nxdl-units:

Unit Categories allowed in NXDL specifications
##############################################

Unit categories in NXDL specifications
describe the expected type of units for a NeXus field. They should describe
valid units consistent with the :ref:`NeXus units <Design-Units>` section.
The values for unit categories are restricted (by
an enumeration) to the table below.

.. admonition:: When no unit category applies...

    If a unit is not provided by the list of NeXus unit categories, instead
    of providing a category, a field element can include an example of the
    units directly.

    The example does not constrain the scale of the units. For example, if
    the unit is ``eV/mm``, the user could specify in a data file ``eV/cm``,
    or any other unit that is convertible to the example given.

    .. rubric:: Example
    .. code-block:: xml

        <field name="monochromator_dispersion" units="eV/mm">

    It is recommended that users and application developers check if their units
    and their unit examples adhere to the UDUNITS standard.  [#]_

    Conformance is not validated at this time.

    .. [#] https://www.unidata.ucar.edu/software/udunits/

..  Generated from ../nxdlTypes.xsd via a custom Python tool
    ../../utils/units2rst.py ../../nxdlTypes.xsd > units.table

.. include:: units.table