Attributes are ancillary data objects, normally of a limited size, associated with another object in the MINC 2.0 file. These attributes typically consist of either text or numeric data. In MINC, attributes are used to specify additional information about a variable or file.
MINC attributes can be considered to fall into three broad categories: Those which apply globally to the MINC file itself, those which play a structural role in defining the MINC file organization, and those which contain data or parameters associated with a specific group or data object.
Some string attributes are ``freeform'' and may contain any value without restrictions on format and length. Other string attributes are assumed to have a specific format. Still other string attributes must contain one of several well-known values. When this is the case, the well-known strings are padded with underscore characters to the length of the longest legal value. This convention was adopted to avoid restrictions imposed by NetCDF on increasing the lengths of existing attributes. Since this restriction is lifted in HDF5, future attributes need not follow this convention.
Numeric attributes may be in either integer or floating-point format. The MINC library provides attribute access routines which automatically convert a value to the desired type on retrieval.
HDF5 attributes may be attached to any group or dataset. In MINC 2.0, two attributes, history and title, are attached to the ``minc-2.0'' group. All other MINC attributes are local to a specific variable.