Objects

Many HDF5 function calls use a combination of a location and name to identify an HDF5 object.

The location will be specified by a location identifier, loc_id, and will be an HDF5 file or object such as a group, dataset, or committed datatype*.

The name parameter, name, will be a character string and will specify the links to an object in an HDF5 file. The link or links to the object will be either an absolute path or a relative path. An absolute path will include all of the links from the root group to the object. A relative path will include all of the links from any other group to the object.

Several loc_id and name combinations are possible. To illustrate, the following combinations all identify dset3 in the file structure in the figure.

• If loc_id is a file identifier, name must specify the object from the file’s root group.

  loc_id specifies the file DATA_FILE1. 
  name = '/group2/group3/dset3'  

• If loc_id is a group identifier and the object of interest is a member of that group, name will simply be the name of the link to the object.

  loc_id specifies group3. 
  name = 'dset3'  

• If loc_id is a group identifier but the object of interest is not a direct member of that group, name would specify the object by a path relative to that group.

  loc_id specifies group2. 
  name = 'group3/dset3'

  Alternatively, name could specify the object with an absolute path in the file containing loc_id.

  loc_id specifies group2. 
  name = '/group2/group3/dset3'  

• There is one special case: if loc_id is the identifier of the object itself, name should be a dot ( . ). For those familiar with a UNIX shell, this works in much the same manner as a dot ( . ) specifying the current working directory.

  loc_id specifies dset3, the dataset itself. 
  name = '.'  

Many HDF5 functions accept loc_id and name in all of the above combinations. When accepted combinations are limited for a specific function, the limitations are mentioned in the function’s reference manual entry.

For a related discussion of the structure of HDF5 files and HDF5 path names, see “The Structure of an HDF5 File” (particularly the sub-section “HDF5 Path Names and Navigation”) in the “HDF5 Data Model and File Structure” chapter of the HDF5 User’s Guide.

* In the past, a committed datatype was known as a named datatype.