All valid operations involving an SDS can be done by calling routines in the SD interface. Except in rare instances, the physical file format used to store HDF data is transparent to HDF users.
The SD routines are described in the following table and in the HDF Reference Guide.
TABLE 3A SD Library Routines
The index describes the relative position of the data set in the file. The name is a unique character string and the reference number is a unique integer which are both assigned to the data set when it is created. The index, name, and reference number are needed to obtain a data set id.
The SDS id is the data set equivalent of a file identifier and uniquely identifies an SDS data set within a file. It is created when an existing SDS is selected for use or when a new SDS is created and is thereafter used to access the SDS.