The XDS interface class definitions are described in detail in XDS Class Definitions. The OM attribute types, syntax, and values and inheritance properties are described for each OM class.
A good way to begin to understand how the OM class hierarchy is structured and the relationship between OM classes and OM attributes to the service provided by the directory service package is to look up one of the OM classes listed in XDS Class Definitions.
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Example: The DS_C_FILTER Class