When referring to classes and attributes in the directory service, the topics in Part 3 and Part 4 make a clear distinction between OM classes and directory classes, and between OM attributes and directory attributes. In both cases, the former is a construct of the closely associated Object Management interface, while the latter is a construct of the directory service to which XDS provides access. The terms object class and attribute indicate the directory constructs, while the phrases OM class and OM attribute indicate the Object Management constructs.