Every NDS object has a schema class that has been defined for that type of object, and a class is a group of attributes organized in a meaningful way. Some of these attributes are mandatory and some are optional.
A mandatory attribute is one that must be completed when an object is being created. For instance, if a new user is being created using the User class, which has the employee number as a mandatory attribute, then the new User object cannot be created without providing the employee number.
An optional attribute is one that can be completed if desired but can be left without content. For instance, if a new User object is being created using the User class, which has Other names as an optional attribute, then the new User object can be created with or without data provided for that attribute--depending on whether the new user is known by other names. However, when an optional attribute is used for naming, the attribute then becomes mandatory.