A schema is a set of rules that governs the way that data can be stored in the directory. The schema defines the type of entries allowed, their attribute structure and the syntax of the attributes.
Data is stored in the directory using directory entries. An entry consists of an object class, which is required, and its attributes. Attributes can be either required or optional. The object class specifies the kind of information that the entry describes and defines the set of attributes it contains. Each attribute has one or more associated values. See Manage directory entries for additional information about how to manage entries.
For more information related to schema, see the following: