schema(The set of definitions for the universe of objects that can be stored in a directory. For each object class, the schema defines which attributes an instance of the class must have, which additional attributes it can have, and which other object classes can be its parent object class)
Active Directory schema(The set of definitions of every object class that can be created in Active Directory, as well as the definitions of every attribute that can be assigned to that object class)
XML schema(The World Wide Web Consortium (W3C) standard language used for creating XML schema documents. The XML schema contains two parts: a set of predefined types (for example, string, dateTime, decimal), and an XML language for defining new types (for example, complexType, minOccurs, element))
