 in a Document Type Definition (DTD) or a schema document. [Computer and Information
Sciences] 
n., A group of related entities, or information about the entities, within a system arranged in a graded order, typic
ally from the most general to the most specific. [General Dictionaries] 
n.,n., A need to provide and receive explanation and understanding from one generation to another. Groups of individuals often derive their cohesiveness, legitimacy and the authority for their actions from their understanding