1. A document management method which uses a plurality of document schemas to manage a document retrieval request, the document schemas defining a structure of document contents, each document schema including a plurality of attributes, the method comprising the steps of: assigning a schema identifier to each of the plurality of document schemas by generating a global unique identifier value every time a schema name of a new document schema is input; and assigning an attribute identifier to each of the plurality of attributes of one of the plurality of document schemas by generating another global unique identifier value.