Classification of documents by information Characteristics:

The schemes of classification advocated by Hanson and Grogan are mainly based on the information characteristics of documents. Hanson divides documents into two categories -  primary and  secondary. Grogan  goes further and categorises them as primary, secondary and tertiary.

Primary Documents: 

These documents represent new knowledge or new interpretation of old knowledge. They are the first published records of original research and development. Often a primary document may be the only source of information in existence. According to Hanson,  books, journals, reports, patents, theses, trade literature, and  standards are the primary documents. Grogan adds to the list  conference proceedings and official publications, but excludes books. 

Secondary Documents:

Secondary documents do not carry new and original information  but guide users to primary documents. They are compiled from primary documents. They organise the primary literature in a convenient form. These documents are of three types: (a) Those which index selected portions of primary literature and help users in finding what has been published on a give subject, such as indexes, bibliographies, abstracts, etc. (b) Those which survey selected portions of the primary literature to help users find the state-of-the-art knowledge on a given subject, such as  reviews, treatises, etc. (c) Those documents which themselves contain the desired information collected and selected from primary documents. This information, such as biographies, facts, formulae, histories, procedures, theories, etc., is derived from primary documents  and is arranged systematically in some convenient  order in such secondary documents. Dictionaries, encyclopaedias, handbooks, manuals, etc., are some documents of this type. 

Tertiary Documents: 

Tertiary documents  list  secondary documents.  Their function is to help researchers in retrieving secondary sources. Directories, Yearbooks, Bibliographies of Bibliographies, Lists of Research-in-Progress projects, Guides to Literature, Guides  to Organizations, Guides  to Libraries, and Textbooks are included in this category of documents.