Based on dependence on content

• Content-independent metadata This type of metadata captures information that does not depend on the content of the document with which it is associated. Example of this type are location, modification-date of document and type-of-sensor used to record it. There is no information content captured by these metadata but they still be useful for retrieval of documents from their actual physical location.
• Content-dependent metadata This type of metadata depends on the content of the document it is associated with. Example of content dependent metadata are size of a document, max-colors, number of rows and columns in an image. Content-dependent metadata can be further sub-divided as follows:
  • Direct content-based metadata: This type metadata is based directly on the contents of a document. A popular example of this is full-text indices based on the text of the documents. Inverted tree and document [4] vectors are examples of this type of metadata.
  • Content descriptive metadata This type of metadata describes the content of document without direct utilization of those contents. This type of metadata often involves use of knowledge or human perception/cognition. An example of this type of metadata is textual annotations describing the contents of an image. This type of metadata come in two flavors
    1. Domain-independent metadata: These metadata capture information present in the document independent of the application or subject domain of information. Example of theses are the C/C++ parse trees and HTML document type definition.
    2. Domain-specific metadata: Metadata of this type is described in a manner specific to the application or subject domain of information. Example of such metadata are land-cover from GIS and population from Census domain. In case of structural data, the database schema is an example of such metadata. Another example is domain specific ontologies, terms from which may be used to construct metadata specific to domain.