Reference bibliographies

The subject bibliographies which are mostly used for reference fall into this category. These bibliographies are considered to be exhaustive bibliographies. It is often quite impossible to compile absolutely exhaustive bibliographies, recording every single published document on any subject because so much of published material escapes legal deposit, advertisement, and the scattering of publications to books and journals is a problem which escapes the bibliographers vigilance. These types of publications therefore only aim to be exhaustive within chosen limits, which should be made clear by the bibliographers. Materials published in foreign languages are also a major limitation. 

The reference bibliographies can either be ad hoc, with occasional revisions or supplements or serial bibliographies with benefit of regular, at time frequent publication, and time saving cumulations. They also include indexing and abstracting services which are covered separately.