What is mean by APUPA pattern or arrangement?
Dr S.R.Ranganathan who is our father of Library and information science in India has enunciated a fundamental principle is known as APUPA pattern. APUPA pattern is one of the methods of arrangement of books in Classification. As per this method documents are classified in three types viz, Umbral, Penumbral and Alien. Umbral document implies the totally relevant document which is main interest of the reader. Penumbral document satisfies the marginal interest of the reader. This type is partially relevant and someway related to Umbral document. Alien document is totally non- relevant and thus is not required by the reader. So, we can recognize the pattern of every helpful sequence of book is Alien- Penumbral- Umbral- Penumbral- Alien - i.e. APUPA arrangement.
Thus the APUPA pattern arranges the most relevant book at the centre, books of marginal relevance on both side of the relevant book and totally disconnected books far away from the centre. This is the best way to maintain filiatory sequence. The filiatory sequence implies the placement of all the entities of a universe of knowledge in a definite sequence in one line according to the degree of their mutual affinities. The helpful sequence therefore, is said to be the one which follows the APUPA pattern.