• Relative arrangement – where each book is labelled
according to the surrounding books, i.e. the book that
precedes and the book that follows, which is an approach
adopted by modern library practice since the 19th century
Book labels in a fixed arrangement are nowadays of interest
mainly to researchers in library history, especially late mediaeval
libraries and libraries from the 16th to 19th centuries. The system of
‘fixed’ call numbers, some of which can still be found in rare
collections, usually consisted of three elements: i) number of the
bookcase (possibly Roman numeral), ii) mark denoting the shelf
(possibly letter) iii) accession number (usually Arabic) a book
within that shelf.
It is relative shelf arrangement that is the standard
arrangement for modern libraries. Ranganathan stresses this when
defining a call number as a “number denoting the exact relative
position of a document in a library (relative to other documents and
not relative to shelves) and position of its entry in its catalogue”
(Ranganathan, 1967, pp. 519).
With the relative positioning of books, the following two
arrangements and two corresponding types of call numbering
systems coexist:
• Collection arrangement based on formal criteria only
(accession number, alphabetical ordering, chronological
ordering)
• Classified or systematically arranged collections, i.e. in
which the arrangement is primarily based on a books
content, followed by some formal arrangement within the
subject class