The focus in these rules is the design of displays and indexes in online catalogs. The focus here is not on the data structure, including the object of a record. It is intended that these rules could be used to design a catalog that consists of manifestation-based records (as in our current shared-cataloging environment), expression-based records, work-based records, or even a shared single virtual catalog that does not contain records at all in the conventional sense. Because these rules are data structure neutral, they can seem vague or ambiguous at times, especially when it comes to demonstrating relationships. Traditionally, we have demonstrated some relationships formally using citations and we have demonstrated other relationships informally using notes. An example of a formal demonstration of relationships: the fact that one work is based on another work is demonstrated by making a citation to the earlier work on all expression/manifestation records for the later work. Examples of informal demonstration of relationships: When one expression is based on another particular expression of the same work, a note is made to record the relationship between these two expressions of the same work. When one item is reproduced to create a new manifestation of the same expression of the same work, a reproduction note is made to record the details about which item was reproduced. It may be that we are moving into a world in which more universal machine-actionable identifers will be attached at the item, manifestation, and expression levels so that even these informal methods will eventually be transformed into formal linking using machine-actionable identifiers.
0.4 Record structure