AACR2 begins: ‘These rules are designed for use in the construction of catalogues and other lists in general libraries of all sizes.’ RDA offers: ‘RDA provides a set of guidelines and instructions on recording data to support resource discovery.’
The differences are instructive. AACR2 offers straightforward advice to librarians on constructing catalogues through the application of rules. Discretion is implicit in the word ‘rules’, which in common parlance are both broken and bent. But it also appeals to the enduring, imperishable, and magistral. Capitalized and collated with Saints and Popes the first rules defined the body of regulations observed by religious orders.
RDA is both more and less prescriptive, offering normative instruction – if you don’t follow instructions, things don’t work – and figurative lines to guide librarians. Its vocabulary is contemporary. As a linguistic device ‘resource discovery’ feels both unsatisfyingly vague and, in its sudden rise to prominence, destined for occlusion by a new memetic coinage. ‘Data’ is the oddest choice of all. Data are comprised of large numbers of small units of information, usually numeric, typically scientific. As a plural noun overwhelmingly used as a singular it is a word of uncommon dispute. Data are not naturally the stuff of bibliographical description.