We consider the requirements that a citation system must fulfill in order to cite structured and evolving data sets. Such a system must take into account variable granularity, context and the temporal dimension. We look at two examples and discuss the possible forms of citation to these data sets. We also describe a rule-based system that generates citations which fulfill these requirements. 1 Motivation Citations are one of the most significant tools used in the creation and propagation of knowledge; through citations we can give credit or attribution to researchers, convey a brief indication of the contents (such as a title), and provide location information for retrieval of the referenced work. Over the years, a well-developed system (with minor variations) has evolved for the citation of sources such as books, journals and scholarly papers. On the other hand, there is no well-defined mechanism for publishing, accessing and citing datasets [9, 1, 8]. Datasets are difficult to catal...