rules at a lower level of abstraction from the technology than that aimed at herein.. I assume that my readers are familiar with the basic ideas of patterns and with the difference betweem a pattern catalogue and a pattern language. In particular, I have standardized on an `Alexandrian' format in the hope this this will also be familiar. Most of the patterns are presented as short `patlets' and some are summaries of patterns published elsewhere. 1 The RulePatterns language