(24) Legal Reasoning with Situation Variable

We formalize a legal reasoning system based on situation-theoretic model, as an extended logic programming. In many aspects, legal reasoning depends upon such situations as scope of validity of codes, spatio-temporal locations, views, and so on. One way to formalize situatedness is to introduce the concept of module as a set of clauses into the language, however, modules are still clumsy to represent situations that should be composed, be decomposed, and change on the way of inference. Thus, we introduce situation variables that should be bound dynamically to the composition of particles of situations that are the primitives of situations in this system. In this project, we especially pay attention to the analysis of temporal reasoning, and we show the system that responds temporal situation for a certain event, as well as ordinary goal resolution. In the procedure of the unification of situation variables, we need to introduce the distinction of temporal features of eventualities; namely, we distinguish event/state/property for the term unification where the situation variables are bound differently according to these temporal types. The computer system based on this formalization is implemented in SICStus Prolog. We show an example of `excessive evacuation' in the legal domain as an application of our system.