Sentences in ASTL are constructed from terms in the language and can be constraints, grammar rules, or word entries. The complex term i-term is simply an infon pol where rel is a relation of arity n , is a term, and pol is either 0 or 1. The single colon indicates that S1 supports the situation type on its right-hand side. The supports relation in ASTL is global rather than situated. Consequently, query answering is independent of the situation in which the query is issued.
Constraints are actually backward-chaining constraints.
X are variables and S is a parameter. An interesting property of ASTL is that constraints are global. Thus, a new situation of the appropriate type need not have a constraint explicitly added to it. Grammar rules are another form of constraints.