Widening BDDs

Boolean functions are often represented as binary decision diagrams (BDDs). BDDs are potentially of exponential size in the number of variables of the function. Boolean functions drawn from Pos (the class of positive Boolean functions) and Def (the class of definite Boolean functions) are often used to describe the groundness of, and grounding dependencies between, program variables in (constraint) logic programs. mypos-based analyses are often implemented using BDDs which are sometimes problematically large. Since the complexities of the most frequently used domain operations are quadratic in the size of the input BDDs, widening BDDs for space is also a widening for time, hence is important for scalability. Two algorithms for widening BDDs for space are presented and are discussed (with relation to groundness analysis).