Low complexity aggregation in graphlog and Datalog [chapter]

Mariano P. Consens, Alberto O. Mendelzon
1990 Lecture Notes in Computer Science  
We present constructs for computing aggregate functions over sets of tuples and along paths in a database graph. We show how Datalog can be extended to compute a large class of queries with aggregates without incurring the large expense of a language with general set manipulation capabilities. In particular, we aim for queries that can be executed e ciently in parallel, using the class nc and its various subclasses as formal models of low parallel complexity. Our approach retains the standard
more » ... lational notion of relations as sets of tuples, not requiring the introduction of multisets. In the case where no rules are recursive, the language is exactly as expressive as Klug's rst order language with aggregates. We show that this class of non-recursive programs cannot express transitive closure (unless logspace=nlogspace), thus providing evidence for a widely believed but never proven folk result. We also study the expressive
doi:10.1007/3-540-53507-1_90 fatcat:2g6qdn6z6zdvzaenawkarx5rtq