On Decompositions of Chain Datalog Programs into \u3cem\u3eP\u3c/em\u3e (Left-)Linear 1-Rule Components

As an approach to optimization, this paper examines the decomposition of chain Datalog programs into P(left-)linear sequences of 1-rule programs. The notion of P (left-)linear, introduced here, encompasses numerous special (left-) linear forms and includes the traditional (left) linear as a subcase. The decompositions are first characterized in terms of properties of associated context-free languages. More specific characterizations are provided for three types of P (left-)linear decompositions with 1-rule components, and the corresponding decision problems considered. Finally, arbitrarily large, inherently nondecomposable, P-linear size-prime programs are exhibited