Pipelined XPath Query Based on Cost Optimization

Algorithm 4

CreatePipeline (Ep, , T).

Input: XPath query expression Ep, XML statistics , number of available worker threads T.
Output: Pipeline represented by pipeline stage sequence .
(1)	← ExtractPrimitive(Ep);
(2)	← CostEstimate(, );
(3)	.size, ;//the number of primitives P; average cost of pipeline stage .
(4)	, ;//cost accumulation ; primitive sequence within a stage .
(5)	if ()
(6)	foreach primitive id
(7)	, ;
(8)	if ()
(9)	← CreatePipeStage(), ;
(10)	else
(11)	foreach primitive id
(12)	← CreatePipeStage(), ;
(13)	AdjustPipeStage();
(14)	return;