Pipelined XPath Query Based on Cost Optimization

Algorithm 2

PipedPrimitive (pName, , , tName, i, j, , , ).

	Input: primitive name pName, input unit data , blocking queue in following query primitive , tag name tName, input position index i, and output position index j in history record of unit data, region encoding , relation index , and global result .
	Output: none. The local results are processed in the algorithm: either put into the queue or output directly to the global result.
(1)	switch(pName)
(2)	case “GetDescendant”:
(3)	if(tName = “”) nodeTest ← true;
(4)	else nodeTest ← false;
(5)	;
(6)	foreach index
(7)	if((nodeTest = true ∨ .tagName = tName)∧(s.r = DE ∨ s.r = CH))
(8)	if()
(9)	; ←CreateUnit (, ); .enqueue ();
(10)	else;
(11)	return
(12)	case “FilterInput1byInput2”:
(13)	;
(14)	foreach index
(15)	if(()∧(s.r = DE ∨ s.r = CH))
(16)	if()
(17)	;  ← CreateUnit(, ); .enqueue();
(18)	else;
(19)	break;
(20)	return