Pipelined XPath Query Based on Cost Optimization

Algorithm 1

Preprocess (, ).

	Input: XML document , XPath query .
	Output: XML node region coding , relation index , XML statistics .
(1)	← Analyze();
(2)	id ← 0, level ← 0;//record the node ID and the level value of the current node
(3)	, ,;//initializing statistical variables
(4)	while(!EOF())
(5)	p ← Parsing();
(6)	if(p is StartElement)//when a header tag is encountered
(7)	u ← id,  ← CreateNewNode(p), , id ← id + 1, level ← level+1;
(8)	if( is EndElement)//when the tail tag is encountered
(9)	UpdateNode(.end);
(10)	if;
(11)	foreach node id
(12)	if;
(13)	if((.nodeType = ELEMENT)∧()∧(.level-1 = level))  = “/”;
(14)	else if((.nodeType = ELEMENT)∧())  = “//”;
(15)	else if((.nodeType = ATTRIBUTE)∧()∧(.level-1 = level))  = “@”;
(16)	if() ;
(17)	if((.level = .level-1)∧(.nodeType = ELEMENT)) ;
(18)	else if((.level ≠ .level-1)∧(.nodeType = ELEMENT)) ;
(19)	else if((.level = .level-1)∧(.nodeType = ATTRIBUTE)) ; ,
(20)	;
(21)	level ← level-1;
(22)	;//end while
(23)	, , ;
(24)	;
(25)	return {, , };