Query Rewriting of FLWOR Expressions in XQuery
Lian Cheng-yang · Computer Technology and Development · 2009
The expression of FLWOR,whose rewriting has an important impact upon optimizing XQuery,is made up of clauses of For,Let,Where,Order By and Return.The previous research has focused on the expression of FLWR while lacking enough discussion on the clause of Order By.The clause is designed to sort the data in returned node-set.Besides,it is complicated and time-consuming to carry out this clause.Hence,divides the clause of Order By into three situations according to the inner and outer of For loop,then discusses them respectively.In addition,puts forward the method of rewriting the expression of FLWOR since the clause of Order By is combined with other clauses,which is intended to reduce the unnecessary repeated execution.The result of the experiment shows that the executing time after rewriting the clause always excels the previous one.