1. A computer-implemented method comprising: computing a query expression against a collection of XML documents stored in one or more tables of a database by, at least in part, executing a plurality of row sources of a query execution plan, said plurality of row sources including a path-based row source based on a path expression; wherein executing the path-based row source causes generating output rows based on the path expression operating on a set of input rows comprising XML data; and wherein generating said output rows includes filtering said output rows based on a row predicate condition that operates on at least one column of said output rows.