In this section, the operation introduced in Section 3.2.1 is trivially generalized to collapse every path in a set of paths. Typically, first chooses a set of paths that match some regular expression, then the paths are collapsed, and a property is coalesced from the collapsed paths.
A set of paths, S, is collapsed by collapsing each path independently.
The utility of an operation like Collapse has been investigated in other semistructured query languages where it has been called ``pull-up'' . In Lorel, Collapse is not an operation at the query language level; rather, it is used in the implementation to compute the value of a path variable.