1. In a system that receives one or more expressions referencing data which is described by a hierarchical schema, wherein the one or more expressions comprise one or more components each of which may reference one or more branches of the hierarchical schema, a method of converting a single expression that references multiple branches within the hierarchical schema into multiple expressions that each reference a single branch of the hierarchical schema, the method comprising acts of: creating an empty list of new branches; for a particular base branch, parsing a component of the single expression to identify each branch with respect to the particular base branch that is referenced by the parsed component; and for each identified branch, adding a new branch to the list of new branches, wherein each new branch comprises an identified branch combined with the particular base branch.