1. A method of processing a performance query to a dimensionally-modeled fact collection by processing dimension coordinates that exist within a dimensional data model, wherein facts of the dimensionally-modeled fact collection are accessible according to the dimensional data model and wherein the dimension coordinates have a first particular grain (“finer grain”) that is finer than a second particular grain (“coarser grain”), the method to determine an evaluative score for a particular value at the finer grain (“finer grain value”) based on performance facts for dimension coordinates associated with the particular finer grain value, the method comprising: determining at least one performance parameter, relative to a particular value at the coarser grain (“coarser grain value”), against which to measure the performance facts associated with the finer grain value, including processing temporal relationships of finer grain values to coarser grain values for the dimension coordinates, wherein processing the temporal relationships of finer grain values to coarser grain values includes processing data indicative of how relationships of the finer grain values to coarser grain values change over time and, based thereon, processing performance facts based on performance facts for dimension coordinates having the particular coarser grain value; determining the evaluative score for the particular finer grain value based on performance facts of dimension coordinates having the particular finer grain value, in view of the at least one determined performance parameter; wherein processing the temporal relationships of finer grain values to coarser grain values includes performing one or both of unfettering and disambiguation to account for a changing relationship of grains so that the evaluative score is adjusted to provide a different type of evaluation score than a score based on a static relationship of grain values; said disambiguation comprising remapping the correspondence of fine-grained entities to coarser-grained entities when required to remove an ambiguity in how a fine grained entity maps to a coarser grained entity; and said unfettering comprising re-expressing the constraint in terms of finer-grained entities of dimension coordinates satisfying an original, coarser-grained constraint when required to account for a time changing relationship between finer grains and coarser grains.