Earlier implementations of the query previews solutions ran into the problem of multi-valued attributes. Multi-valued attributes is a term used to define a situation where there are more than one value for a given attribute, for instance there are more than one actors in a movie. The first solution to this problem was to duplicate the entries for each instance of the multiple values. The next solution was applicable to situations where all the parameters were range variables and used Euler's formula was used to delete the replications. Euler's formula computes the number of datasets that actually fulfil a query by using a few simple arrays of data.
Temporal data is considered one-dimensional and has two arrays associated with it.
The first array specifies the counts of granules for each cell and the second array specifies the number of granules that cross over from one cell to the next. For instance the first array specifies the number of granules that have data for a cell say march 1979 and April 1979 and the next array specifies the number of granules that have data in both the months, march and April of 1979. If a user queries how many granules have data for the months of March and April of 1979, using Euler's formula the answer is the sum of all the granules per cell less the sum of the crossovers for all the granules. In the case of the geographic parameter, which is two dimensional, there are two more arrays corresponding to vertical crossovers and vertex of corner crossovers. The sum of the vertical edge arrays is subtracted from the net count and the sum of the vertex array is added back in.