Another distinctive feature of the conceptual model for
OLAP is its stress on aggregation of measures by one or
more dimensions as one of the key operations; e.g.,
computing and ranking the total sales by each county (or by
each year). Other popular operations include comparing two
measures (e.g., sales and budget) aggregated by the same
dimensions. Time is a dimension that is of particular
significance to decision support (e.g., trend analysis). Often,
it is desirable to have built-in knowledge of calendars and
other aspects of the time dimension.