Objects that Can Dimension Variables

How variable and relation data is actually structured and stored is dependent on what type of object you use to dimension the variable or relation and the order in which those objects appear in the definition of the variable or relation Variables can be dimensioned by simple dimensions, concat dimensions, composites, partition templates, and alias dimensions. The object that by which you choose to dimension a variable determines how the data of the variable is stored.

Simple Dimensions

The members of a simple dimension are data values that all have the same data type. When a variable is dimensioned by a simple dimension, there is one cell in the variable for every member of the dimension. When there is a dimension member for which the variable has no data, Oracle OLAP stores NA values in the variable for that empty value. (Note that if storing these NA values would result in a full page of NA values that Oracle OLAP does not actually store the values.) Oracle OLAP does not store NA values when there is a range.)

Concat Dimensions

You define concat dimensions over previously-defined simple dimensions or conjoint dimensions. Consequently, the base dimensions of a concat dimension can be of different data types. You can represent a hierarchy with a concat dimension that is has two or more simple flat dimensions among its base dimensions. You can use concat dimensions to easily map dimensions in an analytic workspace to columns in relational tables and thereby promote more efficient loading of data from the relational structures into the analytic workspace structures.

Composites

You define composites over previously-defined dimensions or other composites. Conceptually, you can think of a composite consisting of two structures:

• The composite object itself. The composite contains the dimension-value combinations (that is, a composite tuples) that Oracle OLAP uses to determine the structure of any variables dimensioned by the composite.

• An index between the composite values and its base dimension values.

For a variable that is dimensioned by composite, Oracle OLAP does not create a cell for every value in the base dimensions as it would if the variable was dimensioned by a simple dimension. Instead, it creates array elements (that is, variable cells) only for those dimension values that are stored in the tuples of the composite; Data for the variable is stored in order, cell by cell, for each tuple in the composite. From the perspective of data storage, each combination of base dimension values in a composite is treated like the value of a regular dimension. This means that when you define a variable with one regular dimension and one composite, the data for the variable is stored as though it was a two-dimensional variable. Using composites to reduce the number of elements created for a variable results in more efficient data storage.

Partition Template

You define a partition template over previously-defined dimensions or composites. A partition template is a specification for the partitions of a partitioned variable. A partitioned variable is stored as multiple rows in the relational table of LOBs that is the analytic workspace—each partition is a row in the table.

Alias Dimension

An alias dimension is merely an alias for a simple dimension. An alias dimension has the same type and values as its base dimension. Typically, you define an alias dimension when you want to dimension a variable by the same dimension twice.