Variable values are stored in arrays. A variable's dimensionality refers to the number of dimensions and the dimension sizes of these arrays.
Each rVariable in a CDF has the same dimensionality. An array of values exists for each rVariable at each record in a CDF. The values may not be physically stored but may be virtual (see Sections 2.3.8, 2.3.10, and 2.3.11).
A zVariable may have a dimensionality which is different from that of the rVariables and the other zVariables. An array of values exists for each zVariable at each record in a CDF. As with rVariables the values may not be physically stored but may be virtual. zVariables are intended for use in those situations where using an rVariable would waste disk space or not logically make sense.
A variable array having two or more dimensions also contains subarrays. For instance, in a 3-dimensional array with dimension sizes [10,20,30], each array consists of ten 2-dimensional subarrays of size [20,30], and each of those 2-dimensional subarrays consists of twenty 1-dimensional subarrays of size [30]. Subarrays will be referred to when discussing other properties of CDF variables.