Domain: A domain is a cohesive set of members. The set of members which comprise a domain share a certain common nature.

A domain is a set of [Member]s which relate to an [Axis]. A [Member] is always part of a domain of an [Axis], thus the term "member" means a member of the set of members (domain) for a specific [Axis]. Members of an [Axis] tend to be cohesive and share a certain common nature.

Domains have partitions. A partition is collectively exhaustive and mutually exclusive set of members within a domain. Partitions do not overlap. Given a set X, a partition is a division of X into non-overlapping and non-empty "parts" or "blocks" or "cells" that cover all of X. More formally, these "cells" are both collectively exhaustive and mutually exclusive with respect to the set being partitioned. Domains always have at least one partition and may have many partitions.