There is a 3-part structure of information within Stratum.Viewer that includes dimensions, hierarchies, and levels. Dimensions contain at least one hierarchy, which in turn contain at least one level, which in turn contain members. You can see an example of this structure in view explorer.
In this example, there is a Product Family hierarchy () with a Product Family level () in the rows for the grid. The hierarchy belongs to a Product Family dimension, which you can see when you access the Properties window for the hierarchy.
There are two time hierarchies in this example, and both belong to a Time dimension. The Year Months hierarchy () has Year () and Months () levels. The Year Weeks hierarchy () has Year () and Weeks () levels.