This property generalises the notions of "copy of" and "similar to" into a directed relationship, where the domain expresses the derivative, if such a direction can be established. Otherwise, the relationship is symmetric. If the reason for similarity is a sort of derivation process, i.e., that the creator has used or had in mind the form of a particular thing during the creation or production, this process should be explicitly modelled. Moreover it expresses similarity in cases that can be stated between two objects only, without historical knowledge about its reasons.

This property describes the use of material or immaterial things in a way essential to the performance or the outcome of an E7 Activity. This property typically applies to tools, instruments, moulds, raw materials and items embedded in a product. It implies that the presence of the object in question was a necessary condition for the action. For example, the activity of writing this text required the use of a computer. An immaterial thing can be used if at least one of its carriers is present. For example, the software tools on a computer. Another example is the use of a particular name by a particular group of people over some span to identify a thing, such as a settlement. In this case, the physical carriers of this name are at least the people understanding its use.