what are the basic elements [of a theory] … each [theory] construct should belong to, or be derived from, one of the four archetype classes Actor, Technology, Activity and Software System. … What are the entities in terms of which a theory offers description, explanation, prediction or prescription? These are the constructs of a theory. Examples are “quarks” (quantum physics), “group process” (social science), “cognitive load” (cognitive psychology) and “programming skill” (SE). … (scientific realism) allow representations of hitherto unobserved entities (“gravity,” “quarks,” “feelings”) that are postulated to exist… In SE, the constructs would typically relate to people, organization, technology, activities and software system.

D. I. K. Sjøberg, T. Dybå, B. C. D. Anda, and J. E. Hannay, “Building Theories in Software Engineering,” in Guide to Advanced Empirical Software Engineering SE - 12, F. Shull, J. Singer, and D. K. Sjøberg, Eds. Springer London, 2008, pp. 312–336. [Springerlink]