Concepts and Applicability of Non-Functional Requirements for Particular and Universal Things

This paper discusses the main concepts and relationships for the Non-Functional Requirements (NFRs) domain ontology, which is placed at the top-domain level in the framework of a five-level ontological architecture. In this (ontological) context, the term Non-Functional Requirement (NFR) does not model a particular thing (concrete entity), but rather a quality-, constraint-related assertion of a certain aspect of the thing to be evaluated. Also, an NFR as a human assertion can deal with a thing category as a universal abstraction. Thus, the quality aspect attributed, for example, to a particular thing (as a class or its individuals) can refer to its parts, such as the properties and/or capabilities of the entity, or the entity as a whole. To better understand the concepts and relationships of NFRs, a basic background in the semantics of the foundational concepts such as Thing, Thing Category, and Assertion is needed. Furthermore, to validate the applicability of the ontological conceptualization of NFRs, a set of typical cases for different practical situations is showcased.