  The complexity of software-based systems has increased significantly,
especially with regards to capturing requirements along with dependencies among
requirements. A conceptual model is a way of thinking about and making sense of
the real world s complexities. In this paper, we focused on two approaches in
this context: (a) multiple models applied to the same system with simultaneous
usage of dissimilar notations vs. (b) a single model that utilizes a single
framework of notations. In the first approach, inconsistencies arise among
models that require a great deal of painstaking discipline and coordination
between them. The multiple-model notion is based on the claim that it is not
possible to present all application views in a single representation, so
diverse models are used, with each model representing a different view. This
article advocates a second approach that utilizes a single model with
multilevel (static/dynamic and behavioral) specification. To substantiate this
approach s feasibility, we embrace the occurrence-only model, which comprises
(a) Stoic ontology, (b) thinging machine (TM) language and (c) Lupascian logic.
In this paper, we focus on TM modeling as the mechanism of single-model
building. We claim that a TM can be a unifying diagrammatic language for
virtually all current modeling languages. To demonstrate such a claim, we
redraft almost all the diagrammatic representations in The Handbook of
Requirements Modeling of the International Requirements Engineering Board. This
redrafting includes context, class, activity, use case, data flow and state
diagrams. The results seem to indicate that there are no difficulties in
representing all views in TM.
