Appendix C. Do Objects Persist or Happen over Time?

In their most spectacular change/innovation, KerML/SysML2 break with the established view (e.g., in UML) that objects are continuants, which persist over time, while events, actions/activities and processes are occurrences, which happen over time. For them, all things, including objects, are occurrences with temporal parts, which means that objects are identified with their histories/lifes. This new approach has far-reaching consequences, which don't seem to be well-understood yet.

In KerML/SysML2, objects are viewed as occurrences (or perdurants), so they happen over time by accumulating temporal parts, like processes, whereas in UML, objects are viewed as continuants (or endurants) that persist (and possibly change) over time while keeping their identity. The UML world view corresponds to a 3D ontology (referring to the three dimensions of the space, in which objects are extended), while the KerML/SysML2 world view corresponds to a 4D ontology, in which objects are extended in space and time.

We could ask the following questions:

Which of these two world views is more common sense?
Is one of these two world views philosophically (or scientifically) superior, and therefore preferable, or do both of them make sense similar to the wave theory and the corpuscular theory of light?
Is one of these two world views computationally superior, and therefore preferable?

Figure C-1. In KerML, both objects and their performances are occurrences.

The Common Sense View

Normally, we do not think that objects (such as my car or the Mount Everest) happen over time. Rather, we think that objects persist over time. And it's their history (or life) that happens over time, like other processes do as well.

So, we normally distinguish between an object and its history/life, not only in our common sense, but also in object-oriented modeling of information systems with UML.

But in KerML/SysML2, objects are identified with their histories, so they are considered to be occurrences, which are 4-dimensional entities, like processes, instead of 3-dimensional entities. Is this a good choice? What are its pros and cons?

Notice that in philosophy, this question (if objects are processes/occurrences) is an old debate, and there are both 3D Ontologies (such as DOLCE, BFO and UFO) and 4D Ontologies (such as BORO).

The Philosophical Debate

T.B.D.

What is computationally preferable?

Ed Seidewitz (in an LI comment): "for modeling temporal constraints, the 4D approach has a lot of formal advantages". Which ones?

T.B.D.

An Alternative To KerML's 4D Orthodoxy

Figure C-2. Allowing both 3D objects and 4D objects to co-exist.