Assignment of type is a fundamental operation in ontological work. ​

The terms "type" and "class" are used interchangeably by many ontologists. You identify classes/types for objects, then find their own classes/types for these classes/types, and you have basic types/classes in your top-level ontology. Each object of attention inevitably belongs to some type/class in the foundational ontology, for example, is either an object or a relationship.

It is quite important to understand for each object of attention which level of the model it belongs to, what type/class it has in the model of the next level, and so on. You assign types to objects when you identify them in the world, and you also try to assign types to objects that someone else has identified. Sometimes this is easy, sometimes not very, because it is not always possible to unambiguously do this from the context, and the type is not explicitly specified.

What are types used for in life? For ensuring a clearly defined reference and further for understanding which operations are allowed with an object, and which are not, in which relationships it can enter and in which it cannot. When the word "lives" stands alone, without constant use in a phrase, its type becomes unclear.

Usually, in the top-level ontology, only several basic types are defined, such as "class," "physical object," or "process" (note that the types of our top-level ontology will be provided below). At each level of the model, you can define by complete enumeration all possible types/classes, but usually this is done for the top-level ontology and for the meta-U-model, and for the meta-C-model, classes/types are added as needed in a more flexible way. This happens not because there is some sacred meaning in it, but because most people find it very inconvenient to create templates, it is easier to fill them. And the higher-level/abstract the template is, the more accurate it is.

There are several popular ontologies (ontological frameworks) that can be taken as a basis if you need to design something, and in general, you can orient yourself on them --- there is no need to invent basic types from scratch every time.

We use variations in the spirit of 4D extensional approaches of Chris Partridge^[1].

This is explained by their universality and simplicity: reliance on the spatial-temporal nature of reality, simple rules for sorting objects^[2], wide application in the industry^[3].