ABSTRACT

We can describe the world, at any one time, as consisting of entities which may possess attributes, such as colour, spatial location, age, and so on. When we consider two times we find relationships between the entities at one time and those at another. For example, a piece of land may be divided into two, the two parts thus being related to the original one; a child is related to its parents; two entities at different times may be regarded as being “the same person”; what was once divided may coalesce into a single entity at a later time. These thoughts lead to a view of entities evolving over time which suggests the picture of Figure 1.