This article is about relational theory in physics. There is a separate article about the relational model.
In physics and philosophy, a relational theory is a framework to understand reality or a physical system in such a way that the position and other properties of the objects are only meaningful relatively to other objects. In a relational theory, space does not exist unless there are objects in it.
The alternative is an absolute theory in which the space exists independently of any objects that can be immersed in it.
Relational quantum mechanics is an interpretation of quantum theory which discards the notions of absolute state of a system, absolute value of its physical quantities, or absolute event.
Relational interpretations of quantum mechanics propose a solution to the interpretational difficulties of quantum theory based on the idea of weakening the notions of the state of a system, event, and the idea that a system, at a certain time, may just have a certain property.
Relational interpretations push this intuition further, by stating that, even when interacting, the position of the electron is only determined in relation to a certain observer, or to a certain quantum reference system, or similar.
The relational model depends on the law of excluded middle under which anything that is not true is false and anything that is not false is true; it also requires every tuple in a relation body to have a value for every attribute of that relation.
Usually in the relational model a database schema is said to consist of a set of relation names, the headers that are associated with these names and the constraints that should hold for every instance of the database schema.
A relation schema (H, C) consists of a header H and a predicate C(R) that is defined for all relations R with header H.
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