Help:Property constraints portal/Contemporary

Two entities linked through a property with Template:Q must be contemporary, that is, must coexist at some point in history. Properties with this constraint are called contemporary properties.

There are two main categories of contemporary properties:

1. Those requiring use, synchronous communication or direct physical interaction. For instance, Template:P, Template:P, Template:P, Template:P, etc.
2. Those describing the relative location. For instance, Template:P, Template:P, Template:P, Template:P, etc.

If, for practical reasons, this constraint is used in other properties, then it should never be defined as mandatory and a list of exceptions should be managed.

The specification and analysis of the contemporary constraint is available in Template:Q.

When are two entities contemporary?

Formally, two entities $e_1$ and $e_2$ are contemporary if, and only if, their life intervals intersect, $ℐe_1\cap ℐe_2\ne \mathrm{\varnothing }$.

The life interval $ℐe$ of an entity $e$ is the closed interval bounded by its start time and its end time, $ℐe=[e_{min},e_{max}]$.

The start time $e_{min}$ is the minimum acceptable value of all statements on $e$ using start properties Template:P, Template:P, Template:P or Template:P. Values with deprecated rank are ignored. If there are no valid statements using these properties, then $e_{min}=-\mathrm{\infty }$.

The end time $e_{max}$ is the maximum acceptable value of all statements on $e$ using end properties Template:P, Template:P, Template:P or Template:P. Values with deprecated rank are ignored. If there are no valid statements using these properties, then $e_{max}=+\mathrm{\infty }$.

In Template:Q and most programming languages, two entities $e_1$ and $e_2$ are contemporary if, and only if, $e_{1min}\le e_{2max}\wedge e_{2min}\le e_{1max}$.

Violation

When two entities $e_1$ and $e_2$ are not contemporary, $ℐe_1\cap ℐe_2=\mathrm{\varnothing }$, but are linked through a contemporary property, then there is a violation of the Template:Q.

Possible actions

There are several possible ways to address a violation of this constraint:

• Most likely, change or remove the statement that links $e_1$ and $e_2$ through the contemporary property.
• Fix the time value $min\{e_{1max},e_{2max}\}$. This value should be later.
• Fix the time value $max\{e_{1min},e_{2min}\}$. This value should be earlier.

Parameters

This constraint has no mandatory parameter.