# Help:Property constraints portal/Contemporary

Two entities linked through a property with contemporary constraint (Q25796498) 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, uses (P2283), doctoral advisor (P184), conflict (P607), spouse (P26), etc.
2. Those describing the relative location. For instance, located in the administrative territorial entity (P131), country (P17), located in or next to body of water (P206), location (P276), 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 Using contemporary constraints to ensure data consistency (Q63983270).

## When are two entities contemporary?

Formally, two entities $e_{1}$  and $e_{2}$  are contemporary if, and only if, their life intervals intersect, ${\mathcal {I}}e_{1}\cap {\mathcal {I}}e_{2}\neq \emptyset$ .

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

The start time $e_{min}$  is the minimum acceptable value of all statements on $e$  using start properties date of birth (P569), inception (P571), start time (P580) or point in time (P585). Values with deprecated rank are ignored. If there are no valid statements using these properties, then $e_{min}=-\infty$ .

The end time $e_{max}$  is the maximum acceptable value of all statements on $e$  using end properties date of death (P570), dissolved, abolished or demolished date (P576), end time (P582) or point in time (P585). Values with deprecated rank are ignored. If there are no valid statements using these properties, then $e_{max}=+\infty$ .

In Boolean algebra (Q173183) and most programming languages, two entities $e_{1}$  and $e_{2}$  are contemporary if, and only if, $e_{1min}\leq e_{2max}\land e_{2min}\leq e_{1max}$ .

### Violation

When two entities $e_{1}$  and $e_{2}$  are not contemporary, ${\mathcal {I}}e_{1}\cap {\mathcal {I}}e_{2}=\emptyset$ , but are linked through a contemporary property, then there is a violation of the contemporary constraint (Q25796498).

## 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.