[devdas]

Metrics. A metric has a known source, a timestamp, a name and a value. It can also ship with any arbitrary number of descriptive fields.

Similarly, events.

[geezerjay]

The known source might very well be expressed as a relation between two entities: a metric entity and a source entity.

The source entity, more often than not, is also complemented with other data that needs to remain a part of the persistence layer.