Several temporal references in natural language translate into more complex interval relationships than those listed in table 11.1. For example, ``same time'' frequently means that time intervals have to intersect, i.e. they have to share a certain range, ``during'' means that one interval has to be entirely included into the other one, ``exactly at the same time'' implies that the intervals must be the same. Such conditions can be implemented by composing several of the elementary ones. Table 11.2 gives a list of such conditions and also shows the way in which they have been composed of elementary ones. This information will be useful in section 11.3.2 when the calculation of join result sizes and join selectivities of these types of joins is composed of the results of the elementary ones.
| Join Name | 3c|Composition | Informal Description | ||
|---|---|---|---|---|
| equal join | = | same timestamps | ||
| overlap join | = | timestamps overlap but do not start or finish at the same point | ||
| contain join | = | timestamp of an  |
||
| contains the entire | ||||
timestamp of a  |
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| during join | = | timestamp of an is required to lie entirely within
the timestamp of a |
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| intersection join | = | timestamps intersect | ||