Allen's interval algebra

The following 13 base relations capture the possible relations between two intervals.

Relation	Illustration	Interpretation
${\displaystyle X\,{\mathrel {\mathbf {<} }}\,Y}$  ${\displaystyle Y\,{\mathrel {\mathbf {>} }}\,X}$		X takes place before Y
${\displaystyle X\,{\mathrel {\mathbf {m} }}\,Y}$  ${\displaystyle Y\,{\mathrel {\mathbf {mi} }}\,X}$		X meets Y (i stands for inverse)
${\displaystyle X\,{\mathrel {\mathbf {o} }}\,Y}$  ${\displaystyle Y\,{\mathrel {\mathbf {oi} }}\,X}$		X overlaps with Y
${\displaystyle X\,{\mathrel {\mathbf {s} }}\,Y}$  ${\displaystyle Y\,{\mathrel {\mathbf {si} }}\,X}$		X starts Y
${\displaystyle X\,{\mathrel {\mathbf {d} }}\,Y}$  ${\displaystyle Y\,{\mathrel {\mathbf {di} }}\,X}$		X during Y
${\displaystyle X\,{\mathrel {\mathbf {f} }}\,Y}$  ${\displaystyle Y\,{\mathrel {\mathbf {fi} }}\,X}$		X finishes Y
${\displaystyle X\,{\mathrel {\mathbf {=} }}\,Y}$		X is equal to Y

Using this calculus, given facts can be formalized and then used for automatic reasoning. Relations between intervals are formalized as sets of base relations.

The sentence

During dinner, Peter reads the newspaper. Afterwards, he goes to bed.

is formalized in Allen's Interval Algebra as follows:

${\displaystyle {\mbox{newspaper }}\mathbf {\{\operatorname {d} \}} {\mbox{ dinner}}}$ 

${\displaystyle {\mbox{dinner }}\mathbf {\{\operatorname {<} \}} {\mbox{ bed}}}$ 

In general, the number of different relations between n intervals, starting with n = 0, is 1, 1, 13, 409, 23917, 2244361... OEIS A055203. The special case shown above is for n = 2.

For reasoning about the relations between temporal intervals, Allen's interval algebra provides a composition table. Given the relation between ${\displaystyle X}$  and ${\displaystyle Y}$  and the relation between ${\displaystyle Y}$  and ${\displaystyle Z}$ , the composition table allows for concluding about the relation between ${\displaystyle X}$  and ${\displaystyle Z}$ . Together with a converse operation, this turns Allen's interval algebra into a relation algebra.

For the example, one can infer ${\displaystyle {\mbox{newspaper }}\mathbf {\{\operatorname {<} ,\operatorname {m} \}} {\mbox{ bed}}}$ .

Allen's interval algebra can be used for the description of both temporal intervals and spatial configurations. For the latter use, the relations are interpreted as describing the relative position of spatial objects. This also works for three-dimensional objects by listing the relation for each coordinate separately.

The study of overlapping markup uses a similar algebra (see ^[1]). Its models have more variations depending on whether endpoints of document structures are permitted to be truly co-located, or merely [tangent].

• A simple java library implementing the concept of Allen's temporal relations and the path consistency algorithm
• Java library implementing Allen's Interval Algebra (incl. data and index structures, e.g., interval_tree)
• OWL-Time Time Ontology in OWL an OWL-2 DL ontology of temporal concepts, for describing the temporal properties of resources in the world or described in Web pages.
• GQR is a reasoner for Allen's interval algebra (and many others)

• Temporal logic
• Logic
• Region connection calculus.
• Spatial relation (analog)
• Commonsense reasoning

• Allen, James F. (26 November 1983). "Maintaining knowledge about temporal intervals" (PDF). Communications of the ACM. 26 (11): 832–843. CiteSeerX 10.1.1.472.5244. doi:10.1145/182.358434. ISSN 0001-0782.
• Nebel, Bernhard; Bürckert, Hans-Jürgen (1995). "Reasoning about Temporal Relations: A Maximal Tractable Subclass of Allen's Interval Algebra". Journal of the ACM. 42: 43–66. doi:10.1145/200836.200848.
• van Beek, Peter; Manchak, Dennis W. (1996). "The design and experimental analysis of algorithms for temporal reasoning" (PDF). Journal of Artificial Intelligence Research. 4 (1996): 1–18. arXiv:cs/9601101. Bibcode:1996cs........1101V. doi:10.1613/jair.232.