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(Related publication: [PUBLink])

The most prominent representative of explicit timeline representations is Allen's work on temporal intervals [PUBLink] [PUBLink]. Time intervals are the basic units, which are correlated by qualitative relations like BEFORE and OVERLAPS. A more efficient and flexible revision was presented by Freksa [PUBLink].

To represent quantitative information as well, metric information must be incorporated. Many planners with an explicit notion of time, e.g., zeno [PUBLink] and Descartes [PUBLink], use the approach of Malik and Binford [PUBLink], which employs linear inequalities to represent temporal (and spatial) information, and apply general constraint solvers. Other approaches use specific temporal management mechanisms, like the temporal constraint networks of Dechter, Meiri and Pearl [PUBLink] or the time map manager of Schrag, Boddy and Carciofini [PUBLink]. These are used in systems like HSTS [PUBLink].

An explicit timeline representation is a very general framework and does not specify how to express relations between actions, events and states. This extension is often made in combination with a logic language, e.g., Allen's interval temporal logic [PUBLink].

For the planning of EXCALIBUR's agents, the disjunctive feature of sequence-oriented representations is of little interest because of its combinatorial explosion. The temporal expressiveness of explicit timeline approaches, on the other hand, is much more important.

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Last update:
May 19, 2001 by Alexander Nareyek