Dear all,
i have updated the temporal GIS algebra description in the trac wiki:
http://trac.osgeo.org/grass/wiki/Grass7/TemporalGISAlgebra
The update reflects weeks of discussion (including headache and twisted brains) with Thomas to create a working and usable temporal GIS algebra. We have introduced new spatio-temporal operators that allow an implicit time reference functionality.
I hope the update makes our approach and the goal of the temporal GIS algebra a bit clearer. In addition several examples are added for better understanding.
We would like to thank Edzer Pebesma and his research team from the Institute for Geoinformatics at the University of Münster in Germany for the very inspiring discussion and feedback about the temporal GIS algebra presentation that we made there. The idea of spatio-temporal operators was one result of our discussion in Münster. 
Best regards
Soeren