Slide 8 of 29
User defined time is some specific data type, or even a string, which is not interpreted by the t-GIS system and is thus not indexed. The application program may interpret it and then post-back a ‘proper’ time (usually a valid time).
Version changes are clearly transactions, but a full set of version services as provided by Laser-Scan or Smallworld is much more than just storing transaction times. They have higher-level time-like semantics usually with just precedences, e.g. Sandra updated the water class methods before David checked out the Caspian/Aral section to update the shorelines.
Version information, at a higher level than objects, is part of the schema and part of the metadata of a t-GIS.
Every version (in an eventual distributed system) could have its own clock which in principle could never be reliably synchronised: so you might need as many different types of time as you have places where people are updating distinct versions.
(A user can “check out” (semantically) a segment for version changes and then post back: either by extent (location) or by class (theme) or both.)
