Dear Lisa, (01)
> Since data can change rapidly, does this mean that there is a
> separate model for each point in time? I can't tell. Is this
> supposed to be used in real applications? I can't tell.
>
That will depend on that nature of the data model. Many data models
are what I would call "current state" models. They are designed to
hold data that represents the current state of affairs, but if
things change, then changes are made to the data in the database,
and the previous state of affairs is lost. This sometimes has
severe consequences. (02)
I have spent a good deal of the last 20 years trying to persuade
people that it is relatively straight forward to avoid this
situation by using a data model that understands that things
change. This is one of the motivations for adopting a
4-dimensionalist approach to ontology (though it is not essential
to be able to track change over time). (03)
If you do this, then you clearly do not need a possible world for
each point in time, and you have the data to be able to determine
the state at any point in time. In these circumstances you only
need possible worlds when considering things like alternative
futures (plans) but each possible world would cover all times
of interest. (04)
Regards (05)
Matthew West
Reference Data Architecture and Standards Manager
Shell International Petroleum Company Limited
Registered in England and Wales
Registered number: 621148
Registered office: Shell Centre, London SE1 7NA, United Kingdom (06)
Tel: +44 20 7934 4490 Mobile: +44 7796 336538
Email: matthew.west@xxxxxxxxx
http://www.shell.com
http://www.matthew-west.org.uk/ (07)
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