[om-list] Re: Logical equivalence

[Mark Butler]

Luke wrote:

> Do you still envision storing primarily logical sentences (so as to use propositional or predicate calculus); vs. storing primarily the literal facts & observations they represent, together with the "original text" somehow attached as source material? 

Well, you are the one effectively in charge here, but I would say yes.
However, all of the statements simple enough to declare a discrete attribute
value for a discrete object should be accessible through an interface
virtually indistinguishable from a traditional database.  The difference comes
comes when accessing subtler and more contigent forms of knowledge, like "The
suspect was out-of-state when the crime was committed", which is a logical
constraint on the location of a person at a given time, not an exact value for
the location.

If so, and the logical statements are stored in an efficient way
(human-language names stored elsewhere in the system, so the logic is
compact/dense etc.), then what is the actual rubber-to-the-road difference
between  saying "object 123456 has a 543134 with value of 324" as a compact
logical statement vs. storing it in a database which is itself a compact
logical record of
> information? I hope that question makes sense.

The question makes perfect sense.  The answer is that for simple attribute
value assignments, there is no difference at all.  You can think of a
traditional meta model as allowing a certain limited class of statements about
object attribute values.  It is possible to work around that limitation by
going up a level of abtraction, but I beleive a better alternative is simply
to design the database to efficiently store statements of arbitrary complexity
in the first place.

The catch is that arbitrary statements are considerably harder for a query
engine to analyze, but I think that is a reasonable tradeoff given the
alternatives of either banning them completely or representing them in a way
inaccessable to the query engine itself.

- Mark