On Tue, February 12, 2013 17:12, Simon Spero wrote: (01)
> "A Datomic database stores a collection of facts. The facts in a database
> are immutable; once stored, they do not change. However, old facts can be
> superceded by new facts over time. The state of the database is a value
> defined by the set of facts in effect at a given moment in time."
> - http://docs.datomic.com/architecture.html (02)
> Looking at the datomic web site, it seems clear that they are using the
> term *fact *to denote grounded propositions which have been asserted in a
> database. It does not seem to be the case that these propositions need be
> have ever been true. (03)
I suggest that that is all that a logic-based system can do. It can not
go out and independently verify every assertion. Nor should we (imho)
desire it to do so. (04)
For testing, training, and other purposes, system designers often create
simulations on which to exercise their software. The data on which the
systems execute during simulations is not *true*. Reasoning and
processing should require that the data be consistent -- both internally
and with the appropriate models -- not that it be metaphysically true. (05)
> Looking at the documentation more closely, it seems that a Datomic
> *fact * is roughly equivalent to a version of a row in an MVCC DBMS,
> with the state of the database corresponding to a snapshot. (06)
Good. (07)
> ... reading the copy on the web site left me with the same feeling as the
> first poster - which is that the presentation of how DBMS's work doesn't
> apply to products from lesser known vendors like Oracle, PostgreSQL,
> MySQL, MS SQL Server, DB2 and so on. Well, and most of Sybase. (08)
Having data backup can be useful -- just as in software version control
systems. I can understand them portraying this as a benefit of their
system over the biggies. (09)
If they allow various types of archival reasoning, numerous opportunities
open up. (010)
-- doug f (011)
> Simon (012)
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