Re: [ontolog-forum] A minor point I noticed

[Simon Spero <sesuncedu@xxxxxxxxx>]

On Mon, Feb 11, 2013 at 2:37 PM, Pat Hayes <phayes@xxxxxxx> wrote:

But the history, of a conviction having been made and then quashed, remains and is indeed immutable. The apology may cancel the hurt of the tread, but it does not make the trodden foot retrospectively untrodden.

The Moving Finger writes; and, having writ,

Moves on: nor all thy Piety nor Wit,

Shall lure it back to cancel half a Line,

Nor all thy Tears wash out a Word of it.

"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 However, old facts can be superceded by new facts over time.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 

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.  

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.  

And doing a search for MVCC + Datomic, we find a comment thread on a video pitch for Datomic  where this point is made  http://news.ycombinator.com/item?id=4444793 .  (I haven't watched the video but 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.

Simon    

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