Re: object algebra

> RDM has no internal format.

Per Date, RDM's fundamental representation unit, a relation, consists of 1) a heading of a fixed set of attributes 2) a body consisting of tuples (rows), each containing of values related to the heading. While the internal format doesn't prevent RDM (or any other model) from representing tables, trees, sentences, 4-D, etc, the internal format does have an impact on which structure are easier (tables) and which are more difficult (trees, Ex076). And in RDM's case, the internal format make it impossible to guarantee no NULLs will ever occur, unlike TDM which can make that guarantee.

> > XDb1 allows things of variable shapes to be entered via table, tree
> > and english-like sentences. For example, the following sentences
> > creates the equivalent of a relation with 2 tuples.
> > person isa thing.
> > john isa person.
> > mary isa person.
>
> So how is this better than a relation with 2 tuples?

Not much difference, if there are only a few (ultimately 1) tables in the db (ie T_Thing, T_SubVerbObj), however such an implementation is impractical in RDM. Received on Fri Feb 27 2004 - 03:16:10 CET