Re: Guessing?
Date: Mon, 07 Jul 2008 23:52:27 GMT
Message-ID: <%_xck.84951$gc5.52424_at_pd7urf2no>
Brian Selzer wrote:
...
> Consider the following statements:
>
> 1. Susan is an electrical engineer.
> 2. Susan is a mechanical engineer.
> 3. Susan is an electrical engineer or Susan is a mechanical engineer.
>
> Now, suppose you have a base relation P whose members map to individuals
> that exemplify the property of being an electrical engineer, a base relation
> Q whose members map to individuals that exemplify the property of being a
> mechanical engineer, and a virtual relation (a view) R (P UNION Q) whose
> members map to individuals that exemplify either the property of being an
> electrical engineer or the property of being a mechanical engineer or both.
> The presence of a tuple in the virtual relation with a value that maps to
> Susan tells us only that Susan exists and that she is either an electrical
> engineer or a mechanical engineer or both. It does not tell us which.