Re: ID field as logical address

From: Kevin Kirkpatrick <kvnkrkptrck_at_gmail.com>
Date: Mon, 1 Jun 2009 13:12:14 -0700 (PDT)
Message-ID: <a5076075-7ae9-4ab1-abf0-297ae601eb06_at_n21g2000vba.googlegroups.com>


On Jun 1, 2:27 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> "Kevin Kirkpatrick" <kvnkrkpt..._at_gmail.com> wrote in message
>
> news:895891d5-fe55-478d-81d7-e984bc37fff9_at_r13g2000vbr.googlegroups.com...
>
> > On Jun 1, 11:39 am, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> > > "Kevin Kirkpatrick" <kvnkrkpt..._at_gmail.com> wrote in message
>
> > >news:670a228b-b752-47eb-b2e4-68c966c449d9_at_s31g2000vbp.googlegroups.com...
>
> > > > What is the poor HR person to do when Mary Smith returns from a week
> > > > long Vegas trip and reports that she'd gotten married on Monday and
> > > > divorced on Friday?
>
> > > That should be obvious: issue two updates in succession, one for each
> > > event.
>
> > Am I reading that right?  You think the data entry person should
> > enter, as a fact to the database, "Mary Smith is currently Married",
> > at a time when Mary Smith is definitely not married?
>
> Yes, you're reading that right.  The data entry person should enter, as a
> fact into the database, "Mary Smith got Married", at a time when it is true
> that Mary Smith got Married, and then "Mary Smith got Divorced" at a time
> when it is true that Mary Smith got Divorced.

Sorry, I misinterpretted the relation {L, F, Stat} to indicate "The person with last name <L> and first name <F> is currently <Stat>"

It seems like you intended the relation to mean:

"The person with last name <L> and first name <F> got <Stat>"

But I'm still confused... at the time it was true that "Mary Smith got Divorced", and the database tuple changed from {"Smith", "Mary", "Married"} to {"Smith", "Mary", "Divorced"}, doesn't that imply that it was no longer true that "Mary Smith got Married"?

> The database has to be
> informed that a marriage occurred and then that a divorce occurred, since it
> is not just states that are being constrained, but changes of state.

"The database has to be informed that a marriage occurred"

I thought the UoD was limited to a person's current marital status (hence the single relation {L, F, Stat}). Is the fact that "a marriage occured" part of the UoD? If so, how is this fact represented in the data model? Received on Mon Jun 01 2009 - 22:12:14 CEST

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