Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?
Date: Tue, 18 Feb 2003 20:17:46 -0500
Message-ID: <b2ulsp$10v$1_at_slb2.atl.mindspring.net>
Here are a few, including examples where <item, multiplicity> is a
natural conceptual model and where <item, item, item> is.
(also see my post previous to this, answering Bernard)
An inventory.
Ticket sales.
A receipt.
Groceries.
Perhaps I gave you the impression that I had something more
subtle in mind, but these are the kinds of things for which I think
multisets, sometimes conceived as sets of <item,multiplicity> pairs
and sometimes as true bags, are useful.
SK
When I inquire at a bookstore as to the availability
of a book, someone looks it up in a database and may report "we have
three in stock". If I purchase one, the physical implementation changes
"We sold 325 adult tickets and 104 child tickets today."
The tickets are separate physical entities, and when a family purchase
several, a machine issues several identical objects (they may well be
numbered, unfortunately), so this example is one where there is some
representation of the multiset as individual but identical items.
SQL Burger $3.29
Big Int $1.24
Table Service $.99
SQL Burger $3.29
SQL Burger $3.29
"Could I have two dozen jumbo shrimp, please?"
"and a dozen eggs?"
"and 5 pork and scallion buns?"
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>
>Steve,
>
>Could you provide a practical example that might help me in wrapping my mind
>around the notion of utility for logical models of items with
>multiplicities?
>
>I'm afraid I'm having problems understanding how one can even have some
>sense of determinancy of what constitutes a multiset in contrast to a set
>without some implicit logical mapping to identity. In the mind's eye, the
>very basis for contrasting a multiset from a set, or vice versa, is
>dependent on our very notion of identity.
>
>For example, if I see {1,1,1,1,1}, I would have a tendency to describe it as
>a collection of integer 1 values with a cardinality of five. In the process
>of synthesizing my description, I find that I implicitly assign cardinality
>to each member even though set theory would reduce this to {1}. Thus, I can
>distinguish between the two collections.
>
>What am I missing?
>
>I guess the root of my confusion lies in the fact that I don't see how we
>relate to anything in the real world without trying to apply some notion of
>identity in a logical sense.
>
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Received on Wed Feb 19 2003 - 02:17:46 CET