Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?

We don't have the same idea of what it means for a logical model to be useful, it seems. I define the utility of a logical model in terms of its relationship with a real-world model (it does a good job of logically representing the real-world model), and its relationship with a physical implementation (it admits a straightforward faithful physical implementation). Since I don't know what your definition of utility is, I don't know whether bags would clear the bar.

Steve

Bob Badour wrote:

>All of your multiset examples involve external physical representations.
>Why, then, are you suggesting a use for multisets as a logical
>representation?
>
>"Steve Kass" <skass_at_drew.edu> wrote in message
>news: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.
>>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
>>a "3" to a "2". It doesn't delete a fact from a table. Similarly, my
>>
>>
>local
>
>
>>pharmacy probably maintains an inventory of medications on hand. I
>>doubt that 1,237 tablets of alprazolam are represented by that many
>>entries in a database.
>>
>>Ticket sales.
>>"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.
>>
>>A receipt.
>>SQL Burger $3.29
>>Big Int $1.24
>>Table Service $.99
>>SQL Burger $3.29
>>SQL Burger $3.29
>>
>>Groceries.
>>"Could I have two dozen jumbo shrimp, please?"
>>"and a dozen eggs?"
>>"and 5 pork and scallion buns?"
>>
>>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
>>
>>
>>
>>>>
>>>>
>>>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.
>>>
>>>
>>>
>>>>>
>>>>>
>>>
>>>
>>>
>>>
>
>
>
>
Received on Wed Feb 19 2003 - 08:28:44 CET