Re: Design question regarding data typing

On 24 Feb 2006 13:58:41 -0800, "Marshall Spight" <marshall.spight_at_gmail.com> wrote:

>Bob Hairgrove wrote:
>>
>> I still think we need to know what
>> purpose having the label "school" or "bank" will serve. Because as
>> soon as you need to have just one additional column from the
>> specialized table (i.e. schools or banks) in addition to the building
>> data, you will have to write a join -- and that makes your
>> building_type column instantly redundant.
>
>Having the subtype marker in the table for the common
>attributes constraints the entities to only participate in
>a single subtype.

How? What do you mean by "constraint" here? Please explain how this can be enforced (validated) at the engine level.

--
Bob Hairgrove
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