Re: Entity and Identity

From: Roy Hann <specially_at_processed.almost.meat>
Date: Tue, 29 Sep 2009 07:05:44 -0500
Message-ID: <F7OdnbzbNpKFZVzXnZ2dnUVZ8kudnZ2d_at_pipex.net>



Clifford Heath wrote:

 Nilone wrote:
>> On Sep 29, 2:56 am, Clifford Heath <no.s..._at_please.net> wrote:
>>> I don't support multiple inheritance for value types
>> Why not?
>
> Because Object Role modeling does not. Neither does it support
> unrestricted MI for entity types. The logical reasoning behind
> what is allowed and what is not is contained in Terry Halpin's
> PhD thesis, where he grounded ORM as a FOL by proving the mapping
> to KL. If you wish you find a definition that extends MI in these
> cases, you're welcome to attempt it yourself, but for me, my
> training does not fit me to attempt it.
>
>>> and a value type cannot be derived from an entity type and vice versa.
>> Please explain the difference.
>
> A value type (aka lexical type) has a lexical form, or one which
> is commonly used to write its values. I can write a name or a
> phone number, but I cannot write a person or a telephone. In this
> sense, either a thing is, or is not, a value type; it cannot
> inherit both characteristics.

You've got me rolling in the aisle here. This is vintage stuff! Excellent. Are you here all week?

-- 
Roy
Received on Tue Sep 29 2009 - 07:05:44 CDT

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