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Re: Stupid Database Tricks

From: Jan Hidders <hidders_at_gmail.com>
Date: Thu, 14 Jun 2007 07:23:43 -0700
Message-ID: <1181831023.432017.26430@j4g2000prf.googlegroups.com>


On 14 jun, 12:55, vldm10 <vld..._at_yahoo.com> wrote:

>

> Here I believe that you misunderstand what is key. I have
> 1. the identifier of the state of an entity or relationship
> 2. the identifier of the entity or relationship.
> I will use shortcut IdSt for first and IdEt for second
> Usually key is IdSt. But IdSt always goes in pair with IdEt.
> These two identifiers have strong semantic and conceptual base.

Could be, but they also might be complete nonsense. For the moment it is absolutely unclear to me what you mean by these terms. So how about you giving some proper definition and/or explanation of what they mean?

Let's, for simplicity, restrict ourselves to entities for the moment. I understand what it means if entities have certain attributes which have certain values. The state of an entity is usually defined as the total description of its attributes, i.e., a function that maps certain attribute names to their values. Such a state does not have an identifier, or even need one, since it identifies itself. So that raises the following questions:
- How do you define the state of an entity? - How do you define the identifier of the state of an entity? Ideally these definitions should be in terms of entities and their attributes. If you are going need other concepts then please define and explain them properly first.

The notion of identifier of an entity (in a certain entity set) is usually defined as a set of attribute names such that at no point in time there can be two entities in the entity set for which the values of the attributes in this set is the same. Are you using that defintion, or another one? If so, please define and explain it, also ideally in terms of entities and their attributes.

Let's restrict the discussion to this for the moment. Once this is cleared up there is the chance of proceeding in a meaningful way.

Received on Thu Jun 14 2007 - 09:23:43 CDT

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