Re: some information about anchor modeling

On 2012-07-19, vldm10 <vldm10_at_yahoo.com> wrote:

Suppose I am designing a database and I have decided (rightly or wrongly, but I _have_ decided) to use a surrogate key for a table whose rows are about some real-world object. We have to communicate with other people about these real-world objects, so we suggest it would be easier for all concerned if everyone used the same arbitrary numbers (i.e. our surrogate key) to refer to each particular real-world object. In fact, since we are a government department, we can tell them that they have to use it. Oh, we seem to have just invented something very like a VIN!

> The VIN is an intrinsic property.

No it is not. It is not even an acceptable candidate key. If you think that it is, consider a database about car crime and insurance fraud.

> A property is an intrinsic property of an entity if we can say: "yes,
> this entity has this property".

You forgot "and the property is permanent".

> Each attribute i.e. a particular value
> of a property, we determine by applying identification.

> For example, an adrress is not an intrinsic property of a person.

No, an address is not an intrinsic property of a person. It is not even an intrinsic property of a building.

> Note also that most entities are made by man.( Cars, buildings, credit
> cards, goods, invoices, etc )

Are you trying to say that whoever makes something can assign it an identifier? Of course they can, but that doesn't necessarily make it intrinsic; painting or tattooing a number on something does not make that number an intrinsic property of what would still be the same thing without the number.

Eric

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