Re: Database design, Keys and some other things
Date: Sat, 01 Oct 2005 21:24:03 +0200
Message-ID: <433ee1b1$0$11077$e4fe514c_at_news.xs4all.nl>
paul c wrote:
> mAsterdam wrote:
>> Marshall Spight wrote: >> >>> We were discussing whether there was a difference between >>> the natures of external ids vs. surrogate keys. What is >>> essential to this question is what their nature is. Generally >>> we do not regard context-specific considerations as essential. >> >> It matters wether data come from the outside or >> from the inside of the system - the context of the data.
>
> If you say the answer to this matters, aren't you saying that the CWA
> doesn't matter? Doesn't the CWA give us a db all the context it needs?
To put this into perspective, here is a quote from: (http://metadata-standards.org/metadata-stds/Document-library/Documents-by-number/WG2-N0851-N0900/WG2-N0873-XMDR-Whitepaper-on-Ontologies-and-Formal-Statements-for-ISOIEC-11179-discussions.htm) Ontologies and Formal Statements for ISO/IEC 11179 Frank Olken, Kevin D. Keck, John L. McCarthy:
> H. Open World vs. Closed World Assumptions
>
> Ontologies, databases, etc. differ by what assumptions they make
> concerning whether the system is an open world or closed world
> (as described below). Given this diversity we need to specify for
> each ontology, etc. which assumption is operative. All ontologies
> and databases make some such assumptions.
>
> Closed worlds assume that the ontology/database encompasses the entire
> universe of discourse. Thus if a person is not in the personnel database
> then we may infer that he (or she) does not work for the organization.
> Closed World Assumptions (CWA) are nearly universal (unspoken assumption)
> in database systems.
>
> In contrast, most knowledge representation systems, e.g, ontologies, etc.,
> make an Open World Assumption (OWA), that the knowledgebase is presumed
> to be incomplete. Thus the absence of a particular fact from the
> knowledgebase does not permit the inference that the negation is
> true. This is very common in many scientific settings, in which
> the absence of a positive fact may simply indicate that no one
> has done a particular experiment.
When designing a database, we assume a closed world for the database under design. Aren't you sugessting we work within that same specific closed world when designing it? Received on Sat Oct 01 2005 - 21:24:03 CEST