Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

Hi,

"Jon Heggland" <heggland_at_idi.ntnu.no> wrote in message news:MPG.1d1cbf6e9c5f72ba98969c_at_news.ntnu.no...
> In article <42b185ff$1_at_news.fhg.de>, savinov_at_host.com says...
>> For example, consider the use of joins. We have several types of them
>> including manual joining by means of WHERE. Then in each individual
>> query you need to specify all the details of joins. Again, that is
>> needed because our database unable to derive necessary information. And
>> it is unable to do it because it does not know the semantics of data -
>
> Not at all. It knows constraints (of which foreign keys are an important
> special case), it knows domains. It can suggest "join paths", but if
> multiple paths are possible, some path (or combination of paths) must be
> selected! This can be done in multiple ways; *how* is not an issue of
> data model.

That's approximately what I wrote to AS awhile ago. He appears to be claiming that RM 'explicit joins' are the 'instructions' one has to specify in order to retrieve data and that the 'instructions', a.k.a 'explicit joins', are eliminated in his model.

>
> What makes your model "more semantic"? How does your model specify which
> path(s) to use? In your model, how does the EO, ED, EP, DM, OD database
> look, and how is the "find the offices of employees managed
> by Sally" handled?

For 'concept lattices' , or FCA, there was/is a navigation interface (TOSCAN ?) whereby one manually travels in a lattice (as one would in network model) selecting a path to arrive at a set of items. As far as I know, there is no query language for data retrieval in the FCA model although I maybe wrong on this.

Now, a more interesting question is what exacly AS's model is. It appears that it's different from concept lattices and I utterly failed to get a concise explanation from the author. Would you be able to explain the difference, by any chance ?

Thank you.

--
vc



> -- 

> Jon