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Re: What databases have taught me

From: topmind <topmind_at_technologist.com>
Date: 25 Jun 2006 22:49:08 -0700
Message-ID: <1151300948.868683.76740@m73g2000cwd.googlegroups.com>

Neo wrote:
> > By the way, do any real-estate listings really track fridges?
>
> The andriod-based realtor that I am wiring in my garage, will :)
>
> > Most of your allegedly tough examples are based on physical modeling.
>
> If you mean't any modelling that that requires a table join or
> hierarchy, then there is some truth to that. In general, modelling
> hierarchies in RM cause some minor adjustments where as in dbd, it
> makes little difference if one is modelling a list, tree, table, or
> graph; they all require equally verbose scripts :) but the method
> remains largely unchanged.
>
> The tough part of dbd examples are the minimal impact to existing
> data/scripts/queries/code when meeting new data requirements unknown in
> advance (see example below).
>
> > > [Sample query to find first real-estate listing in dbd example 117]:
> > >
> > > (and (select single-family instance *)
> > > (select * has (and (select bedroom instance *)
> > > (select * has (and (select carpet instance *)
> > > (select * color purple)))))
> > > (select * has (and (select kitchen instance *)
> > > (select * has (and (select fridge instance *)
> > > (select * mfg sears))))))
> >
> > [RMDB's query]:
> > SELECT * FROM houses
> > WHERE houseType="single family"
> > AND houseID in
> > (SELECT houseID FROM rooms WHERE carpetColor="purple")
> > AND houseID in (SELECT houseID FROM furniture
> > WHERE furnitureType="fridge" AND brand="Sears")
> >
> > Note that I am assuming that the fridge can be anywhere in the house.
> > Adding kitchen-only would add another clause or join to the query.
>
> The above two queries are roughly equivalent (although the underlying
> data is structure is different, may need to add T_hasHierarchy). The
> most significant difference that is determinable from the queries is
> that in dbd's example, the fridge is located in the kitchen, where as
> in the RMDB example, the fridge is located in the house (which makes
> the RMDB query slightly simpler). Another signficant different that the
> fridge is a thing that could be move from one room to another or even
> one house to another without worrying about what
> attributes/subParts/contents belong to it.
>
> > People often put a 2nd fridge in their garage... I wonder how your query would look if the fridge could be in any room.
>

For the need it looks like you have in mind, perhaps it may make more sense to create a "meta" table(s) with dynamic attributes rather than a table for each kind of thing (furniture, rooms, etc). If a dynamic RDBMS existed in practice, such may not be necessary. But with the existing Oracle-copy-cat static-style RDBMS out there, skinny tables may be in order for your needs.

-T- Received on Mon Jun 26 2006 - 00:49:08 CDT

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