Re: Polygon data modelling question

Hi John, in your question, there are two alternatives. One is encoding each coord as a single column, the other is store them together as a text column. We have to consider the problem from the efficiency and extensibility.

From extensibility standing, the first method is better. Just think why DBMS first have to parse the SQL into a syntax tree, etc. This is because the decomposed things are more easily to handled in most cases. However, if you think no more functions of the project will be demanded, the second is also good.

From efficiency aspect, I can't easily give a conclusion. Because in the first method, there are many rows storing one spacical object, so if you use "update ... where id = obj_id" then: if row-level-lock is supported in dbms, this may be not a problem, if only page-level-lock is supported, this will cause performance degrade in frequent-update applications. For the second method, there is no problem like this since one row one object.

Method 1 and 2 don't have big gaps - they can be changed into each other. So don't worry too much about the design and initial implementation, both way are right in your case though I prefer the first one. Re-engineering can't be avoid since we can't predict the future.

(1) dbms are so different - know their performance by testing your plan on it;
(2) re-engineering can't be avoid;
(3) use simple way if you can't predict the future;

regards,

Qingqing

"John Palmer" <jopalmer_at_mail.vt.edu> wrote in message news:<a24amu$qd$1_at_solaris.cc.vt.edu>...
> Hi all,
>
> I have a question concerning a data model quandry I've gotten myself into.
> I need to store the absolute coordinates of pieces of wood as they exist in
> a truss, so that I can draw an entire truss. My original idea was to store
> pc_id, coord_id, xcoord, ycooord, zcoord for each coordinate for each piece
> in a table called pcs_coord. However, there is also the option of simply
> storing a comma delimited text-string in a single field and then pulling out
> that field's data and parsing it each time for to draw it. So my question
> is: what is the best way to do this? We won't be doing too much editing of
> the coordinates, if any, for now. We will be using these coordinates to
> generate pictures only for now. The only reason I like each coord as a row
> is that it makes it easier for me, in the future, to pull back these
> coordinates in an XML format like Scalable Vector Graphics without having to
> do parsing. Also, I can more easily find the max coordinates to do some
> scaling. But a co-worker says that if you never want to only return one
> row, ie one point, then it shouldn't be a row and that storing coordinates
> individually is a common mistake people make and we should learn from them.
> Does anyone have any ideas on what I should do?
>
> Thanks in advance,
> John Palmer
Received on Thu Jan 17 2002 - 16:17:24 CET