Re: Mixing OO and DB

On May 15, 2:51 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> TroyK wrote:
> > On May 14, 8:51 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>
> >>Bob Badour wrote:
>
> >>>topmind wrote:
>
> >>>>Robert Martin wrote:
>
> >>>>>On 2008-03-09 01:02:47 -0600, Marshall <marshall.spi..._at_gmail.com> said:
>
> >>>>>>On Mar 8, 6:07 pm, Robert Martin <uncle..._at_objectmentor.com> wrote:
>
> >>>>>>>On 2008-03-06 15:37:56 -0600, topmind <topm..._at_technologist.com> said:
>
> >>>>>>>>>Each small group of classes becomes a little roll-your-own data
> >>>>>>>>>access
> >>>>>>>>>and manipulation scheme that is perfectly tuned for it's very
> >>>>>>>>>specific
> >>>>>>>>>purpose.
>
> >>>>>>>>Which is over-kill for the task-level.
>
> >>>>>>>Do you have proof that it's overkill?  Do you have any objective
> >>>>>>>measurements that it's overkill?  Or it is just your own opinion.  I
> >>>>>>>mean, if it works for you that's great, but don't force your own
> >>>>>>>opinions on everyone else  <grin>
>
> >>>>>>This is a fallacious argument. You're proposing extra effort without
> >>>>>>justification. The idea that, in the absence of evidence either way,
> >>>>>>topmind's proposal of not putting in that effort is on equal footing
> >>>>>>with yours doesn't hold. Extra effort requires justification. What
> >>>>>>you are saying is, "hey, we don't know if this work has any value
> >>>>>>or not, so doing it is just as justified as not doing it."
>
> >>>>>Go back to the root of the argument.  You'll see that the initial
> >>>>>premise is that the programmer organizes the data into a form that is
> >>>>>more convenient for him to get his computational job done.  So there
> >>>>>*is* justification.
>
> >>>>Depending on how "convenient" is measured.
>
> >>>>Note that the effort to wrap SQL in methods is only one of the issues
> >>>>against it.
>
> >>>>>>>It is very common for programmers to manipulate data into forms that
> >>>>>>>are particularly convenient for the application they are writing.
> >>>>>>>Databases are seldom in that form since (for one thing) they must
> >>>>>>>usually serve many different and competing applications.
>
> >>>>>>(I'm going to just label the above as bogus without justification.
> >>>>>>It's late and I'm lazy.)
>
> >>>>>That's fine.  Consider, for example, an algorithm that finds the
> >>>>>minimum spanning distance of a graph.  (e.g. cheapest network route, or
> >>>>>cheapest travel itinerary, etc).  The node and edges of the graph are
> >>>>>stored in database tables.
>
> >>>>>Shall we execute that algorithm by doing thousands of tiny queries as
> >>>>>we walk from node to node through the edges?  Or shall we query all the
> >>>>>nodes and edges in one gulp, arrange them into a graph of objects, and
> >>>>>walk through them that way?
>
> >>>It's interesting that the self-aggrandizing ignorant should mention
> >>>minimum spanning trees. Creating a generic procedure for calculating
> >>>minimum spanning trees in SqlServer is on my to-do list as I write.
>
> >>>If one studies the algorithms for minimum spanning trees, one quickly
> >>>sees the task involves no traversals whatsoever. In fact, one generally
> >>>creates the MST as a precursor to some sort of traversal, and the
> >>>algorithms themselves are specified in terms of sets, which makes them
> >>>ideal for implementing relationally.
>
> >>>At the moment, I lean toward Kruskal's algorithm. Mostly, I just don't
> >>>understand Chazelle's algorithm well enough, and I don't have the
> >>>patience to hunt down the remaining details. Plus, it is difficult to
> >>>tease out how Chazelle's approximations might interact with dynamic cost
> >>>functions.
>
> >>>The algorithm relies on a disjoint-set structure, which is just a tuple
> >>>really. One would start by initializing a set of these structures with
> >>>an element for each vertex. Hmmmm... a set of tuples... hmmmm... I
> >>>wonder what sort of variable I could use to hold a set of tuples... I
> >>>think I will use a relvar.
>
> >>>For a general solution we need to associate a cost with each edge.
> >>>Hmmmm... an edge and a cost... hmmmm... I think I will use a tuple for
> >>>each of those and a relvar for the entire set once again.
>
> >>>For the result, we need a set of edges. I think I will use a relvar for
> >>>that too.
>
> >>>Once we initialize these relvars, the algorithm is quite simple:
>
> >>>While our edge-cost relation has at least one tuple:
> >>>  Choose one of the edges with the minimum cost.
> >>>  Perform a disjoint-set union on the two vertexes joined by the edge.
> >>>  Insert the edge to the MST result relvar.
> >>>  Delete all edges from the edge-cost relvar
> >>>    where the disjoint-set find places them in the same set.
> >>>Done.
>
> >>>The general solution on my to-do list is a little more complicated
> >>>because the cost function can be dynamic. There has to be another step
> >>>in the loop to re-evaluate the costs for any edges where the cost might
> >>>change.
>
> >>>[topmind's somewhat less informed response snipped]
>
> >>The Delaunay Triangulation code was more complex (proper domain support,
> >>which SqlServer lacks, would have helped), but the Voronoi Tessellation
> >>code could be as easy as a view. Lloyd's algorithm for k-means
> >>clustering was rather straightforward in t-sql once I had the delaunay
> >>and voronoi code in place.
>
> >>My to-do list is now void of computational geometry stuff for the time
> >>being. Sigh.- Hide quoted text -
>
> >>- Show quoted text -
>
> > Bob;
>
> > Quick question - which version and edition of SQL Server are you
> > working with? Although not proper domain support as you note, the
> > ability to create user-defined functions using the integrated CLR of
> > SS2K5 may get you "close enough" to make for some fairly clean T-SQL
> > expressions. Is this the route you went?
>
> > I'm wikipeducating myself on the Dalaunay triangulation and related
> > topics right now. This is pretty fascinating stuff, and interestingly,
> > ties directly to some topics in a linear algebra class I'm currently
> > taking.
>
> > TroyK
>
> SQL Server 2K SP4
>
> I make heavy use of temporary tables and for some strange reason one can
> neither pass tables as parameters nor reference temporary tables from
> user-defined functions.- Hide quoted text -
>
> - Show quoted text -

SS2K8 (upcoming) introduces table-valued parameters. It must have been a difficult feature, because I know developers have been asking for them for a long time.

TroyK Received on Thu May 15 2008 - 23:06:48 CEST