From: Austin Ziegler Date: 2007-03-29T13:13:04+09:00 Subject: Re: Object/Relational Mapping is the Vietnam of Computer Sci On 3/28/07, Daniel DeLorme wrote: > Austin Ziegler wrote: > > Sorry, Daniel, but you didn't show anything. You *claimed* that > > they're similar; you conflated things that have no relationship > > whatsoever. > It might be impudent of me but have you considered that just maybe *you* > are the one who can't *see* the relationship? But you are right I didn't > show anything. Just take any ORM layer and the fact that you can > directly and easily map a SQLDB to an object model is all the proof I > need that a RDBMS *can* indeed be expressed as an object graph and that > an OODB can therefore be relational. Wrong. This is completely backwards. The relational model can *certainly* model an object graph; an object graph is not thereby automatically relational. You're assuming that "a therefore b" also means "b therefore a" and that just ain't the case at all. Object databases aren't based on relational theory. They *pride* themselves on being so-called "post-relational"; in reality, they're not based on any viable theory. They're brute force applications of fads and prejudices. > > You're right that object graphs don't *have* to be hierarchical; > > object databases are uniformly so, though. > I have trouble believing that *all* of OODB implementers would be so > stupid as to implement a hierarchical-only structure. If that is indeed > the case then I can see that a being a complete waste of time. > > It's now clear to me that we are arguing about different things; you > about the (hierarchical) OODBs that you know and I about the > (relational) OODBs that I can imagine. In the end, I believe OO is more > about the physical model than the logical model of data. > > Darn semantics strike again! Object database proponents tend to believe that the relational theory is ... bunk. In return, they offer nothing that hasn't been tried before and shown wanting. > > I highly recommend you take > > the time it requires to study relational theory. I'm not a heavy > > practitioner myself, anymore -- I don't do stuff that needs databases > > right now. > Unfortunately my brain has a strong resistance to jargon-rich > litterature such as academic papers or legalese. :-( The basics of it aren't hard; it's set theory with relational algebra. I'm just not good enough at it to explain it nearly as well as some of the papers that are out there. If you'd really like, I'll look at posting some pointers to good explanations of the relational theory of data on my blog when I have time (I'm in the middle of a QA handoff right now, so I have little time for serious research). The starting points I mentioned earlier, though (Wikipedia and the c2 wiki) are really good and get you ready for understanding much of what Fabian Pascal and Chris Date say. One of these days I will buy the Third Manifesto, but right now, I have far too much to do otherwise. -austin -- Austin Ziegler * halostatue@gmail.com * http://www.halostatue.ca/ * austin@halostatue.ca * http://www.halostatue.ca/feed/ * austin@zieglers.ca