Lambda the Ultimate

Is Pascal's preference for Codd's relational model over models based on graph theory as dogmatic as it sounds?

Pretty much, yes. C.J. Date and Pascal have been singing this song for a while (the relational model is the perfect data model, why has everyone screwed it up, why does everyone neglect it, etc.)

On the other hand, they do make some interesting points about the shortcomings of XML.

Dominic: I think Pascal's style of argumentation is a model of how not to do it

Heh, when I first started reading Pascal's diatribes I had the uncomfortable feeling that I was reading my own posts. :) I really understand their frustration, but I agree that they could pursue more fruitful methods to achieve their goals.

However I generally agree with Pascal's and Date's points, inasmuch as I can understand them, being something of a database outsider.

Marc: the relational model is the perfect data model

I don't think they're saying this. They're saying that, of the known data models, it is the best because it's the most general, the best understood, the most `complete' and the simplest. See the `desirable properties of a data model' at the end of Tags Do Not a Language Make - Part 1.

(I would make a similar argument in favor of typed functional languages.)

why has everyone screwed it up, why does everyone neglect it

Yeah, there is probably too much political content in Pascal's essays. I have also developed some opinions about why static and dynamic typing are so misunderstood, and occasionally considered whether it might be best to air them (and probably sometimes let them slip), but on the whole I think I'm not qualified to psychoanalyze programmers or analyze the industry or its history.

On the other hand, they do make some interesting points about the shortcomings of XML.

Yes, particularly the bit about syntax versus semantics, which echoes my own feelings.

OTOH, as W3C standards go, XQuery is a step in the right direction in terms of implementation. What I mean is, even though I don't like the design goals of XQuery or see a need for it or most of its features, the way in which they are meeting those criteria is better than usual; for example, there is a formal semantics.

However, I'm a bit mystified about the way they associate hierarchical models with graph theory. I don't know exactly what a hierarchical database model is, but I would associate it with the theory of trees. And I imagine you can achieve the same level of expressiveness as a relational model by quotienting a hierarchical model with some equations. (Would they call that a relational model again, then?) Probably they are as ill-informed about PLT as I am about DB theory, though, so I guess this is more due to miscommunication than genuine error.

They're saying that, of the known data models, it is the best because it's the most general, the best understood, the most `complete' and the simplest.

I agree that this is what they are saying, and I would even agree that it is true for general purpose data problems, but I think that what they miss is that sometimes you don't need all that generality or completeness, and as a result there is a simpler solution for a specific problem.

To the extent that XML is touted as the cure-all for data transfer and storage problems, there criticism is on target. But I think they sometimes throw the baby out with the bath water; sometimes an annotated tree is just what you want.

However, I'm a bit mystified about the way they associate hierarchical models with graph theory. I don't know exactly what a hierarchical database model is, but I would associate it with the theory of trees.

I think this may simply be imprecision on their part. A tree can of course be construed as a directed acyclic graph, and I think this is what they mean, though of course this ignores a whole universe of interesting graphs.

XQuery is a step in the right direction in terms of implementation.

If Wadler works on something I take it seriously. ;-)
However, my impression from reading his XML related papers is that he basically feels that XML sucks, but he sees it as a challenge to provide formalisms and tools that make it suck less. ;-)

Poor even by slashdot's standards, but here it is...