RE: Against the Grain: Pascal commentary about XML and databases
>I keep hoping that there is some middle ground where the rigorous mathematics of the >relational model and the pragmatic usability of XML can meet and inform one another. In >private correspondence, Mr. Pascal assured me that a truly mathematical model of XML is >impossible, but I'm keeping an open mind. Hehe, this is pretty good reading. The only reason that RDBMS software dominates the market right now is because we are good at solving these problems, and RDBMS design has evolved to disallow users from asking questions that the database isn't good at answering. The fact that we ship databases that only permit things that we know how to answer efficiently does NOT imply that we will never be able to answer other questions more efficiently (in fact, RDBMS systems have evolved and gobbled up much of the research on data warehousing to include those techniques into the engines -- witness materialized views and bitmapped indexes). It is quite easy to see a trend in the industry that shows consistent continual progress at solving hard query problems. Of course some problems will always be hard (distributed cost-based query optimization is one), but I would point out that research on RDBMS optimizations has tapered off quite a bit and we have seen major increases in research geared towards semi-structured data in the past decade. So we are simply easing off on some of the traditional RDBMS constraints and beginning to allow things like recursive self-joins, ragged hierarchies, etc. and we are optimizing these things. I mean, we already solved the RDBMs optimization challenge (and remember that there were people predicting that SQL would never fly back in 1980) and now it is time to move to the next thing. XML seems like a very appropriate evolutionary step. As for saying that a truly mathematical model of XML is impossible; XML is simply a node-labeled graph. This is about as pure a discrete mathematics concept as you can get. It is easy to find graph traversal challenges that are NP-hard or need O(n^2) or worse. So? I think that areas of discrete mathematics that deal with graphs are currently the most vibrant area of research in the industry. The web itself is one huge graph structure, and research on ways to index the web, optimize routing, etc. all feed directly into techniques for optimizing XML processing. And it seems that TSPs and NP-Optimizations are all the rage these days. XML *is* math, and it's the *cool* math these days. Data processing married with XML is about as real as it gets. But I know this is all twice-told tale for you Mike. Regards, Joshua
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