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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Modern talking
 Recently, drowsing in a park, I became an involuntary witness of the following conversation. Kolodopolus: Do you know what XQuery is? Gaius: Sure, kind of SQL for XML, right? K: I do not think that you understood well. G: (raises eyebrows) K: XQuery is a unified view of information. G: Pardon? K: A view answering two questions: What is information? What is an operation applied to information? G: So, what is information? K: A value. G: What's a value? K: A sequence of items. G: What's an item? K: Either a node, or an atom, or a map, or an array, or a function. G: A function is ... K: ... a mapping of values to a value. G: And what is an "operation applied to information"?K: It is an expression - a mapping of values (operands) to a value (the expession value). G: Is XQuery mathematics, or philosophy? K: Neither, or perhaps the translation of both into technological reality. G: You don't expect me to understand what you mean? K: It defines the syntax and semantics of a few dozens of expressions. At the heart of it all is the so-called path expression, which is about addressing tree-structured information. XQuery expressions are fully composable building blocks from which to construct processings of arbitrary complexity. G: A mental world of expressions, with values flowing in and values flowing out! K: Yes, sir. G: I'm not blind to the intellectual beauty of such a closed system. But is it useful? Especially as the popularity of XML is declining?K: XQuery has nothing to do with XML. G: (laughts) K: It's about information. G: So in which context might XQuery be useful, and how? K: A key field is DATA INTEGRATION. G: Perhaps you give me an example? K: Sure. Imagine you have a directory tree containing many .csv files. All of these should be constrained to contain in their third column only values found in a term list provided by yet another file, which is a JSON file. How would you check? G: No problem, half a page of Python, I suppose ... K: With XQuery it is a single expression, a single line spread over three for the sake of readibility. G: Show me! K: (picks up a stick and draws into the dust:) let $dir := "/path/to/my/dir" return empty( file:list($dir, true(), "*.csv") ! concat($dir, '/', .) ! unparsed-text(.) ! csv:parse(.)/*/*/*[3] [not(. = unparsed-text($dir || '/foos.json') ! json:parse(.)//foo/_)]) G: Not bad. I notice you use extension functions defined by BaseX, not part of the official standard. K: That's right. G: So when will the next version of the standard be out, to make such things possible in a purely standards-based way? K: There won't be a next version of the standard. G: Wait a minute - if XQuery gives us a radically new way of thinking information in a unified way - is this not like a road on which we have hardly begun to walk? K: (Gets up.) This you should ask the W3C. 
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