BaseX-Talk

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5241 discussions

A couple of technical issues
by Mark Boon 03 Dec '10

03 Dec '10

I ran into a few separate issues. Since they concentrate on the same piece of code, I address them simultaneously. In my program I have the following method: private void processEventTriggers() { try { ByteArrayOutputStream stream = new ByteArrayOutputStream(); String inQuery = "collection()/event/@in/string()"; XQuery inputQuery = new XQuery(inQuery); inputQuery.execute(_context,stream); String input = stream.toString(); String processQuery = "collection()/trigger_set/trigger[@name='"+_currentTrigger+"']/matches"; System.out.println("Process Event: "+processQuery); QueryProcessor processor = new QueryProcessor(processQuery, _context); Iter iterator = processor.iter(); Item item; while ((item=iterator.next())!=null) { BXNode node = (BXNode)item.toJava(); String pattern = node.getAttributes().getNamedItem("pattern").getNodeValue(); // Pattern regexp = Pattern.compile(pattern, Pattern.CASE_INSENSITIVE); // Matcher regexpMatcher = regexp.matcher(input); // System.out.print("'"+input+"' matches '"+pattern+"'"); // if (regexpMatcher.matches()) // System.out.println(" = true"); // else // System.out.println(" = false"); String matchQueryString = "matches('"+input+"','"+pattern+"','i')"; System.out.print("Match Query: "+matchQueryString); XQuery matchQuery = new XQuery(matchQueryString); stream.reset(); matchQuery.execute(_context,stream); if (stream.toString().equals("true")) { System.out.println(" = true"); if (executeCommands(node)) break; } else System.out.println(" = false"); } } catch (BaseXException exception) { exception.printStackTrace(); } catch (QueryException exception) { exception.printStackTrace(); } } What this does is it queries the database for an input item and then matches this input to a set of 'matches' nodes. When a node matches it starts executing a series of commands, which are mostly XQuery commands themselves. The first issue I have is that it seemed a bit inefficient to use an XQuery to match a regular expression. The section commented out matches the same regular expression. Unfortunately, I bumped into a few cases where the Java implementation mistakenly returns 'false' whereas the BaseX implementation returns 'true'. I can't complain really about BaseX here. Actually, kudos for providing a proper implementation, because I had assumed it would simply delegate this functionality to the Java regexp API. But I was a bit surprised to find that the Java regular expressions implementation seems to be broken. My question now is, can I call the BaseX 'matches()' function directly? Because I think that would be much more efficient. A more serious issue I have is that the XQueries that are executed in the 'executeCommand()' call occasionally insert and delete nodes into collection()/memory sub-elements. And it also can recursively call processEventTriggers() again. Most of the time this works fine, but occasionally I get the following error: Exception in thread "main" java.lang.RuntimeException: Possible bug? Feedback is welcome: basex-talk(a)mailman.uni-konstanz.de BaseX 6.3.2: Data Access out of bounds [pre:403, indexSize:4, access:4 > 3] at org.basex.util.Util.notexpected(Util.java:46) at org.basex.io.TableDiskAccess.cursor(TableDiskAccess.java:323) at org.basex.io.TableDiskAccess.read1(TableDiskAccess.java:92) at org.basex.data.Data.kind(Data.java:324) at org.basex.query.item.DBNode$4.next(DBNode.java:272) at org.basex.query.path.IterStep$1.next(IterStep.java:45) at org.basex.query.iter.NodeIter.next(NodeIter.java:1) at org.basex.query.path.IterPath$1.next(IterPath.java:66) at org.basex.query.path.IterPath$1.next(IterPath.java:1) at BotCommandProcessor.processEventTriggers(BotCommandProcessor.java:285) at BotCommandProcessor.processEvent(BotCommandProcessor.java:262) at BotCommandProcessor.executeCommands(BotCommandProcessor.java:364) at BotCommandProcessor.processEventTriggers(BotCommandProcessor.java:305) at BotCommandProcessor.processEvent(BotCommandProcessor.java:262) at BotCommandProcessor.main(BotCommandProcessor.java:442) Now I'm not entirely sure, but I suspect that the iterator is affected either by the insert/delete operations or by the nesting of the iterator process. Or a combination of the two. I could somehow understand this if the queries that are being executed would affect the set of triggers it's looping over, but that is not the case. I did find an ugly way around this problem but I'm afraid it could get me into trouble later. So any feed-back about what might be the best way to fix this would be appreciated. Mark Boon

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Introducing PAD Submit Worker
by ShareSoftware24 01 Dec '10

01 Dec '10

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Inserting nodes into xquery result sets
by Charles F. Munat 01 Dec '10

01 Dec '10

I have a database like this: <data> <templates> <template> <id>123</id> <content> <html> <head><title>My Template</title></head> <body><text/></body> </html> </content> </template> </templates> <pages> <page> <id>456</id> <content> <p>This is some text.</p> </content> </page> </pages> </data> I want to write an XQuery that results in this: <html> <head><title>My Template</title></head> <body><p>This is some text.</p></body> </html> So <text/> is replaced by <p>This is some text.</p> Here is the start of an XQuery select: for $x in /data/templates/template[id='123']/content/* for $y in /data/pages/page[id='456']/content/* return $x That gets me the template. How do I insert $y in place of $x/body/text ? I've searched all over with no luck. I can do this in the business logic, but so much better to do it in the query. Also, I'd like to be able to do this recursively. Is that possible? Do I have to write my own function for this? Thanks much for any help! Chas.

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Surprising function behavior
by Mark Boon 30 Nov '10

30 Nov '10

I bumped into some surprising function behavior. I have the following query: declare namespace math = "java:java.lang.Math"; declare function local:choose-phrase ( $phrase as xs:string ) as xs:string { let $prefix := local:choose( ("Absolutely, ", "It's likely that ", "The odds are good that ", "There's a fairly good chance that ", "There's a light chance that ", "It's uncertain that ", "Chances are not good that ", "It's doubtful that ", "It's unlikely that ", "There's no way that ") ) return fn:concat($prefix,$phrase) }; declare function local:choose ( $arg as xs:string* ) as xs:string { let $count := fn:count($arg) let $random := math:floor(math:random() * $count) + 1 return $arg[xs:integer($random)] }; local:choose( ( "Phrase 1", "Phrase 2" ) ) When I execute this (say in the GUI tool) it's supposed print either "Phrase 1" or "Phrase 2". Instead it prints a random choice from the function 'choose-phrase' as if it was called with an empty string as argument, which is very strange. When I remove the 'choose-phrase' function altogether, the query behaves correctly. If I then paste the 'choose-phrase' after the 'choose' function, it also behaves correctly. But declaring 'choose-phrase' before 'choose' gives me an unexpected result. The only thing I can think of is that 'choose-phrase' calls 'choose' which is declared later. I don't know if that's actually allowed. But even so, it should give an error instead of seemingly doing something random.

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Re: [basex-talk] User-defined functions
by Christian Grün 23 Nov '10

23 Nov '10

Hi Mark, (I'm passing this on to the mailing list..) > At the moment my function block is not very long. But I expect this is > likely to change, as I'm using XQuery as a sort of programming > language where 'users' can add functions. Moreover, there will be > cases where they'll be executing thousands of queries and the total > execution time should ideally take no more than a second or two in the > most extreme circumstance. > > At this time I don't experience any performance problems, BaseX is > very snappy. But I'm still in the experimentation phase and I'd like > to avoid spending a lot of time building a framework that later may > turn out to be unworkably slow. Regarding the complexity and size of function blocks, our users haven't reported any bottlenecks yet. Instead, bad performance is mainly due to XQuery expressions that are difficult, or impossible, to optimize. But, no doubt, it might make sense to precompile complex XQuery code that takes hundreds of KB, or even MB. Right now, precompilation of XQuery code isn't supported in BaseX > Another thing I ran into is that updating doesn't seem to be allowed > within functions. So I'm now looking into using XSLT to solve these > issues for me. On the one hand by prefixing the query with the > function declarations that are actually used in the query, and through > templates that would substitute updating function-calls by the > function-body. I'm also new to XSLT so I'm not sure if that will work, > but it seems worth giving it a try. Updating is no problem in XQuery functions: you'll have to add the "updating" specified to a function declaration: declare updating function ... { ... }; A general restriction of XQuery is that an expression cannot both update and output items. As an example, the following query is invalid: delete //node, 1 to 10 Instead, you can perform local updates by applying the transform expression: copy $a := ...nodes to be modified... modify ...update on $a... return ...e.g., $a... > P.S. extracting the xsl-stylesheet from the file-header from an XML > file and then applying it to itself is a bit ugly, does anyone know if > there is a (JAXP) way to get an XML file with its stylesheet already > applied automagically? Maybe this won't be necessary anymore.. Hope this helps, Christian

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basex 6.3.2 and .NET
by Maximilian Gärber 23 Nov '10

23 Nov '10

Hi all, I did some testing with IKVM and basex-6.3.2.jar and it turns out to be as simple as calling ikvmc on the .jar file to get a working basex-6.3.2.dll for .NET I adapted the DB example from http://www.inf.uni-konstanz.de/dbis/basex/code/DatabaseExample an it run without problems. Now I am curious what others have experienced using basex on .NET. And of course: what are chances that this could be supported in the future (like Saxon.net, for example) Best Regards, Maximilian

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User-defined functions
by Mark Boon 22 Nov '10

22 Nov '10

I'm fairly new to XQuery and only started to use it and BaseX last week. So far I've been very impressed with the capabilities of both. I have one question about user-defined functions. From what I can tell so far that I learned about XQuery, user-defined functions are only accessible when they are declared in the prolog of the query. In itself I suppose there's a certain logic to that. My project is most likely very atypical from your average XQuery usage, but it would be much more convenient, and probably also much more efficient if I could somehow (optionally) declare user-defined functions and reuse them for several queries in a row. I don't think importing a module would be a solution because a) that would be even more inefficient and b) I don't think it wouldn't work with dynamically created functions. (I'm executing queries that contain queries that get executed...) So I was wondering if there's a way to accomplish this. And even if this is currently not possible, would it be complicated for an accomplished Java developer to add as a custom extension? Any tips or ideas will be greatly appreciated. Mark

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Test doesn't succeed for Rev. 2715 / 2718
by Thomas 22 Nov '10

22 Nov '10

Hi, I just checked out Rev. 2718. During build, I get the following error: Running org.basex.test.server.ServerCmdTest BaseX 6.3.3 [Server] Server was started. Tests run: 34, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 2.541 sec <<< FAILURE! Server was stopped. When I uncomment the following lines in CmdTest (that have been changed in 2715), the test succeeds. l 350 ok(new Open(NAME)); l 351 no(new Restore(NAME)); l 352 ok(new XQuery(".")); The message says: java.lang.AssertionError: Database 'input' was not found. at org.junit.Assert.fail(Assert.java:91) at org.basex.test.server.CmdTest.ok(CmdTest.java:428) at org.basex.test.server.CmdTest.restore(CmdTest.java:350) The other tests succeed. Any ideas? Greetings, -- Thomas

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Specify a custom document name containing spaces
by Daniël Knippers 18 Nov '10

18 Nov '10

Hi everyone, I have a question regarding the add command -- ADD (AS [name]) (TO [target]) [input]. It seems it is not possible to add a document to the database which you want to give a custom name (for whatever reason) that contains a space like so: add as "test x.xml" "/path/to/test 1.xml" Doing this will result in an error implying I do not use the right syntax. Apparently it is not allowed to use quotes (neither " nor ') around the name you want to give the document. I wonder why this is. Especially because BaseX will actually name the document 'test 1.xml' when the 'as [name]' is omitted; like so: add "/path/to/test 1.xml" I wonder if this is a minor bug in the syntax checking of this command, or that this is intended behavior. In case of the latter, I wonder if there is another way to specify names which contain spaces. While we are at it (the add command): I was expecting the TO [target] part to refer to a database. For example, if I have two databases 'misc' and 'col', I would expect a command such as: add to misc "/path/to/test.xml" to add the document test.xml to the database misc. Instead, I first have to open the database misc, then add the document (without the 'to misc'-part), then close it again. Is this also intended? If so, please enlighten me as to what target exactly refers to (apparently no database/collection). Thanks in advance for any responses. -- Daniël ps. I am on version 6.3.1

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Util.applicationPath based on ProtectionDomain returns unintended context-/app-location
by Thomas 18 Nov '10

18 Nov '10

Hello everyone, I'm new to BaseX. Just evaluating if it fits in my current project. Looks great. My project uses maven, BaseX 6.3.2 is added as a dependency according to your documentation. Here comes the problem: The resolution of the Prop.HOME-Directory (thus the location of the props-file ".basex") doesn't fit the intended behavior (as far as I got the intention), when using (Netbeans and) maven for build and run. And it should not work as intended when placing the basex-jars in a lib-directory as well. AFAIK, it's supposed to be a directory relative to the path in which the application got executed (if props ".basex" are found there, otherwise the users home directory). (If however the current path should be the intended one, then I'd say it's not very intuitive or practical) Using (Netbeans and) maven for build and run, causes the relative path to result in the maven-repository-location of the xbase-jar. (e.g. "{repository-root}/.m2/...") That's definitely no place for a props-file, so it will always result in the user-home-directory. I don't want to pollute the users home directory however (besides we plan to make the app portable), that's why I was wondering if you could detect the relative path in another way. Here's the details of what's currently happening: The creation of the Database: Class<?> c = Class.forName(DRIVER); Database db = (Database) c.newInstance(); causes several initializations to happen. Among others, there's the static initializer of Prop (line 38), which calls Util.applicationPath() to calculate the HOME directory. The method body of applicationPath starts with final String path = Util.class.getProtectionDomain(). getCodeSource().getLocation().getPath(); which returns the location of the jar in the maven repository, which is not the application path (and could result in a completely unintended path when using custom-classloaders). Suggestion: Could you just calculate the working directory like this: final String path = new File(".").getPath(); or final String path = new File(".").getAbsolutePath(); This would IMHO result in a more intuitive location for the working- (or config-)directory. I'd suggest to put that into a new method, say Util.workingPath() (or Util.configPath()), to prevent trouble with code, that actually needs to receive the jar-file-location (if such code exists at all). To stay compatible with the old resolution strategy, you could just add this line of code on top of the old resolution, thus provide a third location for props. I'd contribute this patch by myself, if you'd agree. Future needs for my application are dynamic configuration of port-ranges and stuff, that's why I'd also love to have the opportunity to configure BaseX completely by the use of the API, without having to deal with config-files for "third-party-libs". BaseX looks great and I'd love to use it for my project if it proves to be adequate. Great work! Greetings, -- Thomas

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