BaseX-Talk December 2011

basex-talk@mailman.uni-konstanz.de

29 participants
46 discussions

Precompiling Queries
by Dave Glick 21 Dec '11

21 Dec '11

Hello again, I notice in the current sources for QueryProcessor.java that executing a query appears to be a three-stage process: parse, compile, and execute. Is it now possible to preparse and/or precompile a query before using it? If so, this raises a couple important questions: - Does executing the query "destroy" it (will subsequent executions return the same results)? - What can be done to the query after parsing or compiling? Can I rerun a query after changing the context? What about after adjusting the variable bindings? I notice that doing either of these in QueryProcessor does not reset the parse or compile flag... The last time I looked at this, neither of the operations above were possible making preparsing and precompiling kind of pointless for embedded use. If this works now, it's very exciting and could save a lot of cycles in cases where a complex query needs to be repeatedly executed against different contexts or with different variables. Thanks, Dave

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Possible Optimization Bug (Or Maybe Document Insertion Bug)
by Dave Glick 20 Dec '11

20 Dec '11

Hello, I seem to have stumbled on a bug (or at least I think I have). Do the following: - Create a simple database with a single document - Insert a text node before the start of the document root ("insert node "test" before /root") - Attempt to optimize the database You will get a NullPointerException at org.basex.index.Names.index(Names.java:84). It appears as though the index is attempting to set statistics information for key id 0 (because the parent is a document), but the stats[] array only gets initialized with objects from index 1 and up. The other possibility is that text nodes should not be allowed before or after the document root element. I'm a little hazy on what the standards say in this regard. My understanding is that the document node can have prolog content before the root and other content after. I've also seen many documents which parse correctly that have text content before the opening tag (though again, this may not be strictly standard-compliant behavior). If this is the case, then the bug is probably that the insertion update operation is allowed to succeed. Dave

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Re: [basex-talk] Possible Optimization Bug (Or Maybe Document Insertion Bug)
by Dave Glick 20 Dec '11

20 Dec '11

Christian, Try the following: "create db db <a/>;xquery insert node "text" before /a;optimize" This gives me the error reported below. I ran it from the GUI, though I'm guessing that shouldn't make a difference. It appears as though the difference is in the insertion of text content (as opposed to node content). Though I now see three possible problems (or not) based on your example and its success: - A NullPointerException during optimize after inserting text content before the root element of a document. - The ability to insert text content before the root element of a document (should this be allowed?) - The ability to insert a second node before the root element of a document (should this be allowed?) Dave -----Original Message----- From: Christian Grün [mailto:christian.gruen@gmail.com] Sent: Tuesday, December 20, 2011 4:34 PM To: Dave Glick Cc: BaseX Subject: Re: [basex-talk] Possible Optimization Bug (Or Maybe Document Insertion Bug) Dave, thanks for the valuable observation and the hints what could be the reason. I didn't manage to reproduce the problem, though. This is what I tried: basex -c "create db db <a/>;xquery insert node <b/> before /a;optimize" Do you have a little example that leads to the discussed problem? Next, I'll also be glad to look at one of the documents with text before the root node that is erroneously accepted by our parser. Thanks! Christian ___________________________ On Tue, Dec 20, 2011 at 6:32 PM, Dave Glick <dglick(a)dracorp.com> wrote: > Hello, > > I seem to have stumbled on a bug (or at least I think I have). Do the following: > > - Create a simple database with a single document > - Insert a text node before the start of the document root ("insert > node "test" before /root") > - Attempt to optimize the database > > You will get a NullPointerException at org.basex.index.Names.index(Names.java:84). It appears as though the index is attempting to set statistics information for key id 0 (because the parent is a document), but the stats[] array only gets initialized with objects from index 1 and up. > > The other possibility is that text nodes should not be allowed before or after the document root element. I'm a little hazy on what the standards say in this regard. My understanding is that the document node can have prolog content before the root and other content after. I've also seen many documents which parse correctly that have text content before the opening tag (though again, this may not be strictly standard-compliant behavior). If this is the case, then the bug is probably that the insertion update operation is allowed to succeed. > > Dave > > > _______________________________________________ > BaseX-Talk mailing list > BaseX-Talk(a)mailman.uni-konstanz.de > https://mailman.uni-konstanz.de/mailman/listinfo/basex-talk

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database corruption after update query
by Adrian Hossu 20 Dec '11

20 Dec '11

Hello all, first the info: basex 7.0.2 debian 64bit jre 1.6.0_30-b12 We are experiencing some strange behaviour with basex - certain update queries are causing our database to become corrupted, and we need to drop the database and re-import in order to be able to continue. Here is an example of such a query: replace node collection("ft")/user/user[@id='2']/logsheets/logsheet[@date='2011-12-20']/exercise[2] with <exercise/> The query executes successfully, however, executing db:list('ft') after this call gives us only garbled text. The basexgui shows the results of this as: >_'蘼 &#x16 ..................etc.... Perhaps it's the query, or our original data which we are starting with? Any help would be greatly appreciated. best regards, Adrian

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Approaches to Implement OpenID/OAuth 2.0 with BaseX
by Eric Murphy 20 Dec '11

20 Dec '11

I am looking at what may be involved to implement OAuth 2.0 for BaseX. I guess the purpose of this would be to verify credentials against a BaseX whitelist that can only be modified by a system administrator. The authentication would be required for REST access to BaseX. Has anyone already given this some thought? Thanks, Eric

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Namespace Bug!
by Truong An Nguyen 20 Dec '11

20 Dec '11

Hello, When I tried to execute the query in the file query.xq on the XML file DiagCom.otx, BaseX generated the false namespace for the following element <action>: <action xmlns="http://iso.org/OTX/StandardInterface/Event" name="GetComChannel0" id="id_f87ea71dd006450c9aa5085c9648d8e9"> (xmlns shouldn't be generated here) Could you please quickly fix this error for me? Many thanks. Cheers, An

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streaming the output to another file in BaseX database
by Huy Vu 19 Dec '11

19 Dec '11

Hello, I am writing my code in Java and the result after querying xml files in my BaseX database is very large, about 500MB. Thus, I would like to stream the output to another xml file in the BaseX database. Could you tell me how to do this? Many thanks, Huy Vu -- Huy Vu Oxford University, United Kingdom http://www.cs.ox.ac.uk/people/huy.vu/

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Using the BaseX REST interface from JavaScript
by Michael Piotrowski 19 Dec '11

19 Dec '11

Hi, I'm new at this, so please excuse if I missed something obvious... BaseX implements a REST interface via basexhttp and JavaScript frameworks like Ext JS allow you to use a REST interface for accessing data. So I thought it may be possible to create a Web interface to a corpus stored in BaseX that enables users to search the corpus and update the annotations *without* writing server-side code. The first obstacle I encountered is that under the same-orgin policy browsers consider localhost and localhost:8984 two separate domains and inhibit XmlHttpRequests calls, and basexhttp seems not to support cross-origin resource sharing (see <http://enable-cors.org/>). Using BaseX as a data store for an Ext JS component without having to write server-side code seems very attractive. However, I'm now wondering whether this approach makes sense at all. Has anybody tried to do something like this? Thanks in advance! Best regards -- Dr.-Ing. Michael Piotrowski, M.A. <mxp(a)cl.uzh.ch> Institute of Computational Linguistics, University of Zurich Phone +41 44 63-54313 | OpenPGP public key ID 0x1614A044 * OUT NOW: Systems and Frameworks for Computational Morphology * <http://www.springeronline.com/978-3-642-23137-7>

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Approaches for XML merging and conflict resolution
by Eric Murphy 18 Dec '11

18 Dec '11

All, I am looking at using BaseX for a prototype that requires synchronization of XML data. In other words, XML documents may need to be merged and there might be conflicts. This seems like a complex issue and I wonder if anyone has conquered this before. The only thing that I can think of to do is to version nodes which may have conflicts. For example: <person> <name> <first version="2">Erik</first>  <last version="1">Murphy</last> </name> </person> If I do a merge and the <first> version is >= last known version (1) + 1 ( which is 2 or greater), then I would know there is a conflict. A possible solution is there could be a deferment of conflict resolution, and data could be inserted like this: <person> <name> <first version="3">Eric</first>  <first version="2">Erik</first> <last version="1">Murphy</last> </name> </person> The application would be responsible for resolving the conflict when the nodes are read at a later time. Like I said, this all seems very complicated, so maybe there is an elegant solution which I have not thought of. Thank you, Eric Murphy

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BaseX Meetup, XML Prague
by Christian Grün 18 Dec '11

18 Dec '11

Dear all, we’re glad to announce the first BaseX Meetup aligned with the XML Prague Conference. The meetup will take place if we know that there will be enough participants on site, so.. you are invited to join in as soon as possible! http://lanyrd.com/2012/basexprague Note that your registration is non-binding, and free if you will participate at the main conference as well ...which is cheap, a really great opportunity which you shouldn't miss anyway! Find some more information on XML Prague on this page: http://www.xmlprague.cz Looking forward to meeting you live, Christian ___________________________ BaseX Team Christian Grün Uni KN, Box 188 D-78457 Konstanz http://www.basex.org

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BaseX-Talk December 2011