BaseX-Talk August 2014

basex-talk@mailman.uni-konstanz.de

31 participants
59 discussions

locking problem
by Lizzi, Vincent 13 Aug '14

13 Aug '14

I've written a process using the Java BaseXClient to load XML documents to one database (A) and save a small amount of data about each document in a second database (B) using a parallel document path. The data in (B) includes a sha1 hash which is used to determine if the source XML document has changed or not to avoid unnecessary reloading. With database (A) the replace command is used to import documents. With database (B) a query is run to get the current sha1 hash (if any) and the db:replace() function is used to create/update a document for each document in (A). This works well for small sets of documents, often loading several documents per second. However after 1,000 - 4,000 documents it eventually crashes with this exception: [bxerr:BXDB0002] Database (B) is being updated, or update was not completed. The exception is thrown when reading the sha1 hash from (B). After this exception, it's not possible to connect to database (B) even with the BaseX GUI unless I manually delete the upd.basex file. I have to delete both databases and try again. No other processes are accessing the databases. It seems like this problem is related to the high number of reads and writes happening on (B). Has anyone encountered a similar problem or have any suggestions? Thanks, Vincent

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Best way to do dynamic XPath evaluation
by Paul Swennenhuis 10 Aug '14

10 Aug '14

Suppose I have a variable $xml containing the XML fragment <places><village>Wismar</village><city>Amsterdam</city><village>Positano village, Italy</village><city>Prague</city></places> In a static world I would list all cities with the XPath expression $xml//city . And the villages with $xml//village . OK. No issues. Runs fast. Now suppose I want the user to decide whether to list either cities or villages. There are several ways to implement this, but I'm looking for the dynamic XPath solution. Suppose the users choice ("city" or "village") resides in the string $choice Something like $xml/$choice abviously will not work. It will yield the string "village" or "city" 8 times (for all element and text nodes) xquery:eval() does not help either. xquery:eval($xml/$choice) is not valid, nor is $xml/xquery:eval($choice) or any variant of these, with or without parentheses or curly braces. One way I have found to do it is like this: xquery:eval(concat(fn:serialize($xml),$choice)) Complete query: let $xml := <places><village>Wismar</village><city>Amsterdam</city><village>Positano village, Italy</village><city>Prague</city></places> let $choice := '//village' return xquery:eval(concat(fn:serialize($xml),$choice)) But obviously, this executes very slowly because the XML has to be serialized. So is there any other way to do dynamic joining of XML fragments and XPath expressions given as string? Oh, BTW, I am NOT looking for this solution: $xml//*[local-name()=$choice] Thiis may work for this case but not for other XPath expressions.

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Re: [basex-talk] Best way to do dynamic XPath evaluation
by Dirk Kirsten 10 Aug '14

10 Aug '14

Hi Paul, it should be all there in the documentation I linked to. I really don't know more than the documentation already says :) So to quote: "Variables and context items can be declared via $bindings. The specified keys must be QNames or strings: - If a key is a QName, it will be directly adopted as variable name. - It a key is a string, it may be prefixed with a dollar sign. Namespace can be specified using the Clark Notation. - If the specified string is empty, the value will be bound to the context item." So the third bullet points applies here. Cheers, Dirk On 10/08/14 21:56, Paul Swennenhuis wrote: > Hi Dirk, > > Cool! Exactly what I was looking for, and it executes fast as well. > This is a life-saver for me. > > Could you elaborate a bit on the "Using the empty string for the binding > binds the element as context item (thus it must be a document)." remark? > I'm not sure if I follow that... > And what are the other binding options? > > Thanks a lot. > > Paul >> Hi Paul, >> >> xquery:eval() should be capable of doing what you want. Take a look at >> the first example at https://docs.basex.org/wiki/XQuery_Module >> >> Using the empty string for the binding binds the element as context item >> (thus it must be a document). So the following should work for you: >> >> xquery:eval($choice, map { '': document {$xml}}) >> >> Cheers, >> Dirk >> >> On 10/08/14 21:15, Paul Swennenhuis wrote: >>> Suppose I have a variable $xml containing the XML fragment >>> <places><village>Wismar</village><city>Amsterdam</city><village>Positano >>> village, Italy</village><city>Prague</city></places> >>> In a static world I would list all cities with the XPath expression >>> $xml//city . >>> And the villages with $xml//village . >>> >>> OK. No issues. Runs fast. >>> >>> Now suppose I want the user to decide whether to list either cities or >>> villages. >>> There are several ways to implement this, but I'm looking for the >>> dynamic XPath solution. >>> >>> Suppose the users choice ("city" or "village") resides in the string >>> $choice >>> Something like $xml/$choice abviously will not work. It will yield the >>> string "village" or "city" 8 times (for all element and text nodes) >>> xquery:eval() does not help either. xquery:eval($xml/$choice) is not >>> valid, nor is $xml/xquery:eval($choice) or any variant of these, with or >>> without parentheses or curly braces. >>> >>> One way I have found to do it is like this: >>> >>> xquery:eval(concat(fn:serialize($xml),$choice)) >>> >>> Complete query: >>> >>> let $xml := >>> <places><village>Wismar</village><city>Amsterdam</city><village>Positano >>> village, Italy</village><city>Prague</city></places> >>> >>> let $choice := '//village' >>> >>> return >>> xquery:eval(concat(fn:serialize($xml),$choice)) >>> >>> >>> But obviously, this executes very slowly because the XML has to be >>> serialized. >>> >>> So is there any other way to do dynamic joining of XML fragments and >>> XPath expressions given as string? >>> >>> Oh, BTW, I am NOT looking for this solution: >>> $xml//*[local-name()=$choice] >>> Thiis may work for this case but not for other XPath expressions. >>> >>> > -- Dirk Kirsten, BaseX GmbH, http://basex.org |-- Firmensitz: Blarerstrasse 56, 78462 Konstanz |-- Registergericht Freiburg, HRB: 708285, Geschäftsführer: | Dr. Christian Grün, Dr. Alexander Holupirek, Michael Seiferle `-- Phone: 0049 7531 28 28 676, Fax: 0049 7531 20 05 22

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fn:trace and http-server, why is it not logged?
by Marc van Grootel 10 Aug '14

10 Aug '14

Hi, I used fn:trace in code and I made sure it is not optimized away. Saw the trace msg in the gui. But when doing it via the http server only the standard request info is shown in the log 18:05:47.810 0:0:0:0:0:0:0:1:50364 admin REQUEST [GET] http://localhost:8984/ 18:05:49.234 0:0:0:0:0:0:0:1:50364 admin 200 REQUEST 1463.52 ms 18:05:49.235 0:0:0:0:0:0:0:1:50364 admin 200 0.32 ms The docs say that trace is sent to stderr, isn't that logged? Is there a way to turn the logging volume for http server logging up a notch or is there some other way to get the trace messages logged? -- --Marc

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BaseX & XQuery 3.1: Arrays
by Christian Grün 09 Aug '14

09 Aug '14

Dear all, As you may have heard, XQuery 3.1 will not only provide maps (which have been around in BaseX for quite a while now) but also arrays... And we are pleased to announce that, since today, arrays are available in BaseX! Some of the new features are documented in our Wiki: http://docs.basex.org/wiki/XQuery_3.1 http://docs.basex.org/wiki/Array_Module Please note that the XQuery 3.1 spec. is at an early stage and subject to change, but the implementation is already fully functional, and we are looking forward to receiving your first feedback. The latest 8.0 snapshot is now available at: http://files.basex.org/releases/latest/ Have fun, Christian

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unexpected behaviour xquery:update()
by Rob Stapper 09 Aug '14

09 Aug '14

Hi, See attachment: "XML update example 2.sq" What happens to the output of this program? I don't see any results in the GUI. Rob --- Dit e-mailbericht bevat geen virussen en malware omdat avast! Antivirus-bescherming actief is. http://www.avast.com

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running in eclipse
by Andy Bunce 09 Aug '14

09 Aug '14

Hi, I am having problems running the source. I have download the zip from github, and added as a java project in eclipse. When I run I get... /lang/English.lang not found. English.lang: 'srv_started_port_%' is missing English.lang: 'srv_stopped_port_%' is missing English.lang: 'srv_running' is missing What am I doing wrong? /Andy

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CSV : Content is not allowed in prolog.
by Roman Mishin 09 Aug '14

09 Aug '14

Hi, Could you, please, tell what can be wrong here. This query works: db:open("IntersectPhoneNumbers","Data/rent_flats.csv")/csv/record/UserPhone With result: <UserPhone>2218520</UserPhone> <UserPhone>2219391</UserPhone> <UserPhone>2348039</UserPhone> ... I can access the file directly from the query, without adding it into a database. This also does work, giving the same result: let $csv := file:read-text(fn:resolve-uri('Data/rent_flats.csv')) let $rent_flats := csv:parse($csv, { 'header': true(), 'separator': 'tab' }) return $rent_flats/csv/record/UserPhone But this does not work: doc("Data/rent_flats.csv")/csv/record/UserPhone Error: [FODC0002] "C:/Projects/IntersectPhoneNumbers/Data/rent_flats.csv" (Line 1): Content is not allowed in prolog. Though I can browse the file from BaseX GUI. It is in DB. Selecting nodes in Folder Pane for that file, shows the actual data in Result Pane. I can also access all records from all files in Data folder, including rent_flats.csv: /csv/record/UserPhone But I wish to refer to rent_flats.csv only. Why is this error? I am using BaseX 7.9 on Windows XP SP3. -- Roman

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map:for-each-entry missing from latest 8.0
by Marc van Grootel 08 Aug '14

08 Aug '14

Hi, I intended to use the 8.0 documented function map:for-each-entry but it doesn't exist (tried latest snapshot). So I thought I open modules.zip to look at the code. And, indeed it wasn't there. Second thing I noticed was a typo in the namespace. http://www.w3.org/2005/xpath-functsions/map this should be: http://www.w3.org/2005/xpath-functions/map Let me know if you need me to log it somewhere. --Marc

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How to update a XML-file from itself?
by Rob Stapper 08 Aug '14

08 Aug '14

Hi, Can anyone help me with this casus? I want to update XML-source: $a, by inserting the content of XML-element: $b, a sub-element of $a, into XML-element: $c, also a sub-element of $a. The relative path from $b to $c is known. See attached example: the problem is that the update works on a copy of $a and that the destination-element: $b/parent::*/default/text1, is actually an element of the original $a. How can I make it point to the corresponding element in the copy? Any suggestions? Thanx in advance, Rob Stapper --- Dit e-mailbericht bevat geen virussen en malware omdat avast! Antivirus-bescherming actief is. http://www.avast.com

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BaseX-Talk August 2014