Hi Giuseppe,

Your summary is 100% correct, and surely helpful to other users.

An even better option than using data() is the ENFORCEINDEX option, which was added with BaseX 9. It allows you to enforce index rewritings for the whole query, or for specific comparisons or predicates.

I noticed it was restricted to comparisons with static values, which is something I have just changed. The following query should be faster than the original version:

for $s in db:open("ru_syntagrus-ud-dev")//s//t for $d in db:open("UD_Russian-SynTagRus")//case where (# db:enforceindex #) { $d/verb_lemma = $s/@l } and $d//verb_form/@value = $s/@f and $d/aspect-values/@sign = "yes" return $s

I have added some words on this enhancement in the documentation [1]. Feel free to check out the new snapshot [2], Christian

[1] http://docs.basex.org/wiki/Indexes#Enforce_Rewritings [2] http://files.basex.org/releases/latest/

On Thu, May 24, 2018 at 11:18 AM, Giuseppe Celano celano@informatik.uni-leipzig.de wrote:

Hi Christian,

Thank you for your help! To summarize (also for the benefit of other users), while it is true that in XQuery data($d/aspect-values/@sign) = "yes" and $d/aspect-values/@sign = "yes" are equivalent (because of atomization), the use of data() enables the user to prevent the use of a certain index in BaseX (so this is a BaseX-specific feature). Paying attention to how BaseX uses indexes (which can be seen in the GUI Info panel) seems to be particularly important when join operations between documents are done: as far as I understand, which index and how these indexes are used automatically by BaseX cannot be predicted in advance, so what one can do is to actually try to use the data() function in order to test which index use turns out to be the best (especially when the query evaluates slowly).

Is this correct?

Thank you again! Giuseppe

Universität Leipzig Institute of Computer Science, NLP Augustusplatz 10 04109 Leipzig Deutschland E-mail: celano@informatik.uni-leipzig.de E-mail: giuseppegacelano@gmail.com Web site 1: http://www.dh.uni-leipzig.de/wo/team/ Web site 2: https://sites.google.com/site/giuseppegacelano/

On May 23, 2018, at 2:44 PM, Christian Grün christian.gruen@gmail.com wrote:

Hi Giuseppe,

I think your observation was related to another issue that has already been fixed recently. Did you try the latest snapshot [1]?

Btw, in your specific query I noticed that the data() may indeed be helpful to suppress the index rewriting for the last condition. As it’s the only one that has a static comparison string, it will be the one that will be chosen for index access, but for your data, it will actually be better if one of the other two conditions will be evaluated by the index.

Thanks for the sample documents, Christian

PS: 9.0.2 will be available until end of May.

[1] http://files.basex.org/releases/latest/

On Tue, May 22, 2018 at 5:22 PM, Giuseppe Celano celano@informatik.uni-leipzig.de wrote:

I think I have identified a problem with atomization of attribute content (no database involved). I have a simple query:

for $s in doc("doc1")//s//t for $d in doc("doc2")//case where $d/verb_lemma = $s/@l and $d//verb_form/@value = $s/@f and $d/aspect-values/@sign = "yes" return $s

In order to get a result, I (necessarily) need to use the data() function in data($d/aspect-values/@sign) = "yes", otherwise the query never returns a result. Is this a bug? I would expect that the value of @sign is automatically atomized and compared to "yes", but this does not seem the case. Thanks.

Ciao, Giuseppe

Universität Leipzig Institute of Computer Science, NLP Augustusplatz 10 04109 Leipzig Deutschland E-mail: celano@informatik.uni-leipzig.de E-mail: giuseppegacelano@gmail.com Web site 1: http://www.dh.uni-leipzig.de/wo/team/ Web site 2: https://sites.google.com/site/giuseppegacelano/