I'm hoping someone can validate my understanding. From what I can tell through
performance measuring, using fn:not() does not automatically my a query
unsearchable (ie, not go against the index).
Given XML files in the DB that look like this :
<stuff>
<child>Alan</child>
</stuff>
where there will always be a child element but there may or may not be a value.
If I write an XPath expression like this:
/stuff[fn:not(child/text())]
Then according to xdmp:plan(), the XPath is fully searchable, and according to
the profiler, runs without a performance penalty because of the fn:not().
So my questions are: Are the absences of element values as fast as (or nearly
so) as existing values in terms of using the indexes in queries? In other
words, is querying for the absence of a value as fast as querying for a value?
Is there a faster way to query for an absent or empty value? I could change the
data so that there would be no "child" element if there is no value for the
element. Would that matter in terms of performance? Would it be faster to have
"<child values-exists='no'></child>" and use that attribute in a positive query
rather than just <child/> with a negative query?
>From my testing, it seems like using fn:not() in this case is just as good as
>anything else. But I suspect there's more to the story.
Thanks,
Ryan
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