In pure generic XQuery there is one output;
So if you want 7 outputs you need to either produce a "sequence" of 7 items or
a single document encapsulating them.
To produce a sequence you don't actually need to collect the values just let
them evaluate
let $doc = doc("huge.xml")
return ( filter1($doc) , filter2($doc) .... )
TO produce a wrapped element is similar
let $doc = doc("huge.xml")
return <allofthem><filter1>{ filter1($doc) }</fillter1><filter2>{
filter2($doc) } </filter2> ..... </allofthem>
----------------------------------------
David A. Lee
[email protected]
http://www.xmlsh.org
-----Original Message-----
From: Ihe Onwuka [mailto:[email protected]]
Sent: Monday, January 13, 2014 7:52 PM
To: David Lee
Cc: [email protected]
Subject: Re: [xquery-talk] Multiple output via a stream of filters
I only read the ginormous XML once... I apply the 7 filters to each node read
and it gets allocated to one of the 7 output buckets (hows that for a
semantically neutral term).
On Tue, Jan 14, 2014 at 3:50 AM, Ihe Onwuka <[email protected]> wrote:
> Input .... ginormous xml document containing data relating to a credit
> card application that I only want to read once.
>
> Filters. - under 25's, college educated, single mother, bankrupts, 6
> figure income, repeat applicants, self-employed.
>
> 1 input - 7 outputs
>
> All applicants that meet the criteria of a given filter are copied to
> the output corresponding to that filter.
>
> We could camouflage the 7 outputs into one by wrapping an element
> around the whole 7.
>
> On Tue, Jan 14, 2014 at 3:42 AM, David Lee <[email protected]> wrote:
>> A Single XQuery invocation has only one "output stream" ... but when your
>> working in a database often you don't need any, you want to put the data
>> back into the database.
>> Functions don't have "streams" really either although the word is overloaded.
>> One way it to produce a "sequence" of results which you then do something
>> with, either output in the main output or store into the database (as
>> separate documents).
>>
>> Also I believe eXist has functions for writing to files so your question my
>> have more relevance on the exists mailing list.
>>
>> But if what I think you mean by "stream" is a long result ... and
>> your dealing with GB+ data you need to be very careful, True "streaming" is
>> very hard to achieve in XQuery. Functions don't "stream" they return values.
>> XPath doesn't "stream" ... there is no real "streams" in XQuery ... so if
>> your not careful you end up with having to hold the entire result set in
>> memory.
>> But if your output is to the 'main' output (is this an HTTP call ?) you
>> might be able to stream to it .. all depends on the vendor implementation.
>>
>> I suspect what your really after is to write multiple results to either
>> documents or files.
>> XQuery doesn't support this generically but XML Databases like eXist do so
>> you might want to ask there.
>>
>> Or I may have completely misunderstood your question.
>>
>>
>>
>> ----------------------------------------
>> David A. Lee
>> [email protected]
>> http://www.xmlsh.org
>>
>> -----Original Message-----
>> From: Ihe Onwuka [mailto:[email protected]]
>> Sent: Monday, January 13, 2014 4:56 PM
>> To: David Lee
>> Cc: [email protected]
>> Subject: Re: [xquery-talk] Multiple output via a stream of filters
>>
>> If it helps think of an entity that entails a bazillion fields like a credit
>> card application and you have multiple ways you wish to classify it. So you
>> have a filter for each classification scheme and the application "filters"
>> through to the output stream of whichever predicates return true.
>>
>>
>>
>> On Tue, Jan 14, 2014 at 12:38 AM, David Lee <[email protected]> wrote:
>>> Could you define what you mean by "output" ?
>>>
>>> ----------------------------------------
>>> David A. Lee
>>> [email protected]
>>> http://www.xmlsh.org
>>>
>>>
>>> -----Original Message-----
>>> From: Ihe Onwuka [mailto:[email protected]]
>>> Sent: Monday, January 13, 2014 4:19 PM
>>> To: David Lee
>>> Cc: [email protected]
>>> Subject: Re: [xquery-talk] Multiple output via a stream of filters
>>>
>>> On Mon, Jan 13, 2014 at 11:54 PM, David Lee <[email protected]> wrote:
>>>> If your running in exist then pure XQuery is probably as good or better
>>>> then anything else.
>>>> Could you expand on your problem ?
>>>>
>>>
>>> I have a collection. Suppose I have 10 different outputs I want and the
>>> decision as to which output a node is routed to (not necessarily mutual
>>> exclusive though) can be encapsulated in a predicate (hence amenable to a
>>> filter HOF).
>>>
>>> I only want to iterate over the collection once but I wish to apply the 10
>>> predicates to each node in the sequence so as to determine which of the 10
>>> outputs (again not necessarily mutually exclusive) the node will feature in.
>>>
>>> The algorithm is straightforward using structural recursion (or tail
>>> recursion if tail call elimination is an issue). Asking whether there is an
>>> idiomatic XQuery solution that is different from this.
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