Re: [xsl] How to express this in XPath: "when condition do action" where condition cannot be evaluated until data arrives later

["BR Chrisman brchrisman@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

if these are a static set of files in a directory, then what you are doing
is joining the cars-observed database/table with the stolen-cars
database/table.
I would make a single file out of the cars-observed files like in bash:
( echo "<Observed>"; trap 'echo "</Observed>"' EXIT; cat
/path/to/files/wildcard*.xml ) | xslt style-sheet.xsl -

then in style-sheet.xsl lookup/reference the cars in the stolen-db with
document('/path/to/stole/cars/list')//Car[LicensePlate...


If you're instead trying to take a sequence of xml files and run an xpath
expression *only* on them 'as they come in', I'd join each observed xml
file with the stolen db.

while read observedFileName; do
    ( echo "<Cars>"; trap 'echo "</Cars>" EXIT; cat $observedFileName
stolen-cars.xml; ) | xmllint --xpath
'count(/Cars/Car[LicensePlate=/Cars/PoliceReports//LicensePlate]) > 0' - |
grep -qsx true && echo "$observedFileName has a stolen car in it!"
done
(would actually output xml from there, but it's probably better to invoke
xslt at that point..)

if it needs to be mechanized in some old-school batch processing type
system, I'd use 'inotifywait' to trigger on non-empty directory..

(I think there are probably 1.5 people in the world who use xmllint
(libxml2) on the linux/bash cmdline a lot...)

On Mon, Dec 19, 2022 at 10:45 AM Roger L Costello costello@xxxxxxxxx <
xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:

> Hi Folks,
>
> I have an XSLT program that processes XML files in a folder. Some of the
> XML documents contain data about a car, like this:
>
> <Car>
>     <Make>Toyota</Make>
>     <Model>Avalon</Model>
>     <LicensePlate>12345</LicensePlate>
> </Car>
>
> At some point the XSLT program reads in that XML document and begins
> processing it. The objective of processing is to output the license plate
> number if the car is stolen and "" (not stolen) otherwise. However, the
> document does not contain the necessary information to make that decision.
> The information to make the decision arrives some time later, in another
> document:
>
> <PoliceReport>
>     <Car>
>         <LicensePlate>12345</LicensePlate>
>         <Status>Stolen<Status>
>     </Car>
> </PoliceReport>
>
> So the desired processing behavior is this:
>
> Read the next XML document.
> If the XML document contains data about cars then
>     Wait until the police report arrives ....
>     .......... time elapses ........... the police
>     report arrives: if it says the car is stolen
>     then output "stolen" else output ""
>
> I want to express that!
>
> And, I want to express it, not in an XSLT program, but in a single XPath
> expression!
>
> The UNIX shell has an analogous functionality that I describe now. The
> "trap" command can be added into a shell program. The command has this form:
>
>         trap command signal
>
> It has this meaning: During execution of the shell program, if 'signal' is
> received, then execute 'command'.
>
> Here's an example to illustrate how it may be used ('2' is the signal for
> the user pressing Ctrl+c; i.e., for the user terminating the program):
>
>         trap "rm WORKDIR/file; exit" 2
>
> That means: If the program is suddenly terminated (by the user pressing
> Ctrl+c), remove 'file' from the WORKDIR folder and then exit.
>
> I want that kind of functionality! In XPath!
>
> Is it possible to achieve that functionality using XPath? Or is this
> outside the realm of XPath capabilities?
>
> /Roger
>
> For my own notes:
>
> Potentially relevant information:
>
> Michael Kay Balisage paper: Asynchronous XSLT
>
>
> https://www.balisage.net/Proceedings/vol25/html/Kay01/BalisageVol25-Kay01.html
>
> Xalan-J Thread.sleep() function: all links I followed failed. Still
> available?
>
> Java Sleep() function:
> https://www.geeksforgeeks.org/thread-sleep-method-in-java-with-examples/