XML & memory use/releas

[Martin Blackman]

Thanks a lot for that Jan, that may be the way for me to go.
The prettyprint stack is nice, by the way, and I'm sure you're aware
but for the benefit of any newbies the stack can be sped up a lot by
putting everything into a global variable first before putting it into
the field at the end.

regards
Martin

On 27/01/07, Jan Schenkel <janschenkel at yahoo.com> wrote:
> --- Martin Blackman <martinblackman at gmail.com> wrote:
> > Dear listfolks,
> >
> > I've noticed that creating an xml tree from a file
> > using
> > 'revcreatexmltree' can take up anything from 15 to
> > 30 times the size
> > of the file on disk in memory.  Does that sound like
> > Rev is doing
> > anything peculiar to those with more understanding
> > of the underlying
> > behaviour ?
> >
> > I need to deal with some reasonably large files and
> > so need to
> > consider ways to avoid changing the user's computer
> > into treacle. (
> > I've been able to grind my 512MB laptop practically
> > to standstill but
> > my desktop seems to manage OK even when its physical
> > memory available
> > is very low)
> >
> > [snip]
> >
> > Any thoughts ?
> > Many thanks
> > Martin Blackman
> >
>
> Hi Martin,
>
> If you're handling huge XML files and don't actually
> need to manipulate the data in the DOM tree (Document
> Object Model), you could use the SAX approach (Simple
> API for XML).
> Rather than going through the entire file and building
> up a huge tree structure in memory, SAX parsers send
> messages as they traverse the XML text. Messages are
> sent at the start and end of the parsing process, as
> well as at the start abnd end of a tag, and the
> element data.
> So if you're just pulling information out of an XML
> file, SAX parsers can save you a lot of memory.
>
> In Revolution, you'll use a variation on the
> 'revCreateXMLTreeFromFile' function and trap the
> 'revXMLStartTree', 'revStartXMLNode',
> 'revStartXMLData', 'revEndXMLNode' and 'revXMLEndTree'
> messages.
> See the dictionary for more information on the
> peculiarities of these messages. In a nutshell, when
> you pass 'true' as the final parameter of the
> 'revCreateXMLTreeFromFile' function, the above
> collection of messages will be sent to the current
> card as it parses the XML structure.
>
> I recently made a little stack that uses this approach
> to 'pretty print' XML files that were produced by
> another app and weren't meant for human consumption.
> You can download this as a sample stack at the
> following URL:
> <http://www.quartam.com/tutorials/xmlprettyprint.rev>
>
> For those who just want the script, here's what I put
> in the card script:
> ##
> on PrettyPrint pFilePath
>  get
> revCreateXMLTreeFromFile(pFilePath,false,false,true)
> end PrettyPrint
>
> on DisplayStatus pStatus
>  put pStatus into field "fCurrentMessage"
> end DisplayStatus
>
> --
>
> local sCurrentDepth
>
> on revXMLStartTree
>  DisplayStatus "revXMLStartTree"
>  put "<?xml version='1.0'?>" into field
> "fPrettyPrint"
>  put 0 into sCurrentDepth
> end revXMLStartTree
>
> on revXMLEndTree
>  DisplayStatus "revXMLEndTree"
>  set the clipboardData["text"] to field
> "fPrettyPrint"
>  answer "Done..."
> end revXMLEndTree
>
> on revStartXMLNode pNodeName, pAttributes
>  DisplayStatus "revStartXMLNode" && pNodeName
>  add 1 to sCurrentDepth
>  if char -1 of field "fPrettyPrint" is not return
>  then put return after field "fPrettyPrint"
>  repeat with i = 2 to sCurrentDepth
>    put "  " after field "fPrettyPrint"
>  end repeat
>  put "<" & pNodeName after field "fPrettyPrint"
>  repeat for each line tAttributeKVP in pAttributes
>    put space & item 1 of tAttributeKVP & "=" after
> field "fPrettyPrint"
>    put quote & item 2 to -1 of tAttributeKVP & quote
> after field "fPrettyPrint"
>  end repeat
>  put ">" & return after field "fPrettyPrint"
> end revStartXMLNode
>
> on revEndXMLNode pNodeName
>  DisplayStatus "revEndXMLNode" && pNodeName
>
>  then put return after field "fPrettyPrint"
>  repeat with i = 2 to sCurrentDepth
>    put "  " after field "fPrettyPrint"
>  end repeat
>  put "</" & pNodeName & ">" after field
> "fPrettyPrint"
>  subtract 1 from sCurrentDepth
> end revEndXMLNode
>
> on revStartXMLData pElementData
>  DisplayStatus "revStartXMLData" && pElementData
>  put word 1 to -1 of pElementData after field
> "fPrettyPrint"
> end revStartXMLData
> ##
>
> Hope this helped,
>
> Jan Schenkel.
>
> Quartam Reports for Revolution
> <http://www.quartam.com>
>
> =====
> "As we grow older, we grow both wiser and more foolish at the same time."  (La Rochefoucauld)
>
>
>
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