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Re: [xsl] Tree Comparing Algorithm

2020-02-03 14:10:10
Thanks both. Martin's solution sort of worked, but it only gave me 21
children, but I had around 21000 nodes in the xml. I am not sure to what
depth the comparison is happening.

On Mon, 3 Feb 2020 at 12:16, Michael Kay mike(_at_)saxonica(_dot_)com <
xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:

The only facility in the XSLT 3.0 to allow streaming of two input files
"in parallel" is xsl:merge, and as Martin points out, that's rather
specialised and not really suited to your requirements.

In Saxon, streaming is in most cases done in push mode (where the parser
owns the control loop, and sends events to the XSLT processor). You can't
have two parallel control loops except with multi-threading, so the
opportunities for streaming multiple files are limited (with xsl:merge,
Saxon indeed uses multi-threading).

At first sight, I don't see an XSLT-based answer to this one.

Except, perhaps: you could do a streamed transformation of each input
documents into an XML representation of an event stream, like

<startElement name="folder" path="" hash=""/>
<startElement name="folder" path="" hash=""/>
<endElement name="folder"/>


and then attempt to do an xsl:merge of the two event streams.

Michael Kay

On 3 Feb 2020, at 13:47, Vasu Chakkera vasucv(_at_)gmail(_dot_)com <
xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:

Hi All,
I am planning to write a XML Tree comparing XSLT using streaming.
The XML Trees look something like this
<root path="" mhash =" ">
  <folder path ="" mhash ="">
    <folder path ="" mhash ="">
       <leaf path ="" mhash ="">
There will be two such XML files to compare . These two XMLs are generated
before and after moving a folder from source to destination. Source and
destination could be two different OS.
This is essentially the serialized Merkle Tree output of a folder
structure. The idea is to run a Merkle Tree comparator that will pick the
nodes that did not match. Rules are as follows.

   1. If the root node in both the tree matches, then there is not
   difference in the entire tree(because of how the Merkle tree is generated)
   2. If root node hash does not match, we go to the child container and
   compare the hash of the child container in both the XML files. ( the XML
   folders structure will be identical with respect to the hash, but the
   folder  path may be different because of the linux, windows path
   conventions. Otherwise the folder structure is meant to be the same.)
   3. If the hash of a folder from both the trees are same, the entire
   tree under the folder that matches the hash is ignored.
   4. if the hash of a folder from both the trees are not the same, then
   the tree is further traversed and the step 3 is repeated.
   5. The XSLT keeps writing out the nodes that do not match the hashes
   in the source and target xml files

So at the end of the processing, A comparator tree should be serialized,
that has the nodes that have a non matching leaf node.
Looking at the serialized tree, we can determine, which files got messed
up while doing a transfer from Source to target.

I am able to do this using non streaming xslt, but with streaming, since
we need to stream two trees at a time and match compare the nodes,  i am
not very sure how to proceed.
I am able to do manipulations on one XML with streaming. I tried a few
tricks, but did not get anywhere ( I am not very comfortable copying my
code scribbling here)

I need streaming because the XML files may be big.
If someone has done something similar, or point me to an  intelligent way
to do this, I will be thankful.


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Vasu Chakkera
NodeLogic Limited
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