Re: [xsl] Tree Comparing Algorithm

Subject: Re: [xsl] Tree Comparing Algorithm
From: "Dimitre Novatchev dnovatchev@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Tue, 4 Feb 2020 03:44:00 -0000
>  If the hash of a folder from both the trees are same, the entire tree
under the folder that matches the hash is ignored

Just a minor note that has nothing to do with XSLT:

It is not sufficient that two objects have the same hash code for them to
be considered "equal". When the hash codes are different this means that
the two objects are not "equal", however the equality of the hash codes
doesn't automatically mean the objects should be "equal"

Even if the probability of two objects to have the same hash code is low,
we should take this into account -- for example, we may choose to calculate
a pair of hash codes for each object, using two independent hashing


On Mon, Feb 3, 2020 at 5:46 AM Vasu Chakkera vasucv@xxxxxxxxx <
xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> 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 ="">
>        </leaf>
>     </folder>
>   </folder>
> </root>
> 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.
> Vasu
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