Hi!
I would like to contribute to Xindice and especially I would like to
contribute a two resolvers that implement versioning, like CVS, but
for XML/XIndice.
I am pretty new to Java and I wonder if I can get some pointers on how
to implement this and where to start.
Here is my first thoughts on how I want to implement things. I would
find it great if I can get pointers by some of you guys what you think
about it.
To enable versioning on a database the following configuration will be used:
<xindice>
<root-collection dbroot="./db/" name="db">
<queryengine>
<resolver autoindex="false" versioning-collection="version"
class="org.apache.xindice.core.query.XPathVersionedQueryResolver" />
<resolver versioning-collection="version"
class="org.apache.xindice.core.xupdate.XUpdateVersionedQueryResolver"
/>
</queryengine>
</root-collection>
</xindice>
Upon initialization the system will create the versioning collection
specified by the "versioning-collection" attribute, this collection
then only stores versioning information.
The _version_-collection then holds all information needed to extract
different revisions and versions from the database, while the db
(root-collection) actually just is unchanged, it's a view of
HEAD/TRUNK.
When a client queries something from the versioned collection
XPathVersionedQueryResolver add attributes to the result including
revision and branch information (something like
version:info="HEAD:1.43").
When a client updates the a versioned collection the
XUpdateVersionedQueryResolver saves the XUpdate snippet in the
versioning-collection.
When a client wants to get an old revision the
XPathVersionedQueryResolver just "combines" all xupdate-snippets from
the versioning-collection and returns a document, I would want to use
a special hierarchy in the versioning collection to enable to just use
XPath to get different versions:
(Of course this is not the final design, I have not even started
coding, but I would like to start a discussion about this)
Consider a collection "db" with an attached versioning collection
called "version", the db-collection initially contains:
<product>
<name>My Product</name>
<price currency="USD">32.00</price>
</product>
while the version collection contains (abbreviated for readability):
<branch name="HEAD">
<revision rev="1.1">
<info>
<comment>Initial version</comment>
</info>
<data>
<product>
<name>My Product</name>
<price currency="USD">32.00</price>
</product>
</data>
</revision>
</branch>
When the client changes the price from 32.00 to let's say 30.00, the
version collection contains (abbreviated for readability):
<branch name="HEAD">
<revision rev="1.1">
<info>
<comment>Initial version</comment>
</info>
<data>
<product>
<name>My Product</name>
<price currency="USD">32.00</price>
</product>
</data>
</revision>
<revision rev="1.2">
<info>
<comment>Change price</comment>
</info>
<data>
<xupdate:update select="/product[1]/price">
30.00
</xupdate:update>
</data>
</revision>
</branch>
To get a get a special version of a document, one would use the
following XPath expression:
/product[1]/[EMAIL PROTECTED]'HEAD']/[EMAIL PROTECTED]'1.2']/complete
(I have not yet really figured out a XPath format)
As you can see the complete tag does not really exist in the database,
but it should be generated on-the-fly by combining all preceding
revisions.
Likewise the XPath expression:
/product[1]/[EMAIL PROTECTED]'HEAD']/[EMAIL PROTECTED]'1.2']/diff/[EMAIL
PROTECTED]"HEAD"]/[EMAIL PROTECTED]'1.1']
Would generate a xml with the differences between HEAD 1.1 and HEAD
1.2 of /product[1].
I wouldn't want this email to become very long, so I will just stop
here, I do really look forward to your opinions though.
Regards,
Mikael Olenfalk
