Hi Sandhya,
<p>
I think ETP may not cut it. If you are thinking of having a web interface to make a XML Docbook. Although it may, but some heavy customization must be done. But I do suggest you look at Content Repository and its api. You may have to roll you own CMS app on top of CR.
<p>
As for the export once you have your data in the CR that is similar to Docbook. Its only a matter of making a 2 templates one for putting out a web page and another for putting out a Docbook XML that can be downloaded.
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If I will approach the problem I will probably do it this way:
<ul>
<li>Study the DTD of Docbook. And see how to make a Content Type in the CR. You may need to create several Content Types and linking them with one another by using the cr_items.parent_id.
<li>Create some forms to put in the data into your content types.
<li>Create an upload facility and parser to import an existing Docbook document into the CR's content types.
<li>Create a web template and probably a parser to get content out of the web. It would be nice to have the parser in XSLT since a lot should be available. Although I think XSLT support in aolserver or OpenACS is poor.
<li>Create a template/parser to get CR data back into Docbook format.
</ul>
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Also it would be great that once you have done it you will share the code with OpenACS. I think this should be a great addition to OpenACS.