[boost] [Serialization] Some ideas for XML

From: Jared McIntyre (jmcintyre_at_[hidden])
Date: 2006-06-22 17:44:03

I've been using serialization to XML for a while now. Its worked very well for what I originally needed. However, a 
number of requests have come my way for enhancements to our system based on the concept that the file is XML, but they 
aren't really possible under the existing framework.

The first item involves style sheets (and potentially other similar tags). Currently there is no way to insert 
<?xml-stylesheet type="text/xsl" href="file.xslt" ?> into the file from code. And if I do it manually, serializer 
won't be able to load the file. Is there any interest out there in this kind of functionality (adding tags like this 
from code, and ignoring such tags on load)? If so, could someone point me to where to look in the code to put together 
a prototype?

The second thing is a concept that conflicts with the existing versioning scheme. I'm asked regularly why the 
deserializer cares if there are tags in the file that it doesn't know about (most people assume these will be 
ignored). The reason they want this is they want a newer version of the code to add a few tags to the file, but the 
older version continue to read the file while skipping those new items. For example, the original version of a class 
would be:

<shirt class_id="5" tracking_level="0" version="0">
        <color>red</color>
        <size>large</size>
</shirt>

and the second version would be

<shirt class_id="5" tracking_level="0" version="1">
        <color>red</color>
        <size>large</size>
        <material>cotton</material>
</shirt>

Their thinking is that if the old code loads the file, it should just ignore the <material> tag and load happily. 
 However, in order of the new code to read the old file, the version has to be revved to 1 so that it knows to add a 
<material> value on load. In doing that version rev, even if it could ignore the <material> tag, the old code would 
see that version 1 and assume it didn't know how to load it. Can anyone think of a way around this short of changing 
the version scheme, which doesn't seem like an option.

Thanks,

Jared McIntyre