Re: sub-tree filtering proposals

[Phil Shafer <phil@juniper.net>]

"Glenn Waters" writes:
>It's not pointless. Some reasons that an XPath subset is useful are:
>- compatability with full XPath which allows developers to learn one
>set of filtering

... and then be fustrated when the full xpath doesn't work....

>- a clean migration path from "XPath-lite" to "XPath-full"

I don't see this happening.  If you start with a subset and
grow it over time, clients will never know what subset the
device supports and will break on devices that don't match
their requirements.  Given that high-end devices are likely
to just pick up a full implementation (libxml2), the subset
will be broken day one.  Even then, the ability of the
device to implement arbitrary bits of XPath logic and
expressions will be an immense and changing burden.  Unless
we're all switching over to XML databases on the device,
the act of doing something like:

   following-sibling::security-associations[preceding-sibling::sa-tunnel-information[1]/sa-tunnel-index=$xpath-tunnel-number]

won't be simple.

Thanks,
 Phil

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