Excess URI schemes considered harmful

I note, for includion in a future version of
http://www.ietf.org/rfc/rfc2718.txt that there is a very high cost
associated with the deployment of new URI schemes. There a number of
flexibility points in web architecture, and
those such as  Content-Type, and XML Namespace creation have a much lower
cost.  The Web depends on a very high shared knowledge of the properties of
URI schemes. New ones should only be introduced is absolutely necessary.

Content-Types should be defined by URIs, as are XML Namespaces. These then
leverage the existing URI schemes to anchor thier meanings in the web. This
allows anyone to make a local private Content-Type or namespace for their
own use. This does NOT apply to URI schemes.  The process has to be rooted
somewhere, and that root is the URI spec and the *small* set of  URI
schemes.

I would recommend that this be emphasized.  Specific examples of the
creation of  arbitrary trivial schemes such as the "webdav:" have violated
this rule in the past.

Tim Berners-Lee
http://www.w3.org/People/Berners-Lee