Re: Meta Data Handling

At 01:04 AM 3/18/97 -0800, Yaron Goland wrote:

Yaron gave some very good reasons why headers were not a good way to
handle metadata. He mentioned namespace collisions, processing load,
wasted bandwidth, etc. Despite understanding these problems, he
goes ahead and recommends that headers be used for dealing with
metadata in order to keep the model "light". He cites the example
of small pieces of information such as modification dates to
justify this decision.

I agree with Yaron to a limited extent. Handling *all* metadata as
resources is inappropriate. However, it is my considered technical
opinion that handling *all* metadata as headers is just as inappropriate
as handling *all* metadata as separate resources. Some descriptions,
such as Content-length, Last-modified, Content-type, ... are best
carried as headers. Other descriptions, such as detailed revision
histories, provenance tracking, and bibliographic descriptions, are
best carried as separate resources.

WEB-DAV needs a metadata architecture that accommodates both. Furthermore,
it is not that difficult. When we send resources (original or "metadata")
between clients and servers we can use MIME headers for the "light"
metadata about particular resources, while still allowing separate
metadata packages to carry descriptions that are too heavyweight for
headers. We can send those resources in multipart message bodies, and
can use message/external-body if we want the client to know of the
existence of some big package but don't want to clog the lines by actually
sending it.

If we can agree on an architecture that isn't all one way or the other,
then we can advance to more meaningful arguments, like just what new headers
(if any) we need to define, what packages (if any) we initially want to
support, how (or whether) their elements can be used in both contexts, and
how we can do queries on them.

It seems to me that to make progress, this group needs to agree on
a few simple points and stop arguing over them. Can we start by
agreeing on two things:

1) Neither headers or separate resources meet all the requirements on
   metadata in WEB-DAV, so we will need a combined solution.

2) All communications between clients and servers will take the form of
   MIME messages, and frequently those messages will be multipart/related?

The last seems uncontroversial to me, but then I have been accused of being
an optimist :-).  I hope that the former is also uncontroversial given
the last few messages on this list.

>In order to handle the assignment, modification, discovery, and removal
>of meta-data I propose adding three new methods - METAPOST, METAGET, and
>METADELETE.

Assuming we agree that some metadata is handled by headers and some by
separate resources, we can now discuss ways of editing it. For metadata
held as resources, the GET, DELETE, and PUT (or POST) methods should
suffice. For the smaller info carried as headers we may need methods such
as you describe. I think the essential functionality of METAGET is already
handled by the HEAD method. Something like METAPOST and METADELETE seems
necessary.

I'll skip detailed comments on the methods at this time, but there is one
I just can't let go without remarks:

>5	Link Attribute
>
>If META* is adopted then links become attributes. I propose they be
>defined as follows:
[...]
>I also
>propose removing the rule that either the source or destination must be
>equal to the Request-URI. This will enable annotation facilities.

I think that redefining existing parts of the HTTP spec, such as LINKs,
is beyond the bounds of this WG. Furthermore, annotations can be
handled under the existing constraints on LINKs.


Later,

Ron Daniel Jr.              voice:+1 505 665 0597
Advanced Computing Lab        fax:+1 505 665 4939
MS B287                     email:rdaniel@lanl.gov
Los Alamos National Lab      http://www.acl.lanl.gov/~rdaniel
Los Alamos, NM, USA, 87545

Received on Tuesday, 18 March 1997 14:09:00 UTC