# A Formalism [Was: URN various ]

Daniel W. Connolly (connolly@hal.com)
Wed, 18 May 1994 15:53:46 -0500

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Owner: URN -> Principal
Owner-Name: URN -> Path

The owner namespace and the owner-local namespace are hierarchical:

Pricipal-Parent: Principal -> Principal u {}
Path-Parent: Path -> Path u {}

The relationship between URNs and Entities (i.e. typed bytestrings)
is NOT a function: the same URN may relate to different Entities
under different circumstances. Hmmm... perhaps it's useful
to say that at a given time, a resource has some set of
representative entities, i.e.:

Represent : Resource x Time -> SET(Entitiy)

Then, given a URN n and a time t, we can test whether a given
entity e is a representation of the named resource, by asking whether

e in Represent(Identify(n), t)

This is the sort of thing that can be represented by authentication
certificates (digital signatures). For example, we can write:

AssertRepr(md5(...), urn:davenport/docbook.dtd/1.1,
1994-05-23-10:45:23Z)

to mean

"The octets ... represent urn:davenport/docbook.dtd/1.1
as of 1994-05-23-10:45:23Z"

And take as an axiom that if
owner says AssertRepr(entity, urn:owner:name, time)
then
entity in Represent(Indentify(owner, name), time)

(b.t.w. P says S is a primitive in authentication formalisms.
See, for example,

*************** SRC Research Report #39
Date: February 28, 1989

"A Logic of Authentication."
Michael Burrows, Martin Abadi, and Roger Needham.
48 pages.
ftp://gatekeeper.pa.dec.com/pub/../.2/DEC/SRC/research-reports/SRC-039.ps.Z

for details)

For caching purposes, the times can be generalized to intervals
of time (ala Last-Modified: thru Expires:), or probabability
distributions around a given time (i.e. given e is ok at time t0,
the probability that e is right at time t1 is a function of t1-t0).

Whew! Finally... it all makes sense. Now... to write this up
and ad it to my research notbook...

Dan

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