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a Grand Unified Locking Proposal (GULP, or perhaps, GULP! :-)

From: Geoffrey M. Clemm <geoffrey.clemm@rational.com>
Date: Wed, 12 Jan 2000 18:12:43 -0500
Message-Id: <10001122312.AA22058@tantalum>
To: w3c-dist-auth@w3.org

Eric suggests that a URL-based locking model should be mapped into the
underlying collection resources that implement the namespace.  I agree
with both this conclusion and the reasoning leading up to it.

But I think it is simpler to model namespace protection and state
protection as being two results of a single kind of lock, as opposed
to the result of two different kinds of locks.  This avoids the
problem of describing how namespace locks and state locks interact.

In an attempt to make the proposal both understandable and complete,
I've broken it into two parts.  The first part is a series of bullets,
which largely correspond to the "URL-based locking" proposal I mailed out
a while ago.  The second part is the same series of bullets fleshed out
with a more formal description of each bullet in terms of an underlying
resource model and effects on the visible lock state of resources.

**************************

GULP: Part I

- A URL identifies a resource.
- A LOCK request creates a lock on the request URL.
- An UNLOCK request removes all locks with the specified lock token.
- A lock on a URL protects which resource is identified by that URL.
- A Depth:N lock on a URL locks any URL that extends the locked URL by no
more than N segments.
- A Depth:infinity lock on a URL locks all URL's that extend the locked URL.
- If an exclusive lock identifies a resource, no other lock of that type can
identify that resource.
- A write-lock on a URL protects the body and dead properties of any
resource identified by that URL.

**************************

GULP: Part II

- A URL identifies a resource.

The URL "/" identifies a resource. A collection contains a set of bindings,
where a binding is a mapping from a URL segment to a resource. If "/path"
identifies a collection C, and C contains a binding that maps the segment
"x" to resource R, then the URL "/path/x" identifies resource R.

- A lock is on a URL. Every lock has a lock token and a lock owner.

Every lock on a resource has a name which is a relative URL (i.e. a slash
separated sequence of URL segments). Every LOCK request that succeeds
results in a new globally unique lock token. Every lock token has an owner
that is the principal of the LOCK request.

- A LOCK request creates a lock on the request URL.

When a request of the form "LOCK /pathX" succeeds, a lock named "pathY/."
with a new lock token is added to the resource identified by "/", where
"pathY" is the result of applying standard URL path transformations to
remove all segments named "." or ".." from "pathX". If a collection C has a
binding from "segX" to resource R, and a request adds a lock named
"segX/pathZ" with token "L" to C, then the request adds a lock named "pathZ"
with token "L" to R. Similarly, if a collection C has a lock named
"segX/pathZ" with token "L", and a request (e.g. PUT, COPY, MOVE, BIND) adds
a binding in C from "segX" to resource R, then the request adds a lock named
"pathZ" with token "L" to R. If the attempt to add the lock named "pathZ" to
R fails, the request MUST fail.

- An UNLOCK request removes all locks with the specified lock token.

When a request of the form "UNLOCK /pathX; Lock-Token L" succeeds, then the
lock with token "L" is removed from the resource identified by "/". If a
collection C has a binding from "segX" to resource R, and a request removes
a lock named "segX/pathZ" with token "L" from C, then the request removes a
lock named "pathZ" with token "L" from R. Similarly, if a collection has a
lock named "segX/pathZ" with token "L", and a request (e.g. DELETE, MOVE)
removes a binding in C from "segX" to resource R, then a lock named "pathZ"
with token "L" is removed from R.

- A lock on a URL protects which resource is identified by that URL.

If a collection identified by the URL "/colX" contains a lock named "pathZ"
with token "L", if a request would change the resource identified by
"/colX/pathZ", the request MUST specify token "L" in an IF header and the
request principal MUST be the owner of token "L".

- A Depth:N lock on a URL locks any URL that extends the locked URL by no
more than N segments.

If a collection C has a binding to resource R, and a request adds a Depth:N
lock named "." with token "L" to C, then the request adds a Depth:N-1 lock
named "." with token "L" to R. Similarly, if a collection C has a Depth:N
lock named "." with token "L", and a request adds a binding in C to resource
R, then the request adds a Depth:N-1 lock named "." with token "L" to R. If
the attempt to add the lock named "." to R fails, the request MUST fail.
Conversely, the Depth:N-1 lock is removed from R whenever a binding to R or
the Depth:N lock is removed from C.

- A Depth:infinity lock on a URL locks all URL's that extend the locked URL.

If a collection C has a binding to resource R, and a request adds a
Depth:infinity lock named "." with token "L" to C, and this is the first
Depth:infinity lock named "." with token "L" on C, then the request adds a
Depth:infinity lock named "." with token "L" to R. Similarly, if a
collection C has a Depth:infinity lock named "." with token "L", and a
request adds a binding in C to resource R, then the request adds a
Depth:infinity lock named "." with token "L" to R. If the attempt to add the
lock named "." to R fails, the request MUST fail. If a collection C has a
binding to resource R, and a request removes the last Depth:infinity lock
named "." with token "L" from C, then the request removes a Depth:infinity
lock named "." with token "L" from R. Similarly, if a collection has a
Depth:infinity lock named "." with token "L", and a request removes a
binding in C to resource R, then a Depth:infinity lock named "." with token
"L" is removed from R. Note that multiple Depth:infinity locks named "."
with the same token can be placed on the same resource due to multiple
bindings to that resource in a Depth:infinity locked collection.

- If an exclusive lock identifies a resource, no other lock of that type can
identify that resource.

If a request attempts to add a lock named "pathZ" with token "L" and type T
to resource R, and R already has an exclusive lock named "pathZ" with type
"L" but with a different token, the request MUST fail. Similarly, if a
request attempts to add an exclusive lock named "pathZ" with token "L" and
type T to resource R, and R already has a lock named "pathZ" with type T but
with a different token, the request MUST fail.

- A write-lock on a URL protects the body and dead properties of any
resource identified by that URL.

If a resource has a write lock named "." with token "L", in order to modify
the body or dead properties of that resource, a request MUST specify token
"L" in an IF header and the request principal must be the principal that
created the lock.

**************************

OK, Jason, Yaron, Eric, et. al, what did I forget this time? (:-)

Cheers,
Geoff
Received on Wednesday, 12 January 2000 18:12:49 GMT

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