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Subject: Notes from XDI TC special meeting Friday 16 May 2008


I apologize for taking so long to post these notes from our XDI TC special
meeting on May 16 -- I was tied at two conferences last week.

ATTENDING IN PERSON

Nat Sakimura
Tatsuki Sakushima
Markus Sabadello
Drummond Reed

ATTENDING VIA TELECON

Bill Barnhill
Andy Dale
John Bradley


1) REPORT ON INTERNET IDENTITY WORKSHOP AND DATA SHARING SUMMIT

Nat, Tatsuki, Markus, Drummond, Kermit Snelson, Victor Grey, Gabe Wachob,
Andy Dale, and John Bradley all attended these events and held several
sessions on XDI. They were well attended and well received. There was
particularly strong interest in i-pages, the XDI-backed personal data
sharing service developed by Andy Dale, John Bradley, and Steve Churchill;
and in relationship cards (r-cards), the information card-based data sharing
service using XDI being developed by the Higgins Project. 


2) DISCUSSION OF RDF QUADS

At the Data Sharing Summit, there was discussion of RDF quads and their use
in the Linked Data model. Bill explained that some RDF practitioners are
using it for reification, and some are using it for subgraphs. It started as
Named Graphs and has now become part of SPARQL.


3) LINK CONTRACT REQUIREMENTS AND DESIGN IN THE ATI MODEL

Andy reported that there was consensus in discussions at IIW that link
contracts fall into two parts: the network enforceable part and the
non-network enforceable part.

* The network-enforceable half consists of operators on a set of XDI
references to data.
* The non-network enforceable half consists of policy that applies to the
first set, and must include a reference to the jurisdiction of the contract.

Andy explained that this differs from DRM in that it is not intended to be a
mechanism for enforcement of rights over digital objects, rather simply a
method for expression of the terms and conditions of a data sharing
relationship.

Andy and John went on to explain that in the XDI ATI model, access to data
in an authority's graph is always provided through a single root node in a
graph. You must find at that node a signed contract. The contents of that
contract is a signed and countersigned set of references to the data that is
governed by the contract.

ooTao's implementation of this brings only the "permissioned graph" into
memory. This is done by using a small number of queries or "pattern matching
rules" for data sets. These queries can use the XDI query operators.

The query language has been built out of three primitives: $all,
$descendants, and $children. In conjunction with the XRI delimiters, this
covers the way you crawl the tree.

Andy's and John's view is that it is critical that the protocol and data
model be very explicit about how that works so that permissioning is
unambiguous. Example: doing a $set on an address of a node that has two
links and a ref could have impacts beyond what is expected.

With regard to the non-network enforceable half, here the outer structure is
a container called $contracts that contains a $contract that contains a
$social.policy and $network.policy. The $social.policy contains the URL
where the document can be found together with a copy of the actual document.

Bill pointed out that anyone who has access to data under a contract must
have access to the contract itself.

Contracts can reference data in other contracts. 

3A) LINK CONTRACT SIGNATURES

In the XDI ATI model, Andy explained there are two forms of signatures: one
to a set of XRIs that cannot be changed without needing a new signature, one
to an identifier of a data set that can change.

The first authority (the provider of the contract) signs the contract and
then the other authority signs it. You can just have the requester's
signature, since the provider persists the contract. However countersigning
is necessary if the requester wants a copy. One option for doing that is
countersigning only when data is requested.

3B) LINK CONTRACT STRUCTURE

The ATI model uses the XRIs $link and $contract. An instance of $link will
contain an XRI to an authority - that's the other party to the contract. 

$link is linked to one or more $contracts.

The signed contract ends out covering XDI data on the $link node.

Andy suggested that we could use the policy work being done by Liberty.

3C) LINK CONTRACT NEGOTIATION 

Unfortunately Andy and John ran out of time to go over the negotiation
protocol that Andy, Steve, and John have developed and had to leave the
call. We agreed we'd like to do that in a future call.


4) LINK CONTRACTS IN THE XDI RDF MODEL

We next went over the link contract structure illustrated in the Link
Contract section on page 31 of the XDI RDF Model document:

	http://wiki.oasis-open.org/xdi/XdiRdfModel

Markus explained the basic pattern of using a link contract template defined
by the XDI subject originally developing the contract. This template is then
instantiated by an XDI subject wishing to enter into a contract by adding
the link contract XRI as a predicate. The object is a subcontext containing
the XDI subjects granted permission under the contract and the predicates
(operations) applying to each. The objects of these predicates are
subcontexts defining the XDI graph ranges to which these permissions apply.


5) NRI LINK CONTRACT USE CASE

Bill Barnhill had to leave the call at this point, so the final part of the
session was devoted to Drummond and Markus reviewing with Nat and Tatsuki
the link contract use case that NRI has for OpenID trusted data sharing:

	http://wiki.openid.net/Trusted_Data_Exchange

Since the NRI team has already identified the necessary link contract
elements in an XML schema, it was agreed that the XDI TC should undertake
the job of analyzing how this could be converted to an XDI RDF link contract
following the design pattern discussed here.

# MARKUS to do a first pass strawman proposal. (DONE -- see
http://lists.oasis-open.org/archives/xdi/200805/msg00039.html). 

# DRUMMOND to add this to the agenda for XDI TC calls in June. 



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