W3C home > Mailing lists > Public > www-rdf-dspace@w3.org > June 2003

Re: Comments on Motivating problems

From: Kevin Smathers <kevin.smathers@hp.com>
Date: Tue, 17 Jun 2003 11:33:24 -0700
Message-ID: <3EEF5EF4.3060706@hp.com>
To: "Butler, Mark" <Mark_Butler@hplb.hpl.hp.com>
Cc: www-rdf-dspace <www-rdf-dspace@w3.org>
More changes for technologies.tex and simile.bib are attached.

Cheers,
-kls


Butler, Mark wrote:

>Hi Kevin
>
>I have incorporated your changes, except for this line:
>
>
>  
>
>>-----Original Message-----
>>From: Kevin Smathers [mailto:kevin.smathers@hp.com]
>>Sent: 17 June 2003 00:03
>>To: www-rdf-dspace
>>Subject: Comments on Motivating problems
>>
>>
>>Hi all,
>>
>>More to follow, but here are my first set of comments from a quick 
>>review of the current document status.
>>
>>
>>-- 
>>========================================================
>>   Kevin Smathers                kevin.smathers@hp.com    
>>   Hewlett-Packard               kevin@ank.com            
>>   Palo Alto Research Lab                                 
>>   1501 Page Mill Rd.            650-857-4477 work        
>>   M/S 1135                      650-852-8186 fax         
>>   Palo Alto, CA 94304           510-247-1031 home        
>>========================================================
>>use "Standard::Disclaimer";
>>carp("This message was printed on 100% recycled bits.");
>>
>>
>>    
>>


-- 
========================================================
   Kevin Smathers                kevin.smathers@hp.com    
   Hewlett-Packard               kevin@ank.com            
   Palo Alto Research Lab                                 
   1501 Page Mill Rd.            650-857-4477 work        
   M/S 1135                      650-852-8186 fax         
   Palo Alto, CA 94304           510-247-1031 home        
========================================================
use "Standard::Disclaimer";
carp("This message was printed on 100% recycled bits.");


? patch2.txt
? relevantTechnologies/foo
Index: simile.bib
===================================================================
RCS file: /cvs/simile/docs/simile.bib,v
retrieving revision 1.26
diff -u -r1.26 simile.bib
--- simile.bib	17 Jun 2003 13:32:55 -0000	1.26
+++ simile.bib	17 Jun 2003 18:31:34 -0000
@@ -796,3 +796,13 @@
 	organization="MIT", 
 	howpublished="\url{http://ocw.mit.edu}"}
 
+@MISC{shibboleth,
+        TITLE="{Shibboleth Initiative}",
+	organization="Internet2",
+	howpublished="\url{http://shibboleth.internet2.edu/shib-intro.html}"}
+
+@MISC{Damianou,
+        TITLE="{A Policy Framework for Management of Distributed Systems}",
+	author="Nicodemos Damianou",
+	organization="Imperial College's Policy Research Group",
+	howpublished="\url{http://www-dse.doc.ic.ac.uk/Research/policies/ponder/thesis-ncd.pdf}"}
Index: relevantTechnologies/technologies.tex
===================================================================
RCS file: /cvs/simile/docs/relevantTechnologies/technologies.tex,v
retrieving revision 1.3
diff -u -r1.3 technologies.tex
--- relevantTechnologies/technologies.tex	17 Jun 2003 13:33:09 -0000	1.3
+++ relevantTechnologies/technologies.tex	17 Jun 2003 18:31:34 -0000
@@ -496,7 +496,8 @@
 The other naming problem is when we are using URLs to describe documents
 and their subcomponents i.e. 
 identifying resources smaller than the atomic document.   
-Doing this with a URL is arguably convenient, in that it permanently 
+Doing this within a URL (according to some specification of the URL 
+semantics) is arguably convenient, in that it permanently 
 binds the smaller object to its containing object, giving you the 
 semantics that if you are looking for the smaller object it is a good 
 subgoal to look for the containing object.
@@ -515,53 +516,42 @@
 that depict violence, and remove them during playback of the movie.
 
 Obviously the metadata read by the DVD player will have to include
-data that identifies the parts of the overal movie that represent the
-selected content.  Using a URL to represent the content is insufficient
--- we can't create new URL's for every possible subregion of a movie, 
+data that identifies the parts of the overall movie that represent the
+selected content.  Using an opaque URL to represent the content is 
+insufficient -- we can't create new URL's for every possible subregion 
+of a movie, 
 and even if we did so, such an approach wouldn't help in finding an 
 playing back parts of the movie that do not correspond to that URL.
-
-Naming, as is being described in section 3.2.7, has nothing to do with
-the URL for the asset. The purpose of naming is to create a linkage
+The purpose of naming in this context is to create a linkage
 between the metadata and the movie subregion.
 
-Stepping out of our example, the purpose of Naming in this document
-is to represent other assets in ways that URLs cannot. Such linkages
-are neccessarily specific to the type of data being indexed so they
-cannot be generalized to a single technology, but that doesn't mean 
-that we can't create a pattern around them.
+Stepping out of our example, the purpose of Naming
+is to represent other assets in ways that opaque URLs cannot. Such linkages
+are semantically tied to the type of data that they index, so
+so they cannot be generalized to a single technology, but that doesn't mean 
+that we can't create a usage pattern around them.
 
 While using URLs with semantics is one option, an alternative way to
-specify a particular subpart of the movie is with a blob of RDF  eg,
-there is a resource foo (no semantics) and assertions
-"foo fragment-of the-lord-of-the-rings", "foo start-offset 300", and
-"foo end-offset 500".  Whatever semantics I intend to place in the URL, I
-can instead, without any loss of expressive power, place in a blob of
-RDF statements.  This leaves me with URLs containing no semantics at
-all, which has a consistency I like.  
-
-There are many different ways to represent the subgraph in question.  You
-have broken it up into three statements (and an implied statement of the
-schema type), another implementation might use more statements or fewer.
-In addition there are many other types of documents that could be named,
-in whole or in part.
-
-The point of the Naming discussion is to map those statements to their
-meaning, where the meaning is a subindex into a document.  This makes 
-Name a specialization of Class.
-
-The issue here is not so much whether or not URNs are appropriate for 
-each of the names, but rather:
-
-by what mechanism are the names generated and assigned?
-which of the URNs are URI's, and which are URL's?  How can I tell?
-\begin{itemize}
-\item Here "A" could be a URL, but if I wish it to be location-independent 
-I may assign a URN and use some mapping service (PURLs, Handles).
- "A" is a URL - do an http:get
-\item "B" is probably a URN, not useful to attempt to resolve it.
- I must map to some query on the contents of the graph represented by contents of "A".
-\item "C" could be either a URN or a URL.  How do I find the schema? Not sure
+specify a particular subpart of the movie is with an RDF subgraph.  Suppose
+there is a resource some-uri (no semantics) and assertions
+"some-uri fragment-of the-lord-of-the-rings", "some-uri start-offset 300", and
+"some-uri end-offset 500".  Whatever semantics I intend to place in the URL, I
+can instead, without any loss of expressive power, place in an
+RDF subgraph.  This leaves the URL free of semantics and thereby confers the 
+benefit of restricting semantic data to RDF as the solitary format.  
+
+Another issue here is by what mechanism are the names generated and assigned.
+Which of the URNs are URI's, and which are URL's, and how can I tell?
+\begin{itemize}
+\item Here some-uri could be a URL, but if I wish it to be location-independent 
+I may assign a URN and use some mapping service (PURLs, CNRI Handles).
+ If some-uri is a URL do an http GET to retrieve the metadata needed to
+ locate the subregion of film.
+\item The predicates fragment-of, start-offset, and end-offset are 
+probably  URN's, it is not useful to attempt to resolve them.
+ Collectively these predicates map to some query on the contents of the 
+ graph represented by contents of some-uri.
+\item The object the-lord-of-the-rings could be either a URN or a URL.  Either way there must be some means of discovering the schema or type by which the object together with the semantic subgraph should be interpreted.
 \end{itemize}
 
 \subsection{Processing Models}
@@ -613,7 +603,7 @@
 support automated discovery. 
 \end{itemize}
 
-It is possible to higlight this with some other processing models:
+It is possible to highlight this with some other processing models:
 
 \subsubsection{Resource directory discovery via namespace processing model}
 
@@ -780,7 +770,16 @@
 
 \subsection{Classification}
 
-One important issue is classification, but it has several different axes:
+One important issue is classification, that is the specification of
+the type of a referenced resource, and also of the role of that resource in
+the current context.  In RDF graphs the classification role of a
+resource is obtained from the predicate that links that resource
+to the current graph.  When the linked resource is itself an RDF
+graph then the type can be inferred from RDFS statements in the
+referenced graph.  When the linked resoruce is not an RDF graph there
+must be some other mechanism for describing type.  However, even
+when type is clearly specified, the classification of a resource
+has several different axes:
 
 \begin{description}
 \item [Metadata versus original versus abstract object] Classification
@@ -809,6 +808,12 @@
 \caption{\label{dissemninationdiagram}Dissemination}
 \end{figure}
 
+Dissemination implies a requirement for transformational repurposing
+of the data and metadata stored within the system.  A graph might be
+represented to a web browser using a directory metaphor, or it might 
+be transformed into embedded HTML to start a multimedia player to turn 
+MP3 data into sound.
+
 \subsection{To Humans}
 
 Current thinking is to have an ontology describing how metadata is
@@ -818,7 +823,63 @@
 
 \subsection{To software / agents}
 
-Policy-compliant dissemination 
+The most successful strategy for defining application to application 
+communication formats, permissions, and policies, has been application
+specific.  If a web site wants to share a service with another web site
+then the authors of the respective sites agree on a set of ad-hoc
+interfaces.  Web services standards such as SOAP and XML-RPC are starting
+to make a dent in these custom interfaces, but the policy and security
+implementations have remained the custom work of each service provider.
+
+\subsubsection{Security and Policy}
+
+One approach to a universal view of distributed security is to express
+permissions or policies in terms of split capabilities (see Alan Karp's 
+tech report).  By communicating in terms of these capabilities cooperating
+systems can enforce access controls that have been compiled from policies
+which they don't themselves understand.
+
+A more pressing issue is not how to implement access control in general, 
+but rather, how to express and enforce dynamic access control policies over 
+RDF graphs.
+
+Security must be tightly coupled with Simile's access policy and event 
+management mechanisms. That is, access policies, event mechanisms,
+and security must be interdependent. In particular Simile must define
+how one can use policies to restrict access to (RDF) subgraphs. For
+example, given a set of statement identifiers (e.g., reified statements),
+how could one use a domain expression to specify a subset of the set
+to be the target of a security policy? 
+
+By extension, Simile may need to express and enforce ``implied'' 
+policies. For example, a new statement
+being added to a store could cause a policy to now apply to existing
+statements. 
+
+Note that the question of how to express access policies
+for RDF is different from (and more interesting than) the question of
+how to express access control policies in RDF.  The latter is simply
+a presentation issue, and is common to all uses of RDF, while the former
+strikes at the heart of what security means as applied to RDF.
+
+Simile has not yet committed to a model for its security, or for that matter for its policy mechanisms. In particular, the following issues need to be explored in the context of Simile:
+
+\begin{itemize}
+\item How should we express policies over RDF subgraphs? (This seems a particularly rich area.)
+
+\item How can we enforce policies over RDF subgraphs? (This seems a particularly rich area.)
+\item What should be the granularity of access policies? (e.g., resource, subgraph, model?)
+\item What should be the scope of policies ? 
+\end{itemize}
+
+We all agreed that from Genesis's perspective, the granularity could be model-based. That is, that if Genesis provided a means of controlling access to a given model, then Simile could use it to implement its own finer-grained mechanisms.
+
+There are to two specific pieces of related work that are interesting:
+
+\begin{itemize}
+\item The first is A Policy Framework for Management of Distributed Systems \cit{Damianou}, the thesis of Nicodemos Damianou, whose advisor at Imperial College, University of London, is Morris Sloman (and who has also collaborated with Dr. Emil Lupu). Daminanou is a member of the Imperial College's Policy Research Group, which has proposed Ponder, an object-oriented, declarative, programming language for specifying distributed system management and security policies. The Policy Research Group also provides associated tools for editing, compiling and managing policies in a distributed system. (Note that Francisco Garcia from Agilent is a program co-chair for the upcoming IEEE workshop on Policies for Distributed Systems and Networks, where last summer's SEED Lalana Kagal has a paper.)
+\item Also of interest is the Internet2 Shibboleth initiative \cite{shibboleth}. The goal of Shibboleth is to develop an open, standards-based solution for organizations to exchange information about their users in a secure and privacy-preserving manner. 
+\end{itemize}
 
 \section{Distributed Resources}
 
@@ -991,12 +1052,15 @@
 For example it may hide the syntax used to express the schema, such as 
 RDFS or OWL from the user and instead present the schema graphically. 
 
+Codified best practices, whether in the form of processes or wizards,
+will go a long way toward making the schema system easy to use.
+
 \subsection{Simplify}
 
 Applying complex classification schemes on resources could negatively
 impact users' ability to search for resources. It
-is important to hide unnecessary detailS until userS need it. This
-may be done in several ways:
+is important to hide unnecessary details, and then to introduce complex
+operations gradually as users need it.  This may be done in several ways:
 
 \begin{itemize}
 \item By providing default behaviors that allow users to carry out typical
@@ -1016,7 +1080,7 @@
 for a user to repeat the same query multiple times on different systems. 
 \item It may be desirable to provide mechanism to allow users to update
 several records simultaneously as a set rather than individually when 
-performing instance versioning. 
+performing schema versioning. 
 \item If possible, tasks like merging of records or mapping between schemas
 and vocabularies should be automatic and only require user intervention
 when absolutely necessary. 
@@ -1039,17 +1103,29 @@
 other uses and then making recommendations based on the items other
 users have searched for. 
 
-There are some limitations with the current versions of such systems.
-Most notably they have no way for a user to denote the context for
-their search: therefore on Amazon a user may search for very different
+Such systems do have limitations.  Most notably it can be difficult to
+infer the context for a search: therefore on Amazon a user may search 
+for very different
 items if they are purchasing an item for a relative compared to when
-they are purchasing items for themselves. Therefore making recommendations
+they are purchasing items for themselves.  Making recommendations
 based on the entire users history may not be as effective as making
-recommendations based on recent search terms from the user. Also there
-are potential privacy issues that need to be addressed when recording
-user behavior, whether it is occurring with or without their knowledge. 
+recommendations based on recent search terms from the user.  
+
+Also when combining user behaviors into groups it is important for
+many applications to protect privacy.  When recording
+user behavior, whether it is occurring with or without their knowledge,
+the system must be able to remove any personally identifying information
+from the collective behavior predictors.
+
+Other factors include whether to have users self-categorize, or to
+infer categorization from a best fit of behavior.  There must also be 
+mechanisms for defining and refining these categories.
 
 \subsection{Policy Expression}
+
+In user interfaces policy expressions need to be translated into human
+readable text that simply and concisely informs the users of their 
+rights and limitations with respect to accessed data.
 
 \subsection{Misc}
 
Received on Tuesday, 17 June 2003 14:34:19 EDT

This archive was generated by hypermail pre-2.1.9 : Wednesday, 24 September 2003 13:35:24 EDT