OASIS eXtensible Access Control Markup Language (XACML) TC

I am finding the Hierarchical profile ambiguous and inconsistent and 
therefore incomprehensible, which may, similarly to the Multi-Resource 
profile be because there are essential contextual paradigms missing from 
the specification.

For the Multi-Resource profile, the missing contextual paradigms included:

    * It is necessary to pre-process the multi-resource request and
      submit individual requests to the PDP, and then to package up the
      responses into a single response.
    * The PDP, itself, can only process Request elements that in 2.0
      contain a single Resource element, single Action element, single
      Environment element, and multiple Subject elements, but each
      Subject element has to have a distinct SubjectCategory attribute,
      and in 3.0 there can be multiple Attributes elements, but each has
      to have a distinct Category attribute.

Once the above paradigms are established, the Multi-Resource profiles 
become comprehensible.

I suspect something similar is going on w the Hierarchical profile also.

Here is the background on the Hierarchical profile that I am trying to 
work thru (each bullet represents a potential issue to resolve or 
suggestion for improvement):

    * There needs to be a definition of "hierarchy". In particular, a
      "hierarchy" defn should state that the fundamental properties are
      that there must be a single root node with no parent, and that
      every other node in the hierarchy must have one and only one
      parent, and can have zero, one, or more children.
    * Section 3.2 is the biggest problem. To begin, the following needs
      confirmation: it appears that the key structural sentence for 3.2
      that explains what the four bullets that follow it are is lines
      314-315 (which is sandwiched between a negative statement on
      ResourceContent and subsequent 3 sentence "note") that state:
          o "The request context 

On Jan 14, 2009, at 10:54 PM, Rich.Levinson wrote:

>    * There needs to be a definition of "hierarchy". In particular, a
>      "hierarchy" defn should state that the fundamental properties are
>      that there must be a single root node with no parent, and that
>      every other node in the hierarchy must have one and only one
>      parent, and can have zero, one, or more children.

I am not sure why do you think this is a requirement.   It is a  
normal use case to inherit policy from more then one parent, and  
"ancestors" attribute approach allows such models without undue  
restrictions.

>    in order to submit a request  one has to somehow identify all  
> the hierarchies the given node
>      belongs to, all the hierarchies the node's parent(s) and  
> ancestors to, and include an Attribute element for each.

And why is that a problem?   Yes, if one wants "inheritance", graph  
needs to be defined, and attributes is a natural way to define it.

>  I suspect that at most one would need to collect all the normative  
> representations of only the resource-id node (i.e. identify all the  
> hierarchies it belongs to), then for each hierarchy, one would  
> evaluate the policies that apply to that hierarchy.
>

Policy evaluation does not need to know anything about hierarchies  
that are represented with an "ancestor" attribute.

Daniel;

  
  


Hi Daniel,


Thanks for the feedback. Let me try to clarify a bit.

My first objective is to understand what the spec currently says, and I
am finding that the terminology is inherently ambiguous, and as a
result, to me at least, that makes the details of the spec impossible
to understand. So, what I did was try to disambiguate by defining
"hierarchy". Let me be more explicit:


Lines 73-77 state the following:

In this Profile, a resource organized as a hierarchy may be
a “tree” (a hierarchy with a single root) or a “forest” (a hierarchy
with multiple roots), but the hierarchy may not have cycles. Another
term for these two types of hierarchy is “Directed Acyclic Graph” or
“DAG”. All such resources are called hierarchical resources in this
Profile. An XML document is always structured as a “tree”. Other types
of hierarchical resources, such as files in a file system that supports
links, may be structured as “forests”.


This is an inherently self-contradictory definition. A hierarchy has a
single root. It is an "ordered set", where each entity in the set has a
defined relationship to every other entity. A "forest" is not a
hierarchy. It is multiple hierarchies. The "definition" above is not
meaningful because it equates the singular and plural.


As a result of this self-contradiction, the spec then goes to introduce
what, to me are meaningless concepts, such as lines 315-316:

Note that a node in a hierarchical resource that is not
represented as an XML document MAY have multiple parents.


Therefore, in order to understand what the spec says, I first found it
necessary to come up with an unambiguous term for "hierarchy", which
allows sentences such as the above to be restated in a "meaningful"
way, such as:

Note that a node in a hierarchical resource that is not
represented as an XML document MAY belong to multiple hierarchies
and have a parent associated with each one.


I am not saying anything so far is "wrong", simply that it is not
understandable without firming up the definitions.


wrt to the "somehow identify all the hierarchies a node belongs to"
comment, I was not saying it was a problem, but simply observing that
that was what the spec was saying in terms of specific defn of the term
"hierarchy".


Finally, I do not understand your comment that says:

Policy evaluation does not need to know anything about
hierarchies that are represented with an "ancestor" attribute.


I am trying to understand what policies are supposed to do with the
definitions in the spec. i.e. it is the spec that says in section 3.2
that all the parent and ancestor nodes need to be assembled in the
request context. What "policy evaluation" are you referring to? Are you
saying what I indicated in original email that a policy does not need
to know anything about hierarchies that the resource-id node does not
belong to?


    Thanks,

    Rich




Daniel Engovatov wrote:
1448A6CC-1532-40B4-BFC0-DC9D0413097E@streamdynamics.com" type="cite">

On Jan 14, 2009, at 10:54 PM, Rich.Levinson wrote:


  
   * There needs to be a definition of
"hierarchy". In particular, a

     "hierarchy" defn should state that the fundamental properties are

     that there must be a single root node with no parent, and that

     every other node in the hierarchy must have one and only one

     parent, and can have zero, one, or more children.

  


I am not sure why do you think this is a requirement.   It is a normal
use case to inherit policy from more then one parent, and "ancestors"
attribute approach allows such models without undue restrictions.


  
   in order to submit a request  one has to
somehow identify all the hierarchies the given node

     belongs to, all the hierarchies the node's parent(s) and ancestors
to, and include an Attribute element for each.

  


And why is that a problem?   Yes, if one wants "inheritance", graph
needs to be defined, and attributes is a natural way to define it.


  
 I suspect that at most one would need to
collect all the normative representations of only the resource-id node
(i.e. identify all the hierarchies it belongs to), then for each
hierarchy, one would evaluate the policies that apply to that
hierarchy.


  


Policy evaluation does not need to know anything about hierarchies that
are represented with an "ancestor" attribute.


Daniel;


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Rich.Levinson wrote:
> I am trying to understand what policies are supposed to do with the 
> definitions in the spec. i.e. it is the spec that says in section 3.2 
> that all the parent and ancestor nodes need to be assembled in the 
> request context. What "policy evaluation" are you referring to? Are 
> you saying what I indicated in original email that a policy does not 
> need to know anything about hierarchies that the resource-id node does 
> not belong to?

Hi Rich,

I don't understand all the questions you have, but here's the basic 
approach of the profile in a simple example.

Assume the following simple hierarchy:

A <- B <- C

If someone requests access to C, the request will contain these 
attributes. this is from the top of my head, so it might be slightly 
inaccurate and I might have forgotten some of the attributes, but 
hopefully you get the idea.



All these attributes are there so it is possible to write policies which 
apply to parts of the hierarchy, not just individual nodes.

For example:



Matches only the resource C, nothing else.




matches the immediate children of B. In the example this is C, but if C 
had a sibling, it would also match.





Matches B or any node below B. In this case also C.

Best regards,
Erik

  


Hi Erik,


Thanks for this feedback. Unfortunately I did not have time to process
this email before today's meeting, but now that I have, it addresses
one of my major concerns which was the motivational context. i.e. by
seeing the actual example you provided, I can see that a Policy can now
base decisions knowing that some node happens to be an ancestor of the
requested node.


In addition, for your example, I think it would be instructive to show
when a node belongs to two or more hierarchies, that the collection of
attributes should probably have a mechanism to indicate which hierarchy
a node belongs to. For example, if C had an alias C', and parent B' and
ancestors A'->D' where, while (C = C'), that in general (B != B')
and (A != A') and obviously D' has no relation to the unprimed nodes at
all. We would then have a request:

<Resource>

 resource-id = C

 parent-id = B

 self-or-ancestor = C

 self-or-ancestor = B

 self-or-ancestor = A

 resource-id = C'

 parent-id = B'

 self-or-ancestor = C'

 self-or-ancestor = B'

 self-or-ancestor = A'

 self-or-ancestor = D'

</Resource>


It would seem to me that there needs to be a mechanism whereby one
would be able to tell the primed from unprimed attributes. Possibly
using Issuer


In any event, it is useful information to have this additional context
for understanding the current spec.


As agreed at the meeting, I will try to find some cycles to say what I
think needs to be done to make the spec easier to understand, which is
possibly just including the above information (i.e. your email extended
to multiple hierarchies with some example policy concepts, also such as
you provided).


Also, I think, as I mentioned at the end of the meeting that "scope"
may also have a meaningful role to include in this profile as well.
i.e. one can easily see that if policies are defined whereby certain
conditions apply when a resource-id node is within scope (as defined by
multi-resource spec) of some other node, that some if that ""other
node" happens to be a parent or ancestor of the resource-id node, then
those "certain conditions" would apply to the current resource-id being
requested.


    Thanks,

    Rich






Erik Rissanen wrote:
496F4DC8.4030200@axiomatics.com" type="cite">Rich.Levinson
wrote:

  
I am trying to understand what policies are
supposed to do with the definitions in the spec. i.e. it is the spec
that says in section 3.2 that all the parent and ancestor nodes need to
be assembled in the request context. What "policy evaluation" are you
referring to? Are you saying what I indicated in original email that a
policy does not need to know anything about hierarchies that the
resource-id node does not belong to?

  


Hi Rich,


I don't understand all the questions you have, but here's the basic
approach of the profile in a simple example.


Assume the following simple hierarchy:


A <- B <- C


If someone requests access to C, the request will contain these
attributes. this is from the top of my head, so it might be slightly
inaccurate and I might have forgotten some of the attributes, but
hopefully you get the idea.


<Resource>

 resource-id = C

 parent-id = B

 self-or-ancestor = C

 self-or-ancestor = B

 self-or-ancestor = A

</Resource>


All these attributes are there so it is possible to write policies
which apply to parts of the hierarchy, not just individual nodes.


For example:


<Target>

 resource-id = C

</Target>


Matches only the resource C, nothing else.



<Target>

 parent-id = B

</Target>


matches the immediate children of B. In the example this is C, but if C
had a sibling, it would also match.




<Target>

 ancestor-or-self = B

</Target>


Matches B or any node below B. In this case also C.


Best regards,

Erik

  
  


Hi All,


I am choosing this point (in the email threads) to continue discussion
of the issues with the Hierarchical profile as I think it contains the
best context to start from.


As indicated in the last couple of TC meetings, the update I proposed:

http://lists.oasis-open.org/archives/xacml/200901/msg00079.html


only goes part-way to addressing the problems I have found in the
Hierarchical profile specification. The update only includes
effectively a glossary with definitions of the terms that are currently
used in the spec that make the rest of the spec comprehensible (at
least from my perspective), and based on that glossary, the spec
includes a few clarifying edits, which are primarily intended to make
the statements in the spec consistent in terms of the definitions in
the glossary.


Primarily, the glossary simply defines "hierarchy" and "DAG" (Directed
Acyclic Graph), where DAG is a collection of hierarchies that are
mapped onto a flat collection of resources, where any resource can be a
member of multiple hierarchies within the DAG.


Based on this starting point and Erik's suggestion as to how the
concepts might be applied in the real world, I did further
investigation and have come to some additional preliminary conclusions
on which I think the next step to address this spec should be based.



  
The most significant conclusion I have reached is that the
primary "problem" with the non-xml resources (section 3.2) is that the
details here are solving a much more complicated problem than is
necessary for most common use cases, which is that the resources are
identified with URIs as described in section 2.2 and 4.3.


In particular, this "more complicated problem" is one where the
resource-id, itself, is not sufficient to describe the hierarchy of
which it is a member. An example might be resources identified by
serial number (a flat namespace), as opposed to resources identified by
URI, which is an inherently hierarchical namespace
(http://www.ietf.org/rfc/rfc2396.txt).


With a hierarchical namespace there is no need to collect parent and
ancestor nodes since they are already built in to the URI itself. In
fact, there is an example document that I "found", that was produced as
an artifact of the XACML 2.0 development effort, that appears to have
gotten lost from the active XACML collection:

http://www.oasis-open.org/committees/download.php/7315/xacml-profile-hierarchical-resources-nonXML-1.0-draft01.pdf


that demonstrates this quite clearly: section 4.2 shows policies based
on resource-ancestor and resource-parent attributes, and section 4.3
shows the same policies based on matching anyURI. i.e. if the resources
are identified by URI there is no need to use resource-parent and
resource-ancestor attributes either in the RequestContext or in the
Policies.


Based on this situation, my proposal is to enhance the existing
Hierarchical spec using the URI representation in section 3.2 and
indicating that this approach can be used instead of resource-parent
and ancestor when the hierarchies are represented by nodes with URI
resource-ids.


  
  
A 2nd significant problem I believe I have found is that the
algorithms defined in section 3.2 are incorrect in some significant
ways, which I believe should be addressed (I will give an example
below).


My proposal here is to simply fix the algorithms.


  
  
A 3rd significant problem I believe I have found is that there
are important concepts that are either left out or not given sufficient
emphasis in the spec, which, imo, cause conceptual ambiguities that
make it effectively impossible to say what problem the specification is
actually addressing.


In particular, there is no explicit definition of "normative identity",
which is a key term used in the algorithms defined in section 3.2.

My proposal here is to assert that the normative identity may use
either the recommended representation of URI described in section 2.2,
or a functionally equivalent representation, such as can be constructed
using resource-parent and resource-ancestor node collections.


In particular, there is insufficient development of the concept of
"consistent representations for identities" as mentioned in section 1,
lines 68-72,  section 2, lines 175-178, section 3, lines 227-229. While
the point is made that such consistent representations are necessary,
the essential fact that in a DAG that a single node can have multiple
normative identities AND that those identities each belong to a
separate distinct hierarchy within the DAG is not established. The
result is that it is conceptually ambiguous that when a node is said to
have multiple parents, the essential fact is that the node must then
have multiple normative identities, each of which is traceable to one
and only one parent (or self, if the current node happens to be the top
of one of the hierarchies within the DAG).

My proposal here is to adjust the text to emphasize these notions
accordingly.

One final note: I appreciate the significant effort that went into the
development of the Hierarchical specification. A review of the emails
from April 2004 -> September 2004 will show anyone interested that a
lot of work went into the development of this specification. My own
interpretation of the problems I have had with this spec is that it was
a relatively small, but considered to be important, part of XACML 2.0
and that while the ideas collected in this spec are generally properly
targeted, it appears there was simply not sufficient time available for
the TC to consolidate the findings of their studies of the hierarchy
problem and to structurally sort the results into separable pieces that
would have made the results easier to understand and apply.


This effort is intended to build on the existing spec and emphasize
aspects of it that currently are not, and to correct any problems that
may be found in the process.


As indicated above, I will give an example of what I consider to be an
"error" in the algorithms of section 3.2:

In section 3.2 the descriptions appear to be lterally
"over-specified": for example, consider lines 324-327:

  
" For each immediate parent of the node specified in the
“resource-id” attribute or attributes, and for each normative
representation of that parent node, an <Attribute> element with
AttributeId “urn:oasis::names:tc:xacml:2.0:resource:resource-parent”. "

  
This statement is indicating that the node "specified in the
'resource-id' attribute or attributes" can have multiple parents and
that each of those parents themselves can have multiple normative
representations.


I claim that the quoted statement is incorrect because while the given
node can have multiple parents, because the current node may belong to
multiple hierarchies, there should be no concern for hierarchies that
the parent belongs to that the current node does not belong to.


The following example will show why this is doubly and actually triply
specified and also why it is essential that the changes described in
1-3 above are needed.


Consider 3 hierarchies:

  

    
/a1/b1/c1
    
/a2/b2/c2
    
/a3/b3/c3
  
Let's say that a1, a2, and a3 are distinct roots and represent 3
separate nodes (or resources) in the overall collection.


However, let us also say that b1 is a node that belongs to all 3
hierarchies and that, in fact, /a1/b1, /a2/b2, and /a3/b3 all represent
normative identities of the same node.


Now let us further assume that c1 and c2 represent the same physical
node, but that c3 is a different node.


Let's also assume that these physical nodes have serial numbers r*,
which serve as alternate unique identifiers of the nodes. We can then
see the relation as follows:

  

    
Let r1, r2, r3 be serial numbers of the 3 separate root nodes.
    
Let r4 be the serial number of the b1,b2,b3 node.
    
Let r5 be the serial number of the c1,c2 node.
    
Let r6 be the serial number of the c3 node.

  
The logical and physical resources and hierarchies can now be
represented together as follows:

  

    
/a1(r1)/b1(r4)/c1(r5)
    
/a2(r2)/b2(r4)/c2(r5)
    
/a3(r3)/b3(r4)/c3(r6)
  
From the above, it is clear that if we are requesting access to, say
node /a1/b1/c1, then to apply the rules quoted above for parents, we
would need to first include:

  

    
/a1(r1)/b1(r4)/c1(r5)
    
/a2(r2)/b2(r4)/c2(r5)
  
where the 2 parents of c1(r5) are

  

    
/a1/b1
    
/a2/b2
  
i.e. c1, which is r5, which is then also c2, effectively has these 2
parents.


However, the rule then requires us to collect all the normative
identities of each of the parents.


First of all in this case the parent rule requires us to collect the
normative identities of r4 twice, once in its a1/b1 incarnation at
which point it also picks up a2/b2, and once in its a2/b2 incarnation,
where it picks up a1/b1 again. Therefore it is already "over-specified"
because it requires collecting these identities twice resulting in 4
instead of 2 "normative parent identities".


Furthermore, the algorithm also requires us to pick up /a3/b3, which is
another "normative identity" of this parent node, which means we will
have 3 copies of each normative identity of the "parents" of c1 for a
total of 9 "normative parent identities", which are, of course triply
redundant.


In fact, we really only need /a1/b1 and /a2/b2 since r5 does not belong
to the /a3/b3 hierarchy.


Therefore this algorithm needs at least 2 corrections:

  

    
Correct it so that it only includes one copy of each normative
identity of each parent.
    
Correct it so that it does not include normative identities of
the parent which are part of hierarchies to which it does not belong,
since policies on those hierarchies can have no bearing on this node
because the normative representations within those hierarchies cannot
refer to this node because it does not have a normative representation
in those hierarchies to which it does not belong.
  

Comments and suggestions are welcome. I will wait for feedback on
emails and discussion at the next TC meeting before proceeding with the
recommended changes.


    Thanks,

    Rich









Rich.Levinson wrote:
496F6636.9010801@oracle.com" type="cite">

                                                

					
                                                    

        
                                                
				
                                                

                                                    
                                                        
                                                        Original Message
                                                
                                                
Original Message --------
  

    

      

        
Subject: 
        
Re: [xacml] Issue: Hierarchical profile appears ambiguous
and inconsistent
      
      

        
Date: 
        
Thu, 15 Jan 2009 11:37:10 -0500
      
      

        
From: 
        
Rich.Levinson <rich.levinson@oracle.com>
      
      

        
To: 
        
Erik Rissanen <erik@axiomatics.com>
      
      

        
CC: 
        
Daniel Engovatov <daniel@streamdynamics.com>, xacml
<xacml@lists.oasis-open.org>
      
      

        
References:
        
        
<496EDDA0.4070707@oracle.com>
<1448A6CC-1532-40B4-BFC0-DC9D0413097E@streamdynamics.com>
<496F4B67.1040700@oracle.com>
<496F4DC8.4030200@axiomatics.com>
      
    
  



Hi Erik,


Thanks for this feedback. Unfortunately I did not have time to process
this email before today's meeting, but now that I have, it addresses
one of my major concerns which was the motivational context. i.e. by
seeing the actual example you provided, I can see that a Policy can now
base decisions knowing that some node happens to be an ancestor of the
requested node.


In addition, for your example, I think it would be instructive to show
when a node belongs to two or more hierarchies, that the collection of
attributes should probably have a mechanism to indicate which hierarchy
a node belongs to. For example, if C had an alias C', and parent B' and
ancestors A'->D' where, while (C = C'), that in general (B != B')
and (A != A') and obviously D' has no relation to the unprimed nodes at
all. We would then have a request:


   <Resource>

    resource-id = C

    parent-id = B

    self-or-ancestor = C

    self-or-ancestor = B

    self-or-ancestor = A

    resource-id = C'

    parent-id = B'

    self-or-ancestor = C'

    self-or-ancestor = B'

    self-or-ancestor = A'

    self-or-ancestor = D'

   </Resource>


It would seem to me that there needs to be a mechanism whereby one
would be able to tell the primed from unprimed attributes. Possibly
using Issuer


In any event, it is useful information to have this additional context
for understanding the current spec.


As agreed at the meeting, I will try to find some cycles to say what I
think needs to be done to make the spec easier to understand, which is
possibly just including the above information (i.e. your email extended
to multiple hierarchies with some example policy concepts, also such as
you provided).


Also, I think, as I mentioned at the end of the meeting that "scope"
may also have a meaningful role to include in this profile as well.
i.e. one can easily see that if policies are defined whereby certain
conditions apply when a resource-id node is within scope (as defined by
multi-resource spec) of some other node, that some if that ""other
node" happens to be a parent or ancestor of the resource-id node, then
those "certain conditions" would apply to the current resource-id being
requested.


   Thanks,

   Rich





Erik Rissanen wrote:

  
Rich.Levinson wrote:
I am trying to understand what policies are
supposed to do with the definitions in the spec. i.e. it is the spec
that says in section 3.2 that all the parent and ancestor nodes need to
be assembled in the request context. What "policy evaluation" are you
referring to? Are you saying what I indicated in original email that a
policy does not need to know anything about hierarchies that the
resource-id node does not belong to?


Hi Rich,


I don't understand all the questions you have, but here's the basic
approach of the profile in a simple example.


Assume the following simple hierarchy:


A <- B <- C


If someone requests access to C, the request will contain these
attributes. this is from the top of my head, so it might be slightly
inaccurate and I might have forgotten some of the attributes, but
hopefully you get the idea.


<Resource>

 resource-id = C

 parent-id = B

 self-or-ancestor = C

 self-or-ancestor = B

 self-or-ancestor = A

</Resource>


All these attributes are there so it is possible to write policies
which apply to parts of the hierarchy, not just individual nodes.


For example:


<Target>

 resource-id = C

</Target>


Matches only the resource C, nothing else.



<Target>

 parent-id = B

</Target>


matches the immediate children of B. In the example this is C, but if C
had a sibling, it would also match.




<Target>

 ancestor-or-self = B

</Target>


Matches B or any node below B. In this case also C.


Best regards,

Erik


  
  


Original Message --------
  

    

      

        
Subject: 
        
[xacml] Issue: Hierarchical profile appears ambiguous and
inconsistent
      
      

        
Date: 
        
Thu, 15 Jan 2009 01:54:24 -0500
      
      

        
From: 
        
Rich.Levinson <rich.levinson@oracle.com>
      
      

        
To: 
        
xacml <xacml@lists.oasis-open.org>
      
    
  



I am finding the Hierarchical profile ambiguous and inconsistent and
therefore incomprehensible, which may, similarly to the Multi-Resource
profile be because there are essential contextual paradigms missing
from the specification.


For the Multi-Resource profile, the missing contextual paradigms
included:


   * It is necessary to pre-process the multi-resource request and

     submit individual requests to the PDP, and then to package up the

     responses into a single response.

   * The PDP, itself, can only process Request elements that in 2.0

     contain a single Resource element, single Action element, single

     Environment element, and multiple Subject elements, but each

     Subject element has to have a distinct SubjectCategory attribute,

     and in 3.0 there can be multiple Attributes elements, but each has

     to have a distinct Category attribute.


Once the above paradigms are established, the Multi-Resource profiles
become comprehensible.


I suspect something similar is going on w the Hierarchical profile
also.


Here is the background on the Hierarchical profile that I am trying to
work thru (each bullet represents a potential issue to resolve or
suggestion for improvement):


   * There needs to be a definition of "hierarchy". In particular, a

     "hierarchy" defn should state that the fundamental properties are

     that there must be a single root node with no parent, and that

     every other node in the hierarchy must have one and only one

     parent, and can have zero, one, or more children.

   * Section 3.2 is the biggest problem. To begin, the following needs

     confirmation: it appears that the key structural sentence for 3.2

     that explains what the four bullets that follow it are is lines

     314-315 (which is sandwiched between a negative statement on

     ResourceContent and subsequent 3 sentence "note") that state:

         o "The request context <Resource> element SHALL contain
the

           following elements and XML attributes."

   * Each of the 4 bullets in section 3.2 contains the phrase "(for

     each) normative representation (of some node ...)". I think this

     is the core of the problem I am having understanding this spec.

     What I think it means is that for a given collection of physical

     resources, such as files in a file system, that in additional to

     the conventional file identification by directory path, which

     includes all the files in the file system, that other logical

     hierarchies that can span part or all of this set of resources

     also needs to be taken into account. And that the "normative

     identity" of a specific "file" is within the context of a specific

     hierarchy. i.e. each hierarchy that covers all or part of this set

     of resources has its own "namespace" and within that namespace has

     a scheme for hierarchically naming its members. As such, a given

     physical resource can belong to any number of these hierarchies

     simultaneously, and has one "normative representation" for each

     hierarchy it belongs to. And presumably, the point is that each

     hierarchy the resource belongs to may have its own restrictions to

     apply to resource, so we have to identify all of them to get the

     full picture.

   * Given the above characterization of the multiple "hierarchies" a

     given resource can belong to, it then appears that the four

     bullets in section 3.2 state that in order to submit a request,

     one has to somehow identify all the hierarchies the given node

     belongs to, all the hierarchies the node's parent(s) and ancestors

     to, and include an Attribute element for each.

   * There appears to be some over-specification above and beyond what

     is presumably intended (assuming the above characterizes what is

     "presumably intended"). For example, since a node in a hierarchy

     can have only one parent, and if a node belongs to multiple

     hierarchies, then that node will have one and only one parent for

     each hierarchy it belongs to, the following sentence (lines

     324-325) appears to doubly state this relationship:

         o "For each immediate parent of the node specified in the

           “resource-id” attribute or attributes, and for each

           normative representation of that parent node ..."

           i.e. the node specified in the resource-id can only have one

           parent wrt the the node's normative representation with a

           specific hierarchy. There seems to be no point to looking at

           a parent node in any other context than the normative

           context of the resource-id node. i.e. if a node only belongs

           to one hierarchy, but its parent belongs to many, then the

           other hierarchies the parent belongs to should have no

           impact on the child since the child is not a member of those

           hierarchies.


Assuming the above characterization is even close to correct, I am
still wondering "why" all this information is being assembled and what
the Policy is expected to do with it. i.e. what is the policy
evaluation paradigm that is being represented here? I suspect that at
most one would need to collect all the normative representations of
only the resource-id node (i.e. identify all the hierarchies it belongs
to), then for each hierarchy, one would evaluate the policies that
apply to that hierarchy.


Thanks,

Rich



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Based on this situation, my proposal is to enhance the existing Hierarchical spec using the URI representation in section 3.2 and indicating that this approach can be used instead of resource-parent and ancestor when the hierarchies are represented by nodes with URI resource-ids.

Using URI is a very limited approach, and it can be trivially mapped into "ancestor" approach.    Requiring a unique URI for resources is often not feasible

 The following example will show why this is doubly and actually triply specified and also why it is essential that the changes described in 1-3 above are needed.

 Consider 3 hierarchies:
  
    
/a1/b1/c1
    
/a2/b2/c2
    
/a3/b3/c3
  
 Let's say that a1, a2, and a3 are distinct roots and represent 3 separate nodes (or resources) in the overall collection.

I think you are confusing physical resources and policy resources.    Such mapping is outside of XACML.    There is no real hierarchy in XACML, we just provide a convenient normative way to represent them - only for the purpose of using it in a policy target.

For the purpose of a single policy evaluation hierarchy that is used is uniquely defined by the provided "resource-ancestors" attribute.   The fact that there is some persistent identity that may participate in different hierarchies should be outside of the scope of this profile.

Daniel;

  


Hi Daniel,


See replies inline:


Daniel Engovatov wrote:
daniel@streamdynamics.com,0E0925E7-45E3-468F-B4FF-08BC9" type="cite">
  
Based on this situation, my proposal is to
enhance the existing Hierarchical spec using the URI representation in
section 3.2 and indicating that this approach can be used instead of
resource-parent and ancestor when the hierarchies are represented by
nodes with URI resource-ids.

  


Using URI is a very limited approach, and it can be trivially mapped
into "ancestor" approach.    Requiring a unique URI for resources is
often not feasible


I am not recommending removing or replacing what is there, but simply
representing the URI approach and the manner in which it can be used in
parallel. When the URI is present, there is no need to create the
ancestors, and one may simply use the anyURI-regexp-match as specified
in section 4.3 (which I notice now needs to be updated to be consistent
w core). Also, as stands, 4.3 really should have corresponding
description in 3.2, which it currently does not.

I am not recommending requiring URI, but only making it available when
convenient, which I think includes quite a broad range of use cases and
I would not characterize it as "very limited" despite the fact that it
may not be "universally applied".

My objectives are usability of the policy language. Scoping based on
URI  regular expression matching is a universal technique, which is
much easier than parsing URIs into parents and ancestors and then using
XPath-type referencing, which is the approach indicated by Erik's
example.

As you and others have indicated in the 2004 emails, there are use
cases where URI is not readily available or desired, and the mechanisms
from XPath are very useful there and I have no intention to remove
them, but only to "correct" them, if need be, as indicated by the
example I included in prev email.

daniel@streamdynamics.com,0E0925E7-45E3-468F-B4FF-08BC9" type="cite">

  
The following example will show why this is
doubly and actually triply specified and also why it is essential that
the changes described in 1-3 above are needed.


Consider 3 hierarchies:

/a1/b1/c1

/a2/b2/c2

/a3/b3/c3

Let's say that a1, a2, and a3 are distinct roots and represent 3
separate nodes (or resources) in the overall collection.

  


I think you are confusing physical resources and policy resources.   
Such mapping is outside of XACML.    There is no real hierarchy in
XACML, we just provide a convenient normative way to represent them -
only for the purpose of using it in a policy target.


I do not believe I am confusing the two. Physical resources are a fact
of existence and in the case of XACML, the hierarchical identifiers are
simply labels that the managers of those resources have applied to
them. In the example I gave, it is the r* that represent the physical
labels on the physical resources. They are an unordered flat
collection. All the /a*/b*/c* are hierarchical representations of
subsets of those resources. A given instance of "*" represents one
hierarchy that is mapped onto the physical resources. All the policies
deal with are the hierarchical representations. The physical is only
mentioned to give people some context for understanding what is being
discussed.

For example, all the PCs in a company have serial numbers.
When managers create policies, they have the physical resources in mind
and may organize them hierarchically for various purposes. A department
manager may label the PCs in his/her dept according to some
hierarchical structure in the dept organization and assign policies
accordingly. At the same time these PCs are company property and may be
labeled independently by the IT dept in terms of who is responsible for
maintenance on them.


If someone wants to take one of these PCs out of the building, maybe
there is a policy that says even if the employee's manager says it is
ok, the facilities manager must also approve before permission is
granted. This can be modeled with a dept hierarchy and a facilities
hierarchy, and there are rules within the hierarchy producing a result
and policy combining between the 2 hierarchies that can resolve
conflicts such as described above.


In the above example the /a1/b1/c1 might be the dept hierarchy and
/a2/b2/c2 might be the facilities hierarchy.


daniel@streamdynamics.com,0E0925E7-45E3-468F-B4FF-08BC9" type="cite">

For the purpose of a single policy evaluation hierarchy that is used is
uniquely defined by the provided "resource-ancestors" attribute.   
It is also uniquely defined by a URI if a URI scheme has been applied
to the same resources, since all the ancestors are readily identifiable
within the URI.

daniel@streamdynamics.com,0E0925E7-45E3-468F-B4FF-08BC9" type="cite">The fact that there is some persistent identity that may
participate in different hierarchies should be outside of the scope of
this profile.


As indicated above and original email, the r* persistent identity is
only used as contextual reference for humans to know what is being
discussed. Within the policies themselves, there would generally be no
need to include this attribute except possibly for reporting purposes.


    Thanks,

    Rich

daniel@streamdynamics.com,0E0925E7-45E3-468F-B4FF-08BC9" type="cite">

Daniel;

> For example, all the PCs in a company have serial numbers. When  
> managers create policies, they have the physical resources in mind  
> and may organize them hierarchically for various purposes. A  
> department manager may label the PCs in his/her dept according to  
> some hierarchical structure in the dept organization and assign  
> policies accordingly. At the same time these PCs are company  
> property and may be labeled independently by the IT dept in terms  
> of who is responsible for maintenance on them.
>
> If someone wants to take one of these PCs out of the building,  
> maybe there is a policy that says even if the employee's manager  
> says it is ok, the facilities manager must also approve before  
> permission is granted. This can be modeled with a dept hierarchy  
> and a facilities hierarchy, and there are rules within the  
> hierarchy producing a result and policy combining between the 2  
> hierarchies that can resolve conflicts such as described above.
>
> In the above example the /a1/b1/c1 might be the dept hierarchy and / 
> a2/b2/c2 might be the facilities hierarchy.

There is no need for separate hierarchies here if the "remove from  
building" is a single access decision.  In your example, let's "PC"  
be a resource, "DEPT" be a department, and "FACILITIES" be  
facilities.     In this case resource-ancestors will be {"PC",  
"DEPT", "FACILITIES"}    (or {"a1", "a2", "b1", "b2", "c"} )  There  
is no need for two hierarchies.   That is the advantage of not being  
pidgeonholed into a single inheritance URI-like scheme.

> It is also uniquely defined by a URI if a URI scheme has been  
> applied to the same resources, since all the ancestors are readily  
> identifiable within the URI.

That's a bit of a contorted way to represent a simple bag of strings.

>  Within the policies themselves, there would generally be no need  
> to include this attribute except possibly for reporting purposes.

Then what exactly is the problem?   Policy, as specified, can be  
evaluated deterministically.   The mapping of physical entities into  
policy resources is outside of the scope of this profile.   I do not  
see anything broken here.

Daniel;

  


Hi Daniel,


I am not sure exactly what you are driving at here, but I include
comments below:


Daniel Engovatov wrote:
daniel@streamdynamics.com,4BD684A8-1AF9-4E23-AB83-0EB76" type="cite">
  
For example, all the PCs in a company have
serial numbers. When managers create policies, they have the physical
resources in mind and may organize them hierarchically for various
purposes. A department manager may label the PCs in his/her dept
according to some hierarchical structure in the dept organization and
assign policies accordingly. At the same time these PCs are company
property and may be labeled independently by the IT dept in terms of
who is responsible for maintenance on them.


If someone wants to take one of these PCs out of the building, maybe
there is a policy that says even if the employee's manager says it is
ok, the facilities manager must also approve before permission is
granted. This can be modeled with a dept hierarchy and a facilities
hierarchy, and there are rules within the hierarchy producing a result
and policy combining between the 2 hierarchies that can resolve
conflicts such as described above.


In the above example the /a1/b1/c1 might be the dept hierarchy and
/a2/b2/c2 might be the facilities hierarchy.

  


There is no need for separate hierarchies here if the "remove from
building" is a single access decision.  In your example, let's "PC" be
a resource, "DEPT" be a department, and "FACILITIES" be facilities.    
In this case resource-ancestors will be {"PC", "DEPT", "FACILITIES"}   
(or {"a1", "a2", "b1", "b2", "c"} )  There is no need for two
hierarchies.   That is the advantage of not being pidgeonholed into a
single inheritance URI-like scheme.


The hypothetical scenario I am describing is based on two
sub-organizations within a larger organization which operate
independently on the same set of physical resources. In general, the
operations are independent, but in some cases there is need for both
organizations to be brought into some kinds of decision. The dept
manager has set up a hierarchy for controlling the PCs in his
department, while the facilities manager has set up an independent
hierarchy on the same set of PCs for controlling the maintenance on
those PCs from within the facilities organization.


The parent organization recognizes that there may be situations where
the decisions of the two organizations may come into conflict and have
set up combining algorithms above the two hierarchies to resolve
differences.


From what you are saying, and I do not follow your example, it sounds
like it is possible to restructure the existing hierarchies into a new
framework where somehow the existing hierarchies no longer need to
exist. This may be useful as an academic exercise, but operationally,
one would need to educate the company, the facilities and the
department about this new uniform paradigm and explain to the people
involved why they no longer need the hierarchical representations.


However, I do not understand precisely what you are recommending:


  
I do not understand how {"PC", "DEPT", "FACILITIES"} relates to
the scenario I have described. I have specific PCs, in the example they
have serial numbers r5, r6. One of these PCs, r5, is identified in the
"dept" as /a1/b1/c1. In the facilities org the same pc is identified as
/a2/b2/c2.

  
  
The ancestor nodes of /a1/b1/c1 and /a2/b2/c2 are the same,
namely {/a1, /a1/b1, /a2, /a2/b2}. I do not see how you can say {"a1",
"a2", "b1", "b2", "c"}. "c" is not one of the terms. "a2" and "b2" by
themselves are not normative identities. 

daniel@streamdynamics.com,4BD684A8-1AF9-4E23-AB83-0EB76" type="cite">

  
It is also uniquely defined by a URI if a URI
scheme has been applied to the same resources, since all the ancestors
are readily identifiable within the URI.

  


That's a bit of a contorted way to represent a simple bag of strings.


URIs do not represent bags of strings. Possibly one might choose to
represent a URI as a bag of strings, however, one loses the ordering in
the process. If one wants to identify the specific set of nodes
represented by a URI, it is a simple matter to sequentially strip one
component at a time off the URI, and at each step one has the normative
identity of the next node up the chain until one reaches the root.

daniel@streamdynamics.com,4BD684A8-1AF9-4E23-AB83-0EB76" type="cite">

  
 Within the policies themselves, there would
generally be no need to include this attribute except possibly for
reporting purposes.

  


Then what exactly is the problem?   Policy, as specified, can be
evaluated deterministically.   The mapping of physical entities into
policy resources is outside of the scope of this profile.   I do not
see anything broken here.
I was addressing the statement you made that you thought I had a
problem confusing the physical and policy resources. I was showing that
the physical mapping was simply an orthogonal property of the node
which of necessity must include an identity for each of its purposes,
in this case: one for the dept, one for the facilities, and one for the
physical identifier. However, for policies, the physical identifier
need not be used and may be regarded as a resource attribute on the
node entity outside of the policy structures, but available to be
included if necessary.


At this point I fail to understand the purpose of specifically not
using a hierarchical naming scheme in order to identify a set of
resources that will be managed as a hierarchy. I understand that there
may be cases where for some reason it may not be possible or practical
to use such a naming scheme, but in those cases where it is possible
and practical, I do not understand why it would not be a good idea to
use it.


    Thanks,

    Rich


daniel@streamdynamics.com,4BD684A8-1AF9-4E23-AB83-0EB76" type="cite">


Daniel;