Hi Rich,
I don't think I understand what you mean.
The commenter's resources are not disjoint. They are a DAG. Therefore he
wants to use the "ancestor scheme" without URIs.
Regards,
Erik
Rich.Levinson wrote:
> Hi Erik,
>
> The commenter states the problem he is trying to solve as:
>
> * "I have a rule that says "permit if resource has ancestor 'path'"."
>
> It is only after he follows the erroneous directions in section 3.2
> that he runs into trouble, whereas if he used the suggestion in my
> previous email the problem would already be solved and we would have
> no issue.
>
> I have done further research into this and I think that I can now say
> unambiguously that section the bulleted algorithms in section 3.2 are
> simply wrong, because they are based on an erroneous premise.
>
> The erroneous premise is that it is assumed that a forest is the same
> as a DAG. In fact, they are not the same. In particular, a forest is
> generally defined as a *disjoint set of trees*. The important word in
> this phrase is "disjoint". There are many reasons why this problem
> must be modeled as a disjoint set, several of which have been covered
> in previous emails.
>
> The algorithms in section 3.2 are specifically not disjoint, which is
> why they are in error. This error is simply corrected by a minor
> modification to ensure disjointness.
>
> At this point I would like to raise this to a formal issue, which I
> would categorize as a recommendation to correct a SEVERE ERROR in the
> Hierarchical Profile Specification.
>
> We have already seen evidence as reported by this commenter that the
> errors in this specification are leading users to do wrong and
> irrelevant work, and we now have specific formal definitions of the
> terms that express exactly what the error is and how it can be corrected.
>
> Thanks,
> Rich
>
>
>
>
> Erik Rissanen wrote:
>> Hi Rich,
>>
>> My understanding is that the commenter does not want to use URIs at
>> all. Instead he wants to do it like this:
>>
>> resource-id=r1
>> resource-ancestor=path
>> resource-ancestor=to
>> resource-ancestor=one
>> resource-ancestor=another
>>
>> URI matching wouldn't help him.
>>
>> Regards,
>> Erik
>>
>>
>> Rich.Levinson wrote:
>>> Hi Erik,
>>>
>>> With regard to your 2nd point on the comments/users list, it appears
>>> to me that because the Hierarchical spec has the problems that I
>>> have described in earlier emails, that the user has posed his
>>> question in such a way that instead of advising the commenter on
>>> what appears to me to be a simple obvious way to solve his problem,
>>> you instead have been drawn into considering the user's suggestion
>>> that we change the specs from the current explicit description in
>>> section 2.2 to one that appears to me would significantly undermine
>>> the intent of the current section 2.2.
>>>
>>> Now that we have hammered away at the hierarchical profile for
>>> several emails, and if people have been reading the details, we can
>>> now take another look at the question the commenter raised, which I
>>> had previously said we should revisit in the context of my proposal
>>> (item 3 here:
>>> http://lists.oasis-open.org/archives/xacml/200902/msg00004.html).
>>>
>>> The commenter's question is here:
>>> http://lists.oasis-open.org/archives/xacml-comment/200901/msg00003.html
>>>
>>> Your reply to him, where you said you would bring the issue to the
>>> TC, is here:
>>> http://lists.oasis-open.org/archives/xacml/200901/msg00056.html
>>>
>>> This example shows exactly why I believe it is NECESSARY to add the
>>> clarifying text that I have been talking about to section 3.2.
>>>
>>> It appears to me that this user has been clearly misled by the spec
>>> to attempt to do what seems to me to be a wasteful and pointless
>>> exercise of parsing URIs and then trying to make sense of the
>>> collection of artifacts that he has produced. It appears to me that
>>> this is totally unnecessary, and I would suggest that it has been a
>>> waste of his time for being led down this path by the
>>> specifications, which is the point I have repeatedly been making
>>> that the specs are insufficient in section 3.2 in this regard .
>>>
>>> I am concerned that instead of addressing this type of problem with
>>> the capabilities currently in the spec, that we are being drawn down
>>> a path, which will effectively dismantle the perfectly good
>>> functionality that is in the spec by removing the URI capability as
>>> it currently exists.
>>>
>>> I think this user should be told that since his nodes are currently
>>> identified by URIs that are in the form called for in section 2.2
>>> that he does not need to worry about collecting ancestors etc. and
>>> all he needs to do is apply the XACML 2.0 anyURI-regexp-match as
>>> described in section A.3.13 of the core spec and his problem is solved.
>>>
>>> As described in section 4.3 of the example doc in the archive
>>> (http://www.oasis-open.org/committees/download.php/7315/xacml-profile-hierarchical-resources-nonXML-1.0-draft01.pdf),
>>> this function is simply specified as:
>>> <Apply FunctionId="&anyURI-regexp-match;">
>>> <AttributeValue DataType="&string;"
>>> >http://example.com/path/*</AttributeValue>
>>> <Apply FunctionId="&string-one-and-only;">
>>> <ResourceAttributeDesignator AttributeId="&resource-id;"
>>> DataType="&string;">
>>> </Apply>
>>> </Apply>
>>>
>>> This is the kind of guidance I am recommending that we add to
>>> section 3.2 of the Hierarchical Profile.
>>>
>>> As I understand your email, an alternative suggestion to address
>>> this user situation is to recommend that the user parse his URIs
>>> into components, and that we change the spec to alter the currently
>>> defined URI capability (to no longer be a URI capability, with all
>>> the inherent capabilities of a URI) in order that the customer be
>>> able to do this?
>>>
>>> Let me further point out that I don't think there is any need to
>>> change the spec, because it already says in section 2 that governs
>>> 2.2 that:
>>>
>>> "The following sections describe RECOMMENDED representations for
>>> nodes in hierarchical resources. Alternative representations of
>>> nodes in a given resource are permitted so long as all Policy
>>> Administration Points and all Policy Enforcement Points that deal
>>> with that resource have contracted to use the alternative
>>> representation."
>>>
>>> Therefore, if for some reason we advise against using what appears
>>> to me to be an obvious standard capability described above with
>>> anyURI-regexp-match, and would like users instead to parse their
>>> URIs into components so that they can supply the components as a
>>> collection of ancestors, I believe we are still able to do this
>>> because the statement above appears to explicitly allows for nonURI
>>> representations, in which case we would not have to do anything to
>>> section 2.2.
>>>
>>> However, to be perfectly honest, I still see no advantage to
>>> applying the bulleted capability procedure of section 3.2 to nodes
>>> that are already identified by URIs.
>>>
>>> Comments welcome. I would really like to understand if there is a
>>> legitimate reason for not using the URIs as is and replacing them by
>>> collections of components.
>>>
>>> Thanks, Rich
>>>
>>>
>>>
>>>
>>>
>>> Erik Rissanen wrote:
>>>> All,
>>>>
>>>> I've been in a rush today, so I haven't followed every detail in
>>>> the discussion, but basically, here is how it appears to me:
>>>>
>>>> * The profile, as it stands today, does specify the limited URI
>>>> scheme which Rich describes. It says in section 2.2 that:
>>>>
>>>> --8<--
>>>> The <pathname> portion of the URI SHALL be of the form
>>>>
>>>> <root name> [ “/” <node name> ]*
>>>>
>>>> The sequence of <root name> and <node name> values SHALL correspond
>>>> to the individual hierarchical component names of ancestors of the
>>>> represented node along the path from a <root> node to the
>>>> represented node.
>>>> --8<--
>>>>
>>>> So it in fact says that the identifiers must consists of paths with
>>>> the names of the ancestors.
>>>>
>>>> * If I understand Daniel correctly, he says that each node should
>>>> be allowed to have a name which is entirely independent of the
>>>> other nodes in the hierarchy. Relations between the nodes are
>>>> maintained in a manner not specified by XACML and are expressed in
>>>> XACML Requests and policies in the form of the attributes
>>>> resource-parent, resource-ancestor, etc. I think that the more
>>>> general approach advocated by Daniel would be the correct way to
>>>> go, so I agree with him (and Seth I believe. :-))
>>>>
>>>> * I also think as suggested on the XACML comments/users list that
>>>> the data type of the node identifier should not be limited to URIs
>>>> only.
>>>>
>>>> But I would prefer to leave major changes to the hierarchical
>>>> profile out of the first batch of CD documents.
>>>>
>>>> Best regards,
>>>> Erik
>>>>
>>>>
>>>> Rich.Levinson wrote:
>>>>> Hi Daniel and TC,
>>>>>
>>>>> Hopefully, those who have followed the details of these emails
>>>>> recognize that each step in the sequence has advanced the
>>>>> discussion in a consistent manner and as a result we have done a
>>>>> fairly thorough job of mapping out the problem space that is under
>>>>> discussion. In any event I believe my comments in this email
>>>>> continue to advance the discussion in a worthwhile manner, and I
>>>>> think will describe the complete problem space as well as give a
>>>>> clear description of the options available, all of which offer
>>>>> full functionality.
>>>>>
>>>>> In the current phase, if I am not mistaken, it is a
>>>>> straight-forward matter to apply definitions to the distinct
>>>>> categories of problems and simply observe that we have two sets of
>>>>> tools which are equally effective at solving each category of
>>>>> problem, where
>>>>>
>>>>> * one set of tools (let's call it the "ancestor method") is most
>>>>> effective when one is dealing with resources where it is not
>>>>> possible or desirable to apply URIs as normative identifiers
>>>>> * a second set of tools (let's call it the "URI method") which is
>>>>> available when one is dealing with resources where URIs can be
>>>>> applied as normative identifiers, and the designers want to
>>>>> take
>>>>> advantage of the powerful features inherent in URI objects, esp
>>>>> when applied to hierarchical problems.
>>>>>
>>>>> Let me address Daniel's points below, then try to summarize the
>>>>> present state of the discussion:
>>>>>
>>>>> Daniel Engovatov wrote:
>>>>>>
>>>>>> On Feb 18, 2009, at 3:05 PM, Rich.Levinson wrote:
>>>>>>
>>>>>>> Daniel, Seth, Erik, and TC,
>>>>>>>
>>>>>>> If we stick to the generally accepted definition that an object
>>>>>>> in a hierarchy can have at most one parent, then a URI solves
>>>>>>> the problem without having to look beyond the URI itself
>>>>>>
>>>>>> It is NOT a generally accepted definition and we did not stick to
>>>>>> it on purpose.
>>>>>>
>>>>> Whether it is generally accepted or not is probably not important
>>>>> here, however, it is consistent with the structure of XML
>>>>> documents, such that when we are talking about a "single
>>>>> hierarchy" of nonXML resources that if we assert that this implies
>>>>> a structural relationship equivalent to the structural
>>>>> relationship of the nodes of a well-formed XML document, which is
>>>>> that each element can have at most one parent, and the top element
>>>>> or node has zero parents.
>>>>>
>>>>> This gives us a crisp unambiguous definition of the term
>>>>> "hierarchy" which can be applied both to the XML and nonXML
>>>>> resources, and it totally avoids trying to determine whether it is
>>>>> an "accepted" definition or not, since that property is no longer
>>>>> relevant.
>>>>>
>>>>> The point of this definition is to give us a conceptual framework
>>>>> within which to evaluate the two primary use cases of the DAG,
>>>>> which as will be explained are also clear and unambiguous
>>>>> well-defined use cases.
>>>>>>
>>>>>>> However, if we allow the hierarchies to break down and lose
>>>>>>> their inherent hierarchical properties, then more complicated
>>>>>>> approaches, such as going outside the initial request context to
>>>>>>> get more nodes, although still solvable w URIs as demo'd below,
>>>>>>> are needed.
>>>>>>>
>>>>>>
>>>>>> It is NOT "broken down"
>>>>> True, in an absolute sense nothing is "broken", however, what has
>>>>> happened is that we have allowed one class of DAG representation
>>>>> to be impacted in such a way that we have allowed it to become the
>>>>> second class of DAG representation because we did not clearly
>>>>> define the distinction and what was to be allowed and not allowed.
>>>>> This has nothing to with whether the ancestor or URI method is
>>>>> used. It has only to do with the relationships that are allowed to
>>>>> be represented when two resources are "connected" by virtue of
>>>>> their hierarchical relationship being established.
>>>>>
>>>>> Specifically, one has a choice of:
>>>>>
>>>>> 1. only allowing the relationship that is being established to be
>>>>> active. For example if my boss is assigned to be subordinate to
>>>>> a task force leader when a cross functional team is being set
>>>>> up, this case would say that has no impact on my relationship
>>>>> with the task force leader unless I am a member of the task
>>>>> force. i.e. the task force leader has control over my boss's
>>>>> resources to whatever degree is implied by the task force
>>>>> situation, however the task force leader has zero direct
>>>>> control
>>>>> over my resources as a result of this assignment. In this
>>>>> model,
>>>>> that direct control could be simply be established by either
>>>>> assigning me directly to the task force leader, or assigning me
>>>>> a second subordinate relationship to my boss in the context of
>>>>> the task force relationship.
>>>>> This is a clearly defined process, where there is no ambiguity
>>>>> about relationships between the resources. If you want the
>>>>> relationship, you explicitly establish it, if not, you don't.
>>>>>
>>>>> 2. the other choice is the exact opposite, namely allowing
>>>>> incidental relationships to be established simply because they
>>>>> connect to a node with direct relationships. To take an extreme
>>>>> light-spirited example, for the purpose of showing how
>>>>> "extraneous" relations are introduced, if the company CEO was a
>>>>> member of a company bowling team, where the captain of the
>>>>> bowling team happened to be a junior software engineer who just
>>>>> joined the company, then everyone in the company would suddenly
>>>>> have this junior engineer as their ancestor. Possibly this
>>>>> would
>>>>> be disallowed by acyclic graph rules, but a similar situation
>>>>> would occur if the VP of engineering was on a bowling team
>>>>> captained by the junior sales trainee, who would now be
>>>>> ancestor
>>>>> to everyone in engineering organization.
>>>>>
>>>>> Both methods are acceptable for assigning relationships, but one
>>>>> or the other may be more effective for one or another type of
>>>>> organization. Personally, I think most enterprise security
>>>>> departments would favor the first approach, because it appears to
>>>>> offer more direct control and less chance of unintended
>>>>> consequences resulting from the assignment of a direct relationship.
>>>>>
>>>>> However, either choice can be used with either the "ancestor
>>>>> method" or the "URI method". Which choice is made is a function of
>>>>> the node collecting algorithm that is used for policy evaluation.
>>>>> i.e. when you collect the parent nodes of the requested node,
>>>>>
>>>>> * choice 1 above means only collect those nodes to which the
>>>>> parent has a direct relationship with the requested node,
>>>>> * and choice 2 means collect all the nodes of choice 1 plus all
>>>>> other nodes where the parent has a hierarchical relationship
>>>>> that does not directly involve the requested node.
>>>>>
>>>>> These are the two primary use cases of the DAG, which were
>>>>> mentioned above. Which use case is chosen depends only on the node
>>>>> collection algorithm and not how the nodes are represented. i.e.
>>>>> parents and ancestors exist whether or not they are incorporated
>>>>> for handy access within a URI or not.
>>>>> When the URI can be used, the URI collection within the requested
>>>>> node itself contains all the nodes that will be collected with
>>>>> method 1 and there is no need to access any additional information.
>>>>>
>>>>>>
>>>>>>
>>>>>>> Again, I am not trying to add or change any of the existing
>>>>>>> functionality,
>>>>>>
>>>>>> You are proposing an addition that is a subset of the more
>>>>>> general approach.
>>>>> Hopefully, the description above satisfactorily demonstrates that
>>>>> the URIs are simply a concrete mechanism to implement the general
>>>>> solution. It is also a mechanism that, if used effectively,
>>>>> appears to be much more efficient since all nodes that need to be
>>>>> collected in method 1 actually are already contained in the URI
>>>>> collection of the requested node.
>>>>> Therefore it is a concrete representation of the general approach,
>>>>> however it is a concrete representation that capitalizes on the
>>>>> fact that the object used to represent the node (the URI) has an
>>>>> equivalent structure to the spatial relationships of the nodes in
>>>>> the DAG that need to be collected in method 1, and so those nodes
>>>>> do not need to collected at all since they are already present.
>>>>> The same structural relationship exists in method 2, however,
>>>>> method 2 fans out so far so fast that collection outside the
>>>>> requested node will be required to fulfill the needs of method 2.
>>>>> It is functionally equivalent to the general approach, however, it
>>>>> has the advantage that a single URI contains the normative
>>>>> identity of all the required nodes for method 1 and some for
>>>>> method 2.
>>>>>>
>>>>>> I understand that you favor a different approach to this problem.
>>>>>> It may be worth our while to create a separate profile for such
>>>>>> an approach, but I do not see any reason to muddy the existing one.
>>>>>>
>>>>> It should be clear from the above discussion that showing how URIs
>>>>> address the same problem is not a "different approach". It is the
>>>>> same approach, except the work required to collect the nodes is a
>>>>> lot less, and can be eliminated almost completely depending on
>>>>> what node collection strategy is chosen, method 1 or method 2.
>>>>>
>>>>> Finally, it should be clear that the bulleted algorithms in
>>>>> section 3.2 of the spec represent a nonURI approach using a method
>>>>> 2 collection algorithm.
>>>>>
>>>>> Now that the problem is clearly defined, I expect it will take
>>>>> much fewer words than have been exchanged in these emails to
>>>>> explain the available options in section 3.2, which are:
>>>>>
>>>>> 1. method 1 node collection, URI method (all nodes required are in
>>>>> requested node)
>>>>> 2. method 1 node collection, ancestor method: (requested node has
>>>>> pointers to parents, but need to recursively navigate to parent
>>>>> to advance up the hierarchy, but does not navigate thru
>>>>> nodes of
>>>>> which the requested node is not a hierarchy member)
>>>>> 3. method 2 node collection, URI method (subset of nodes required
>>>>> are in requested node, the rest must be obtained by recursively
>>>>> navigating based on parent hierarchy nodes of which requested
>>>>> node is not a member)
>>>>> 4. method 2 node collection, ancestor method (this is the
>>>>> algorithm
>>>>> currently in section 3.2 bullets and need to recursively
>>>>> navigate thru all parent nodes regardless of whether requested
>>>>> node is a member of the hierarchy or not.)
>>>>>
>>>>> These 2 choices of node collection are implicit in the DAG problem
>>>>> definition and are not currently explained in the document and I
>>>>> believe need to be. i.e. a DAG is the result of a set of
>>>>> hierarchies (as defined above) being layed across a set of
>>>>> resources. i.e. it is the result of a set of explicit relations
>>>>> being applied between pairs of nodes. The "choice" is whether to
>>>>> retain the "history" of why those relations were applied (i.e. the
>>>>> direct relations) or not. If you don't then additional, indirect,
>>>>> extraneous relations automatically appear and there is no way
>>>>> distinguish between them and the direct relations, at least in the
>>>>> "general" or "ancestor" case. In the URI case, the direct and
>>>>> indirect relations are always present and may be used or not as a
>>>>> matter of choice.
>>>>>
>>>>> The choice of ancestor or URI method for node identification is
>>>>> simply whether URI "can" be used and whether URI is "desired" to
>>>>> be used. Functionally, URI will produce the same results.
>>>>>
>>>>> Thanks,
>>>>> Rich
>>>>>
>>>>>>
>>>>>> Daniel;
>>>>
>>>>
>>>>
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