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Subject: Re: [xacml] Re: XACML's limitations in the access control for XMLdocuments use case - AW: AW: [xacml] CD-1 issue #11: strictness of xpathdefinition
Hi Paul,
See some comments inline.
Best regards,
Erik
Tyson, Paul H wrote:
> No one has produced an actual use case that requires regexp on xpath resource-ids to solve. I am not inclined to jump to this sort of solution. I have a lot of experience writing xpath expressions for xslt transformations, so I am skeptical when anyone suggests additional functionality is required in this area, that is not already provided by well-established standards.
>
> I still plan to start some wiki pages on these topics, but I want to introduce some other aspects of this discussion.
>
> 1. Part of the problem is that XACML overloads the concept of "resource-id" when it can be used actually as a "resource-selector" in multi-resource request for XML resources. This causes the actual resource-id that is used during evaluation to be different than the initial resource-id (it has been "expanded" to describe the exact node). I believe this is a defect in the specification, which should be remedied in any case. You face this problem when you want to write (as Jan does) rules involving the string value of the resource-id. (I still don't understand the motivation for writing these sorts of rules, but that's a different matter.)
>
Yes, I agree. If I understand you correctly, this is the exact same
issue I am thinking of when I say that the multiple resource profile
"breaks the XACML assumption that the <Request> describes a single
attempted access to a single resource".
> 2. Related to the above point, there seems to be a gap in the current multi-resource specification, because it is not clear how the response identifies the xml node for each decision. If PEP asks for decisions on "//*[@id=('foo','bar','baz')]" (i.e., elements whose id attribute is 'foo', 'bar', or 'baz'), what should be the respective values of the resource-ids in the response? They could be "//*[@id='foo']", "//*[@id='bar']", "//*[@id='baz']". Or they could be "/chapter[1]/section[3]/para[1]", "/chapter[2]", "/chapter[2]/section[1]/fig[1]". Assuming the PEP has xpath processing capabilities, it really shouldn't matter. But the XACML spec should at least say something like "the returned resource-id shall be an xpath expression which, when evaluated against the original xml content, returns exactly (and only) the node on which the decision was issued".
>
This behavior is already required by the current specification, but
could perhaps be stated more explicitly. The PDP will return the
resource-id attribute specified in the individual request if the
"IncludeInResult" attribute has been set to "true". And the multiple
resource profile already requires that for each individual request the
resource-id must consist of an XPath expression which matches exactly
one node. The combined effect of this is the behavior you describe above.
> 3. Much of this discussion centers around the conceptual model of multi-resource requests. The spec says these are to be treated as a series of individual requests, and describes the required context of each derived request. This model is normative only in concept, not for implementation--that is, a PDP must issue decisions as if this model had been followed. The MR spec says "This Profile does NOT REQUIRE that the implementation of the evaluation of a request for access to multiple resources conform to the preceding model or that actual Individual Resource Requests be constructed." (section 2) Therefore, the behavior of any rule evaluation that depends on a particular implementation of multi-resource requests is out of scope (and unspecified). I believe the discussion of xpath resource-id rules falls into this category. (I also believe the model of multi-resource decision evaluation needs to be defined better.)
>
Sorry, but I don't understand this point. But I do think it is relevant
to discuss whether the spec can be implemented in any efficient manner,
and this can affect what the specification should be like.
> --Paul
>
>
>
>> -----Original Message-----
>> From: Jan Herrmann [mailto:herrmanj@in.tum.de]
>> Sent: Thursday, October 01, 2009 07:04
>> To: 'Rich.Levinson'
>> Cc: xacml@lists.oasis-open.org
>> Subject: AW: [xacml] Re: XACML's limitations in the access
>> control for XML documents use case - AW: AW: [xacml] CD-1
>> issue #11: strictness of xpath definition
>>
>> Hi Rich,
>>
>> I highly agree with what you said in this mail. It seems that
>> your use case goes a bit further then the one I am thinking
>> of. Let me try to identify the common and varying parts of
>> our use cases.
>>
>> If I understand you correctly you are not only thinking about
>> how the resource-id values of the individual decision
>> requests in the xml use case have to look like. You are
>> further having the file system and URL resource use case in
>> mind. This is something I have never thought about so far.
>>
>> Further it seems that you are trying to represent the whole
>> resource through and only through URIs in one decision
>> request. That's also somehow different to the use case I have
>> in mind, as in my scenario the resource (the xml doc) is
>> always included under <content> as it is and the question of
>> representation is always reduced to how to represent the
>> resource-id value that must match exactly one node under content.
>>
>> I think one important task is to try to identify the common
>> or relating aspects of the different use cases and where they
>> differ or where they are independent.
>>
>> I agree that in issue 11 the namespace problem was not
>> handled at all. Thus some little extra work is needed.
>>
>> I further agree that it would be beautiful to have the same
>> style how to define rules for different kind of resources if
>> possible. Thus I fully share your proposal to add an
>> alternative for representing nodes (or whatsoever) as
>> resource-id-values or in general.
>>
>> As far as I understand the Clark notation it is simply a
>> substituted form where prefixes are replaced by the
>> namespaces bound to them. For my use case this would work
>> perfectly well. The question is if you want to try to force
>> the policy writer to follow this syntax when defining the
>> resource-id match in its rule. Further if you think of an
>> AttributeSelector that can concatenate resource-id with an
>> offset this implies that the AttributeSelector implementation
>> must be able to deal with the clark syntax to :-(
>>
>>
>> In my scenario there is another possible alternative (as
>> mentioned in the mail submitted two hours ago):
>> You could use a special reg-exp-On-XPath-strings function
>> that is namespace aware and substitutes the prefixes
>> correspondingly before doing the common reg-expr matching
>> stuff on the resource-id attribute. This
>> reg-exp-On-XPath-strings function is the function to test the
>> resource-id values only.
>> Does your use cases require more functions that work on a URI
>> based representation of individual resources?
>>
>> Below you'll find further comments to your questions in an
>> earlier mail.
>> Basic conclusion of the comments below:
>> allow to represent the resource in xml or through a set of
>> attribute/value pairs (if can be shown that this realy brings
>> advantages).
>>
>> Looking forward to further discussions and comments.
>>
>> Best regards
>> Jan
>>
>>
>>
>>
>>
>> ________________________________________
>>
>> Jan Herrmann
>> Dipl.-Inform., Dipl.-Geogr.
>>
>> wissenschaftlicher Mitarbeiter
>>
>> Technische Universität München
>> Institut für Informatik
>>
>> Lehrstuhl für Angewandte Informatik / Kooperative Systeme
>>
>> Boltzmannstr. 3
>> 85748 Garching
>>
>> Tel: +49 (0)89 289-18692
>> Fax: +49 (0)89 289-18657
>> www11.informatik.tu-muenchen.de
>> ________________________________________
>>
>>
>>
>>> -----Ursprüngliche Nachricht-----
>>> Von: Rich.Levinson [mailto:rich.levinson@oracle.com]
>>> Gesendet: Montag, 28. September 2009 22:40
>>> An: Erik Rissanen
>>> Cc: XACML TC
>>> Betreff: Re: [xacml] Re: XACML's limitations in the access
>>>
>> control for XML
>>
>>> documents use case - AW: AW: [xacml] CD-1 issue #11:
>>>
>> strictness of xpath
>>
>>> definition
>>>
>>> Hi Erik,
>>>
>>> The intent of the proposal is not to replace or be better
>>>
>> than XPath,
>>
>>> but to be an "alternative representation" for node identification as
>>> described in section 2.0 of the profile, which if we included in the
>>> profile as suggested in section 2.2.1, presumably would then be a
>>> "recommended alternative representation".
>>>
>>> The reason for the suggestion was to address the
>>>
>> requirements specified
>>
>>> in issue 11, which contained a recommended syntax that did not
>>> incorporate namespaces. By using the Clark notation for the
>>>
>> namespaces,
>>
>>> the syntax in issue 11 can be directly incorporated to the
>>>
>> URI scheme as
>>
>>> described in the proposal.
>>>
>>> Once the syntax is in place then the same kinds of regexp-scoped
>>> Policy's can be written for XML nodes as for file system and URL
>>> resources.
>>>
>>> Assuming the syntax and proposal is correct, it may be a useful
>>> alternative representation in some situations, particularly
>>>
>> where it may
>>
>>> be an objective to identify all resources w URIs, and/or
>>>
>> where the mixed
>>
>>> XACML/XPATH syntax is a concern wrt Policy specification.
>>>
>>> Thanks,
>>> Rich
>>>
>>>
>>> Erik Rissanen wrote:
>>>
>>>> Hi Rich,
>>>>
>>>> Some of the reasons why an XPath approach could be better are:
>>>>
>>>> 1. XPath contains many functions and other capabilities,
>>>>
>> which might
>>
>>>> not be as easily available in the URI based approach.
>>>>
>>>> 2. The TC would avoid the effort to define the URI
>>>>
>> approach. We would
>>
>>>> need to improve the xpath approach instead, but I suspect that the
>>>> effort is smaller since we can reuse so much from xpath,
>>>>
>> compared with
>>
>>>> a wholly new URI based approach.
>>>>
>>>> 3. It is likely that an XML resource is already available
>>>>
>> in XML form,
>>
>>>> so an xpath implimentation can be applied to it directly,
>>>>
>> while the
>>
>>>> URI approach requires a transformation, which could
>>>>
>> degrade performance.
>>
>>>> Note that it is not true that the whole XML has to be repeated for
>>>> each resource since multiple <Attributes> elements are
>>>>
>> not required
>>
>>>> with the xpath approach, and with XACML 3.0 it is
>>>>
>> possible to reuse
>>
>>>> the same <Content> document for all the multiple queries.
>>>>
>>>> Best regards,
>>>> Erik
>>>>
>>>> Rich.Levinson wrote:
>>>>
>>>>> Hi Jan, et al,
>>>>>
>>>>> I have had a busy week and not been able to respond until now,
>>>>> however, looking over all the subsequent emails to the
>>>>>
>> one to which
>>
>>>>> this is a response (
>>>>> http://lists.oasis-open.org/archives/xacml/200909/msg00081.html
>>>>> ), it appears to me that there are still unresolved
>>>>>
>> issues, and from
>>
>>>>> my perspective, there are some assertions made, with which I
>>>>> disagree, about AttributeDesignators, which I thought my
>>>>>
>> suggested
>>
>>>>> URI scheme would address, but apparently it either needs further
>>>>> explanation or I am missing something that I have not
>>>>>
>> yet understood.
>>
>>>>> In any event I would very much like to determine whether these
>>>>> assertions are true or false in order that the TC be of
>>>>>
>> a single mind
>>
>>>>> when comparing the capabilities of AttributeSelectors and
>>>>> AttributeDesignators.
>>>>>
>>>>> The assertion with which I disagree is that the
>>>>>
>> AttributeDesignators
>>
>>>>> cannot do what the AttributeSelectors can do because the
>>>>> AttributeDesignators lose the hierarchical structure.
>>>>>
>> My response is
>>
>>>>> that if you don't throw away the hierarchical structure when
>>>>> creating your AttributeDesignators then this
>>>>>
>> perceived problem does
>>
>>>>> not exist.
>>>>>
>> For the XML use case:
>> I can imagine that it is possible to rebuild the semantics that are
>> expressed through the structure of nodes through an
>> appropriate naming of
>> the attributes. But it seems to be very complicated and I
>> can't find the
>> advantages of transforming an originally xml encoded resource in uris
>> without benefits. Further this will imply special functions
>> working on the
>> chosen naming-schema see below.
>> Why should one try to avoid AttributeSelectors at all?
>>
>>
>>
>>>>> If I am wrong about this, I will accept that, however, I do not
>>>>> believe that my approach to the AttributeDesignators has been
>>>>> considered on its merits yet, and I will try to be
>>>>>
>> totally explicit
>>
>>>>> in this email, and I will show how I think Jan's
>>>>>
>> proposed solution
>>
>>>>> can be completely done using only AttributeDesignators and regexp
>>>>> string matching.
>>>>>
>>>>> Having been thru some lengthy discussions earlier this
>>>>>
>> year on the
>>
>>>>> hierarchical profile, I became quite sensitive to the node naming
>>>>> issue, and one of the results of those earlier
>>>>>
>> discussions was that
>>
>>>>> if hierarchical URIs are used to name nodes, that these
>>>>>
>> names contain
>>
>>>>> within them the navigation necessary to locate the node, so that
>>>>> using these names outside of an XML document does not lose the
>>>>> structural relationships.
>>>>>
>>>>> Using James Clark's universal name syntax
>>>>>
>> ("{namespace}elementname"
>>
>>>>> http://www.jclark.com/xml/xmlns.htm) combined with a transform to
>>>>> replace the xml document with a list of name/value pairs
>>>>>
>> (there are
>>
>>>>> several XML to JSON xslt transformers available free,
>>>>>
>> which I expect
>>
>>>>> could readily be adapted to produce name/value pairs in
>>>>>
>> the format
>>
>>>>> below), where each element and attribute is identfied by its full
>>>>> path expressed as universal element names. For example,
>>>>>
>> assuming the
>>
>>>>> document you gave as an example had a namespace = "foo":
>>>>>
>>>>> <objects xmlns:="foo">
>>>>> <book>
>>>>> <title>xxx</title>
>>>>> <author>Bob</author>
>>>>> <id>100</id>
>>>>> <price>30</price>
>>>>> <book-content>.....</book-content >
>>>>> <book>
>>>>> <book>
>>>>> <title>yyy</title>
>>>>> <author>Alice</author>
>>>>> <id>200</id>
>>>>> <price>80</price>
>>>>> <book-content >...</book-content >
>>>>> <book>
>>>>> </objects>
>>>>>
>>>>> The above document would first be transformed to the
>>>>>
>> following set of
>>
>>>>> name value pairs (ignoring whitespace):
>>>>> /{foo}objects = ""
>>>>> /{foo}objects/{foo}book[1] = ""
>>>>> /{foo}objects/{foo}book[1]/{foo}title = "xxx"
>>>>> /{foo}objects/{foo}book[1]/{foo}author = "Bob"
>>>>> /{foo}objects/{foo}book[1]/{foo}id = "100"
>>>>> /{foo}objects/{foo}book[1]/{foo}price = "30"
>>>>> /{foo}objects/{foo}book[1]/{foo}content = "..."
>>>>> /{foo}objects/{foo}book[2] = ""
>>>>> /{foo}objects/{foo}book[2]/{foo}title = "yyy"
>>>>> /{foo}objects/{foo}book[2]/{foo}author = "Alice"
>>>>> /{foo}objects/{foo}book[2]/{foo}id = "200"
>>>>> /{foo}objects/{foo}book[2]/{foo}price = "80"
>>>>> /{foo}objects/{foo}book[2]/{foo}content = "..."
>>>>>
>>>>> The next step is to define resources, which for this use
>>>>>
>> case would
>>
>>>>> be done based on multiple resource profile, where we would have 2
>>>>> resources, using Erik's shorthand:
>>>>> <Resource>resource-id=/{foo}objects/{foo}book[1]</Resource>
>>>>> <Resource>resource-id=/{foo}objects/{foo}book[2]</Resource>
>>>>>
>>>>> The next step is to create xacml attributes for these
>>>>>
>> resources using
>>
>>>>> the full universal names as AttributeIds (again w some
>>>>>
>> shorthand),
>>
>>>>> resulting in the following 2 requests:
>>>>> (Note: since AttributeId requires anyURI datatype, the following
>>>>> percent-encoding must be applied to the AttributeId values:
>>>>>
>>>>> * { -> %7B
>>>>> * } -> %7D
>>>>> * [ -> %5B
>>>>> * ] -> %5D )
>>>>>
>>>>>
>>>>> <Request>
>>>>> <Subject>subject-id="Bob"</Subject>
>>>>> <Resource>
>>>>> <Attribute>AttributeId="resource-id"
>>>>> value="/{foo}objects/{foo}book[1]"</Attribute>
>>>>>
>>>>>
>> <Attribute>AttributeId="/%7Bfoo%7Dobjects/%7Bfoo%7Dbook%5B1%5D
>> /%7Bfoo%7Dti
>>
>>> tle"
>>>
>>>>> value = "xxx"</Attribute>
>>>>>
>>>>>
>> <Attribute>AttributeId="/%7Bfoo%7Dobjects/%7Bfoo%7Dbook%5B1%5D
>> /%7Bfoo%7Dau
>>
>>> thor"
>>>
>>>>> value = "Bob"</Attribute>
>>>>>
>>>>>
>> <Attribute>AttributeId="/%7Bfoo%7Dobjects/%7Bfoo%7Dbook%5B1%5D
>> /%7Bfoo%7Did
>>
>>> "
>>>
>>>>> value = "100"</Attribute>
>>>>>
>>>>>
>> <Attribute>AttributeId="/%7Bfoo%7Dobjects/%7Bfoo%7Dbook%5B1%5D
>> /%7Bfoo%7Dpr
>>
>>> ice"
>>>
>>>>> value = "30"</Attribute>
>>>>>
>>>>>
>> <Attribute>AttributeId="/%7Bfoo%7Dobjects/%7Bfoo%7Dbook%5B1%5D
>> /%7Bfoo%7Dco
>>
>>> ntent"
>>>
>>>>> value = "..."</Attribute>
>>>>> </Resource>
>>>>> </Request>
>>>>>
>>>>> <Request>
>>>>> <Subject>subject-id="Bob"</Subject>
>>>>> <Resource>
>>>>> <Attribute>AttributeId="resource-id"
>>>>> value="/{foo}objects/{foo}book[2]"</Attribute>
>>>>>
>>>>>
>> <Attribute>AttributeId="/%7Bfoo%7Dobjects/%7Bfoo%7Dbook%5B2%5D
>> /%7Bfoo%7Dti
>>
>>> tle"
>>>
>>>>> value = "yyy"</Attribute>
>>>>>
>>>>>
>> <Attribute>AttributeId="/%7Bfoo%7Dobjects/%7Bfoo%7Dbook%5B2%5D
>> /%7Bfoo%7Dau
>>
>>> thor"
>>>
>>>>> value = "Alice"</Attribute>
>>>>>
>>>>>
>> <Attribute>AttributeId="/%7Bfoo%7Dobjects/%7Bfoo%7Dbook%5B2%5D
>> /%7Bfoo%7Did
>>
>>> "
>>>
>>>>> value = "200"</Attribute>
>>>>>
>>>>>
>> <Attribute>AttributeId="/%7Bfoo%7Dobjects/%7Bfoo%7Dbook%5B2%5D
>> /%7Bfoo%7Dpr
>>
>>> ice"
>>>
>>>>> value = "80"</Attribute>
>>>>>
>>>>>
>> <Attribute>AttributeId="/%7Bfoo%7Dobjects/%7Bfoo%7Dbook%5B2%5D
>> /%7Bfoo%7Dco
>>
>>> ntent"
>>>
>>>>> value = "..."</Attribute>
>>>>> </Resource>
>>>>> </Request>
>>>>>
>>>>> All the above processing to create the requests is done in the
>>>>> ContextHandler, then the requests are submitted one at a
>>>>>
>> time to the
>>
>>>>> PDP.
>>>>> Now the rule that gets applied to each of these requests is the
>>>>> following:
>>>>>
>>>>> <Rule effect=Deny>
>>>>> Target:
>>>>> reg-exp-string-match(resource-id,
>>>>>
>> /{foo}objects/{foo}book\[\d+\]
>>
>>>>> Condition:
>>>>> AttributeDesignator(AttributeId =
>>>>> function:string-concatenate(resource-id,
>>>>>
>> /%7Bfoo%7Dprice) > 50 and
>>
>>>>> AttributeDesignator(AttributeId =
>>>>> function:string-concatenate(resource-id, /%7Bfoo%7Dauthor) =
>>>>> AttributeDesignator(subject-id)
>>>>> </Rule>
>>>>>
>>>>> Unless I am mistaken, all the logic and structure is
>>>>>
>> retained and it
>>
>>>>> has been done purely w AttributeDesignators and regexp.
>>>>>
>> I think i can follow your approach and agree that this
>> explicitly represents
>> the xml resource through URIs.
>> Probs:
>> - things like ../../ will be hard to handle
>> - in the geo use case we have an geometry data type. This
>> datapye is defined
>> by the following xml code:
>>
>> <gml:Polygon srsName="http://www.opengis.net/../epsg.xml#43";>
>> <gml:outerBoundaryIs>
>> <gml:LinearRing>
>> <gml:coordinates decimal="." cs="," ts=" ">-120.000000,65.588264
>> ...-120.000000,65.588264
>> </gml:coordinates>
>> </gml:LinearRing>
>> </gml:outerBoundaryIs>
>> </gml:Polygon>
>>
>> Now assume you try to define a rule, following your approach,
>> in which you
>> use a pointer to a polygon element in the decision request's
>> content element
>> (e.g. a polgon representing the location of a building):
>> In very dirty/wrong XACML this will look like this:
>> <Rule effect=permit>
>> <Target>
>> subject-id==Alice
>> reg-exp-string-match(resource-id, /{foo}objects/{foo}building\[\d+\]
>> <Condition>
>> <Apply FunctionId=within>
>> <ExtendedAttributeSelector Category=resource>
>> <concat>
>> <AttributeDesigntor>resource-id
>> <AttributeValue>/%7Bfoo%7Dlocation/%7Bfoo%7DPolygon
>> </concat>
>> <AttributeValue DataType=Geometry>
>> <Polygon>...defining the area of the USA </Polygon>
>> </AttributeValue>
>> </Apply>
>> </Condition>
>> </Rule>
>>
>> So far no probs. Let's have a have a closer look at the
>> AttributeSeletor,
>> responsible for instantiating an attribute of datatype
>> Geometry. It will
>> have to go through all the URIs representing the resource and find the
>> relevant ones in order to instantiate the geometry attribute.
>> This can off
>> course be implemented but the question is why to "flatten" an
>> xml doc, if
>> afterwards, you need to rebuild parts of it.
>> This makes the AttributeSelector implementation unneccesarely
>> complicated.
>>
>> I think what needs to be analysed is:
>> - What are the advantages to transform the xml resource
>> completely into uris
>> or Attribut/Value pairs respectively?
>> - What are the disadvantages of doing this?
>>
>> The approach of leaving the xml resource as it is in the
>> decision request
>> and just adding a resource-id/value pair pointing to one node
>> implies that
>> you will have to use AttributeDesignators and
>> AttributeSelectors in your
>> rules. Is this a disadvantage? It seems that you are trying
>> to avoid the
>> selector at all. But I can't follow why.
>>
>> However if it can be shown that it brings advantages to encode an xml
>> resource in the decision request only through Attribute/Value
>> pairs that I
>> would support this as an legal option that should be added to
>> the profile.
>> Of course this must bring advantages. Whithout advantages
>> this will just
>> introduce another way of how to define the same rules for now reason.
>>
>>
>>
>>
>>
>>
>>>>> Assuming the above is correct, then the points I made about the
>>>>> advantages over XPath (for an enterprise looking to use
>>>>>
>> only URIs to
>>
>>>>> identify attributes):
>>>>>
>>>>> 1. The XML document does not need to be passed in with
>>>>>
>> the request.
>>
>>>>> There is no node collection, only string operations.
>>>>>
>> If I may concretise:
>> Case 1.
>> In the global request you will have a content element
>> containing the xml
>> resource and an scope attribute describing a subset of this
>> node collection
>> that will be subject to the access control process.
>> Based on this the PDP or Contexthandler will derive the
>> individual decision
>> requests. Here the xml resource could be transformed as you
>> described above
>> and thus you will afterwards only have attribute/value pairs.
>> Case2:
>> The PEP can directly submits "already-transformed" global
>> decision request
>> where the xml resource that is "normally" under <content> is
>> replaced by a
>> set of Attribute/Value pairs. Further the resource-id and
>> scope must specify
>> a set of these Attribute-Names. Based on this the PDP or
>> Contexthandler will
>> derive the individual decision requests. The individual
>> decision requests
>> will still contain the complete set of Attribute/Value pairs
>> that represent
>> the xml resource and further the resource-id value will be
>> equal to one of
>> these Attribute-Names.
>>
>>
>>
>>
>>>>> 2. For very large XML documents, say a catalog of
>>>>>
>> 10,000 books, each
>>
>>>>> book is processed individually independent of the
>>>>>
>> other books, as
>>
>>>>> compared to the XPath case, where one might expect the whole
>>>>> document has to get parsed for each of the 10,000 individual
>>>>> requests.
>>>>>
>> This is only true if you don't have content dependant rules.
>> e.g. assume you
>> have a rule that says permit access to books if none of the
>> other books is
>> from the same author. Nevertheless I can imagine that in
>> average less data
>> has to be parsed... On the other side there might be an overhead of
>> determining which data.
>> Again the question: What are the advantages of transforming
>> the resource
>> completely into URIs. I think if this is the central point a
>> closer analysis
>> is needed.
>>
>>
>>
>>>>> 3. There is no paradigm shifting, or what I believe
>>>>>
>> was referred to
>>
>>>>> in the discussion as "shifting semantics between
>>>>>
>> XPath and XACML
>>
>>>>> in terms of representing the policies.
>>>>>
>> If i understand you correctly you mean that all access right
>> semantic will
>> be expressed in xacml. That is necessarily true as you don't
>> have any xml
>> resource in the request anymore and thus xpath predicates
>> can't be defined
>> anymore. Is this an advantage? Clearly this reduces the
>> options how the same
>> rule can be defined in xacml and might therefore simplify a
>> are-two-rules-equal test. Note that this could also be achieved if you
>> disallow xpath with predicates in xacml. Thus this issue can
>> be discussed in
>> general.
>> My experience in using a mixture of xpath predicates and xacml where
>> necessary (i.e. where the ac semantics can't be expressed
>> through xpath
>> predicates) helps defining shorter and more readable rules. I
>> would leave it
>> open to the policy administrator if he implements the
>> semantics through
>> xpath predicates or xacml functions. Maybe a best practise study could
>> analyse this topic (next to others). In general I think such
>> a document
>> might be very helpful as soon as the 3.0 specs are
>> standardised in order to
>> make it easier for users to use XACML
>>
>>
>>
>>
>>>>> Again, assuming the above is correct, I am not assuming
>>>>>
>> this will be
>>
>>>>> desirable for everyone, however there may very well be
>>>>>
>> organizations
>>
>>>>> for whom the advantages of this approach are decisive.
>>>>>
>>>>> A couple other points are that
>>>>>
>>>>> * the "unsightliness" of the AttributeIds and the
>>>>> AttributeDesignators can be "covered" up by policy
>>>>>
>> tools that
>>
>>>>> facilitate defining policies based on XML Schemas,
>>>>>
>> and can keep
>>
>>>>> all the encoding details transparent to the policy
>>>>>
>> designers.
>>
>>
>> i agree
>>
>>
>>>>> * the issue about basing policies on the structure of
>>>>>
>> XML documents
>>
>>>>> is a legitimate concern, however, if structure of documents
>>>>> change, then a legitimate case could probably made that the
>>>>> namespace associated with that structure should
>>>>>
>> also change, which
>>
>>>>> would mean the policy tools would need to be able
>>>>>
>> to facilitate
>>
>>>>> upgrading of policies to new namespaces based on
>>>>>
>> new revs of the
>>
>>>>> schemas.
>>>>>
>>>>> Comments and suggestions welcome.
>>>>>
>>>>> Thanks,
>>>>> Rich
>>>>>
>>>>>
>>>>
>>>>
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