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Subject: Re: [xacml] Possible Issue: XACML 3.0 WD 9 - 2 questions on Obligation

Hi Erik,

Thanks for the feedback and attempted clarification on AttributeValueType :).  I admit I am still a little confused, let me try to explain. I think the problem is that a definitive example is needed. Here is my perspective: A typical attribute in the RequestContext has the following form:

<Attributes Category="abc">
  <Attribute AttributeId="def" Issuer="ghi" IncludeInResult="jkl">
    <AttributeValue DataType="mno"
      >content data</AttributeValue>

(Couple points worth noting are that DataType has moved from being an attribute of Attribute in XACML 2.0 to being an attribute of AttributeValue in XACML 3.0., also that IncludeInResult is new in 3.0, and Category is expanded in 3.0 to be general, from the SubjectCategory special case from 2.0)

Presumably, all the attributes in the response sent by IncludeInResult appear in this same form in the Response.

The first additional case we addressed was MissingAttributeDetail, section 5.56, which appears to come back in the following form:

  <MissingAttributeDetail Category="abc" AttributeId="def" DataType="mno">
      >content data</AttributeValue>

This has essentially the same form as the other attributes, except:
  • Category is pushed down so it now appears alongside AttributeId etc.
  • DataType is above <AttributeValue> as it was in XACML 2.0
I am ok w those differences, since an AttributeValue may not be returned, in general, because, after all, the point is that it is "missing" and the PDP may tell the PEP what dataType is needed, it probably is not going to say what value to provide. However, and empty AttributeValue w DataType attribute might be an improvement.

Also, I am satisfied with pushing down Category into the MissingAttributeDetail, because the StatusDetail can hold multiple of these elements and there is not reason why they would all have the same Category, which is unlike the case on Input, and to some degree IncludeInResult as well.

With that context in mind, what I am "expecting" to see for AttributeAssignment is something along the following lines:

<Obligation ObligationId="123">
  <AttributeAssignment Category="abc" AttributeId="def" Issuer="ghi">
    <AttributeValue DataType="mno"
      >do this and that</AttributeValue>

I have not found any examples to confirm the above "expectation", so I have been relying on interpreting the xml, which is the reason for my original question.

From the meeting minutes, I see the TC agreed w your suggestion to include Category as optional, which seems fine to me.

So, all that remains in my mind is straightening out what is actually returned. It sounds from your description that
  • "AttributeAssignment has the same content as AttributeValueType, except that the XML attribute AttributeId is required"
I apologize for being  picky, but  with the absence of  examples,  I still find this sentence difficult to parse in a way that makes sense. I interpret "content" as "child", so in this case if I take the first part of the sentence literally, AttributeAssignment "replaces" AttributeValue, so there is no "AttributeValue" and it just has the text content, no contained elements.

Now the second part of the sentence says that "except that the XML AttributeId is required", which I interpret that AttributeId is attribute of AttributeAssignment. Finally, w decision for optional Category, we would have:

<Obligation ObligationId="123">
  <AttributeAssignment Category="abc" AttributeId="def" DataType="mno"
      >do this and that</AttributeAssignment>

Is this correct?

If so, then I guess my comment is why the need to squeeze out the AttributeValue element? Also, if it can be squeezed out why is it there in the first place?

Bottom line: I think the reason I am still confused it that there appears to be some non-intuitive behavior, which appears somewhat arbitrary, possibly because AttributeValue may be functionally extraneous, which doesn't bother me, and even if it is, my recommendation is that we use it consistently and not arbitrarily squeeze it out.

Also, might want to consider "Issuer" in the AttributeAssignment as well in case, policy designers want to distinguish where Obligations are coming from, at a finer granularity than just "the PDP".


Erik Rissanen wrote:
49C1DFFF.7080600@axiomatics.com" type="cite">Hi Rich,

I presume you are referring to the following schema fragment:

        <xs:element name="AttributeAssignment" type="xacml:AttributeAssignmentType"/>
        <xs:complexType name="AttributeAssignmentType" mixed="true">
                <xs:complexContent mixed="true">
                        <xs:extension base="xacml:AttributeValueType">
                                <xs:attribute name="AttributeId" type="xs:anyURI" use="required"/>

This means that an AttributeAssignment has the same content as AttributeValueType, except that the XML attribute AttributeId is required. Like this:

<AttributeAssignment AttributeId="urn:....:foo" DataType="urn:...:bar">
  some value here

We want to declare the XML attribute, although xs:anyAttribute is already allowed, since without the declaration the AttributeId is not _required_.

I haven't thought about the category for attributes in obligations. I have thought them as parameters of the obligation, not parts of the request. But I see the point. What about making the Category an optional XML attribute? That way it won't "pollute" those obligations which just contain obligation parameters, but it will still be possible to return parts of the request.

Best regards,

Rich.Levinson wrote:
While reviewing where we have ended up with the handling of Obligation elements in 3.0, I have 2 questions which I am unable to resolve based on my reading of the text (question 2 contains a possible issue of functionality, question 1 might just be clarification either by response to this email or by issue  for more explanatory info in the text):

   1. AttributeId in Obligation in Response: In section 5.41,
      AttributeAssignmentExpression, it says:
          * "It SHALL contain an AttributeId and an expression which
            SHALL by evaluated into the corresponding attribute value."
          * Presumably, this means that these two items will be what
            the PDP puts into the Obligation element that is put into
            the Response. This interpretation is also in agreement, I
            believe, with the description of this element in section 5.39:
                o "The expressions SHALL be evaluated by the PDP to
                  constant <AttributeValue> elements, which shall be
                  the attribute assignments in the <Obligation>
                  returned to the PEP. "
          * Presumably the two items above (AttributeValue,
            AttributeId) are then put by the PDP into the
            AttributeAssignment element (section 5.36) which is child
            to the Obligation (section 5.34)
          * Here is my basic question on section 5.36, which may be
            simply that I do not understand the mechanics of the
            extension element in the schema: it appears on lines
            2543-2546 that AttributeId might be defined here as an
            attribute of AttributeValue:
                o "

                        <xs:extension base="xacml:AttributeValueType">

                           <xs:attribute name="AttributeId"



                o So, that's the 1st part of the question. Is this the
                  same AttributeId identified in section 5.41, and
                  does it show up in the output Obligation as an
                  attribute of the AttributeAssignment element or of
                  the AttributeValue element? (It appears based on the
                  above that it might be the latter, if not please
                o If it is the an attribute of AttributeValue, the 2nd
                  part of the question is does this not kind of
                  violate section 5.31 AttributeValue, because this
                  AttributeId would presumably now be part of the
   2. (2nd question) Should we include the "Category" in the
      Obligation (probably not because that would apply to all
      AttributeAssignments) or preferably in the AttributeAssignment
      (assuming the AttributeId is already there from question 1)?
          * The reason for asking is that it does not seem
            unreasonable that in many cases the AttributeId assigned
            to the Obligation/AttributeAssignment will be the same
            AttributeId used to pull an attribute out of the Request.
            Granted, it doesn't have to be, but let's assume that is
            what some people might want to do.
          * Assuming people want to do this, we now run into the same
            ambiguity that led to the addition of Category to
            MissingAttributeDetail (section 5.56), namely that if the
            PEP needs to know how to correlate the returned attributes
            with the input request, then both AttributeId and Category
            are needed, in general.


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