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Subject: RE: [xacml] [CR] AttributeSelectorIndirect
On Fri, 6 Sep 2002, Daniel Engovatov wrote:
> My guess that in your example what you really want to use
> are functions string-member-of and integer-member-of.
No. The *Match function semantics have that capability. You specify with
the MatchID the function that does the individual comparisons. This
approach lets you specify predicates that aren't just based on equality,
such as some regular expression matching function.
-Polar
> In this case if the selector returns more then one value, at
> least one should match. It fits the current type model.
>
> For integer-member-of - value returned by the selector will
> be converted to integer value and numerical comarison will be used.
> Result will be INDETERMINATE if the conversion could not be
> performed.
>
> daniel;
>
> ---------------------
> <ResourceMatch MatchId="function:string-equal">
> <AttributeSelector RequestContextPath="/a/b/c/text()">
> <AttributeValue>bb1</AttributeValue>
> </ResourceMatch>
>
> The first attribute selector may return a sequence of primitive types
> (e.g.
> bb1 and bb2). Then what is the semantics of the function:string-equal?
> Does
> that compare each of the return value of the attribute selector with
> "bb1"?
>
> What if function:integer-equal is used?
>
> <ResourceMatch MatchId="function:integer-equal">
> <AttributeSelector RequestContextPath="/a/b/@b1">
> <AttributeValue>100</AttributeValue>
> </ResourceMatch>
>
> Comparison is done based on numeric comparison?
>
> Michiharu Kudo
>
> IBM Tokyo Research Laboratory, Internet Technology
> Tel. +81 (46) 215-4642 Fax +81 (46) 273-7428
>
>
>
>
>
>
> Polar Humenn
>
> <polar@syr.edu> To: Michiharu
> Kudoh/Japan/IBM@IBMJP
>
> cc: XACML
> <xacml@lists.oasis-open.org>
>
> 2002/09/06 22:14 Subject: Re: [xacml]
> [CR] AttributeSelectorIndirect
>
>
>
>
>
>
>
>
>
>
>
> Hi Michiharu,
>
> Comments are inline.
>
> On Fri, 6 Sep 2002, Michiharu Kudoh wrote:
>
> >
> > Polar
> >
> > I have a couple questions.
> >
> > 1. How to mandate a returned data from the attribute selector to be a
> > sequence of a specific type? Are you suggesting to specify DataType
> > attribute in the attribute selector element?
>
> You always must apply a function to any result of an attribute selector.
> That function specifies the types of its formal parameters, and
> therefore
> implies the type of the attribute selector. You said so yourself for
> AttributeValues.
>
> > 2. I am not clear on how to specify resource match using
> > function:string-equal. Is the following policy fragment correct if the
> > attribute selector returns a sequence of a primitive type (string type
> > because function:string-equal implies that)?
> >
> > <ResourceMatch MatchId="function:string-equal">
> > <AttributeSelector RequestContextPath="/a/b/@b1/">
> > <AttributeSelector RequestContextPath="/a/b/c/text()"/>
> > </ResourceMatch>
>
> This example is wrong. The second element of a ResourceMatch must be a
> primitive value, currently an explicit AttributeValue.
>
> <ResourceMatch MatchId="function:string-equal">
> <AttributeSelector RequestContextPath="/a/b/@b1/">
> <AttributeValue>bb1</AttributeValue>
> </ResourceMatch>
>
> However, if you really want to put a "value" as the second argument, of
> which I cannot see a good argument against, it would require a SCHEMA
> CHANGE.
>
> Given that we agree with that, If you believe the /a/b/c/text() will
> return a sequence of one you would use:
>
> <ResourceMatch MatchId="function:string-equal">
> <AttributeSelector RequestContextPath="/a/b/@b1/">
> <Apply FunctionId="string-first-and-only">
> <AttributeSelector
> RequestContextPath="/a/b/c/text()"/>
> </Apply>
> </ResourceMatch>
>
> If for some reason, your resource data model is screwed up, and your
> "/a/b/c/text()" attribute selector returns a sequence of more than one
> or
> empty, you will get an Indeterminate (i.e. an error).
>
> > 3. I want to see specification examples how to use each function in
> Match
> > element and Condition element.
>
> Above is one example.
>
> > Sample XACML Contexts and policy specifications would be helpful to
> > understand how to use functions. Otherwise, I cannot have a clear
> > mapping between XPath 1.0 (and 2.0) functions and XACML functions.
>
> Is the above enough to get the point across?
>
> -Polar
>
> > Michiharu Kudo
> >
> > IBM Tokyo Research Laboratory, Internet Technology
> > Tel. +81 (46) 215-4642 Fax +81 (46) 273-7428
> >
> >
> >
> >
> >
> > Polar Humenn
> > <polar@syr.edu> To: Michiharu
> Kudoh/Japan/IBM@IBMJP
> > cc: XACML
> <xacml@lists.oasis-open.org>
> > 2002/09/05 23:01 Subject: Re: [xacml]
> [CR]
> AttributeSelectorIndirect
> >
> >
> >
> >
> >
> >
> >
> > Michiharu,
> >
> > Comments inline.
> >
> > On Wed, 4 Sep 2002, Michiharu Kudoh wrote:
> >
> > >
> > > Hi, Polar
> > >
> > > I think that the policy syntax I posted before can be consistent
> with
> the
> > > functions and data types specified in the latest draft of XACML
> standard
> > > function. (when I first proposed, there was no notion of sequence
> data
> > > type) Since XACML supports a sequence and a set data types,
> functions
> > that
> > > processes XPath expressions can be mapped to those data types.
> > >
> > > Basically XPath 1.0 defines a return type as an object data type
> > > (either node-set, boolean, number, or string). To define a mapping
> > > rule from XPath object data type to XACML sequence data type would
> be
> > > a choice, I think. The problem would be that "node-set" of XPath is
> > > different from "sequences of primitive types". It is not a sequence
> of
> > > primitive-type data but just a set of (DOM) nodes which may include
> a
> > > structured node. But if we ignore that structured node case, it
> would
> > > be easy to map node-set to "sequence of primitive type". Then the
> > > definition of <AttributeSelector> processes XPath expressions and do
> a
> > > data conversion. Examples are the following:
> > >
> > > Suppose there is a XML document:
> > > <a a1="aaa">
> > > <b b1="bb1">
> > > <c>bb1</c>
> > > </b>
> > > <b b1="bb2"/>
> > > </a>
> > >
> > > Case A:
> > > XPath expression of "/a/@a1" returns an attribute node:
> > > attribute node "a1" that contains a text node "aaa"
> >
> > I believe we mandate this to be a sequence of a specific type implied
> by
> > the function applied to it. Such as if we used
> "function:string-member-of"
> > on this result of this XPATH expression its type is implied to be a
> > sequence of xs:string, for XACML purposes.
> >
> > > Case B:
> > > XPath expression of "/a/b/@b1" returns two attribute nodes "b1":
> > > attribute node "b1" that contains "bb1"
> > > attribute node "b1" that contains "bb2"
> >
> > Again, I believe we mandate this to be a sequence of a specific type
> > implied by the function applied to it. If we used
> > "function:string-memeber-of" it would be considered a sequence of
> > xs:string containing "bb1" and "bb2".
> >
> >
> > > Case C:
> > > XPath expression of "/a/b/c/text()" returns a text node:
> > > text node that contains "xyz"
> >
> > again, same thing.
> >
> > > Above three cases indicates a natural mapping from node set to a
> sequence
> > > of primitive data types. (For simplicity, I ignore primitive data
> type
> > > here)
> >
> > I agree.
> >
> > > Case D:
> > > XPath expression of "/a/b" returns two notes:
> > > element node "b" that contains element "c" and attribute "b1"
> > > element node "b" that contains attribute "b1"
> > >
> > > In Case D, there is no natural mapping from returned node set
> because
> > > returned object is a structured node. (In XPath 1.0, there is a
> > conversion
> > > definition of structured node (as a string value), I don't think it
> fits
> > to
> > > XACML case.)
> > >
> > > One possibility would be to raise an error for Case D, or returns an
> > empty
> > > sequence without error.
> >
> > I think returning and empty sequence is a REALLY bad idea. If we
> allowed
> > this kind of thing, there is no need for a type system or any
> integrity
> to
> > the evaluation of policy against its inputs.
> >
> > If you have a node-set that is some type other than the standard types
> > that we support, you should use create a type extension and functions
> that
> > explicity know how to deal with that extension, otherwise it is an
> error
> > (which can quite possibly be handled at compile time).
> >
> > > (Anyway, policy writer must be sure that the XPath
> > > expression really returns sequence of primitive types.)
> > > Based on the above observation, the following example returns true:
> > >
> > > <ResourceMatch MatchId="function:has-string-intersection">
> > > <AttributeSelector RequestContextPath="/a/b/@b1/">
> > > <AttributeSelector RequestContextPath="/a/b/c/text()"/>
> > > </ResourceMatch>
> >
> > I thinkthe function you would use here would be
> "function:string-equal"
> > because the ResourceMatch has the semantics of applying the function
> named
> > by MatchId to the elements in the sequences to see if there is a
> match.
> >
> > -Polar
> >
> > > For example, function:has-intersection returns true because the
> first
> > > argument and the second argument has an intersection ("bb1") as a
> string
> > > value.
> > >
> > > Michiharu
> > >
> > > IBM Tokyo Research Laboratory, Internet Technology
> > > Tel. +81 (46) 215-4642 Fax +81 (46) 273-7428
> > >
> > >
> > >
> > >
> > >
> > > Polar Humenn
> > > <polar@syr.edu> To: Michiharu
> > Kudoh/Japan/IBM@IBMJP
> > > cc: XACML
> > <xacml@lists.oasis-open.org>
> > > 2002/08/30 21:47 Subject: Re: [xacml]
> [CR]
> > AttributeSelectorIndirect
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > Michiharu,
> > >
> > > Comments inline.
> > >
> > > On Fri, 30 Aug 2002, Michiharu Kudoh wrote:
> > >
> > > >
> > > > Line 804-810 of draft 0.16e, there is a resource match in Example
> 2
> > Rule
> > > 1:
> > > >
> > > > <ResourceMatch MatchId="function:node-match">
> > > > <ResourceAttributeDesignator AttributeId="urn:...:xpath"
> > > > DataType="xsi:string"/>
> > > > <AttributeValue
> DataType="xsi:string">/md:record</AttributeValue>
> > > > </ResourceMatch>
> > > >
> > > > In the above example, the node-match function is defined as
> > > >
> > > > Function: node-match
> > > > input: xs:string, xs:string
> > > > output: xs:boolean
> > > > description: receive two xpath expressions and executes xpath
> processor
> > > on
> > > > both xpaths. It generates two objects (object type is defined in
> XPath
> > > 1.0,
> > > > i.e. node-set, string, numeric, or boolean). When two objects have
> an
> > > > intersection, then it returns true, otherwise return false.
> > >
> > > This function, although a little unwieldy, is fine, provided you can
> > > provide a deterministic definition for a node-match. ("when two
> object
> > > have an intersection") is somewhat lacking.
> > >
> > > > Instead of the above node-match function and the resource match
> > > > specification, I would prefer the definition and resource match
> > > > specification using <AttributeSelectorIndirect> below:
> > > >
> > > > Function: node-match
> > > > input: object, object
> > > > output: xs:boolean
> > > > description: receive two objects. When two node-sets have an
> > > intersection,
> > > > then it returns true, otherwise return false.
> > > >
> > > > <ResourceMatch MatchId="function:node-match">
> > > > <AttributeSelectorIndirect>
> > > > <ResourceAttributeDesignator AttributeId="urn:...:xpath"/>
> > > > </AttributeSelectorIndirect>
> > > > <AttributeSelector RequestContextPath="/md:record"/>
> > > > </ResourceMatch>
> > >
> > > Why?
> > >
> > > Your previous approach is fine, and works within our type system. It
> > takes
> > > two arguments of primitive types ("xs:string") and returns an
> xs:boolean.
> > >
> > > This approach requires "node-match" to be polymorphic and for XACML
> > > processors to understand abstract data types. Our simple type system
> > > cannot support it. We would now have much more than primitive types,
> and
> > > sequences of primitive types. We would have abstract data types
> (i.e.
> > > arbitrary XML nodes) introduced into the type system.
> > >
> > > Also, in this case, you must note that the selectors must contain
> the
> > > "DataType" attribute to make type sense out of their results, as
> these
> > > selectors can end up in other function applications. I think we are
> > > trying to get rid of the DataType attribute, because of the type
> > > inference.
> > >
> > > Also, I think you left the "DataType" attribute out in this example,
> for
> > > obvious reasons. You don't know what legal value to give it.
> > >
> > > In both cases, however, you still need to come up with an explicit
> > > specification of for the function "node-match".
> > >
> > > If you can come up with a specification of node-match, I would
> strongly
> > > prefer that it was a function that fit with our type system, i.e.
> your
> > > first example, which takes two XPATH expressions and returns a
> boolean.
> > >
> > >
> > > > Other example (not AttributeSelectorIndirect but AttributeSelector
> > case)
> > > is
> > > > line 825-835. The function:string-equal should be the
> > > > function:general-string-equal because <AttributeSelector> returns
> an
> > > object
> > > > data type (maybe node-set) and it is not proper to hand it to
> > > string-equal
> > > > function.
> > >
> > > I don't even have a specification for "string-equal", let alone
> > > "general-string-equal", so I don't really understand the difference.
> > >
> > > Cheers,
> > > -Polar
> > >
> > > > <Condition FunctionId="function:string-equal">
> > > > <SubjectAttributeDesignatorWhere
> > > > AttributeId="urn:...:policy-number" DataType="xsi:string"/>
> > > > <AttributeSelector RequestContextPath="/ctx:Request/ ...
> > > > /md:policyNumber"
> > > > DataType="xsi:string"/>
> > > > </Condition>
> > > >
> > > > [should be]
> > > >
> > > > <Condition FunctionId="function:general-string-equal">
> > > > <SubjectAttributeDesignatorWhere
> > > > AttributeId="urn:...:policy-number" DataType="xsi:string"/>
> > > > <AttributeSelector RequestContextPath="/ctx:Request/ ...
> > > > /md:policyNumber"
> > > > DataType="xsi:string"/>
> > > > </Condition>
> > > >
> > > > Michiharu Kudo
> > > >
> > > > IBM Tokyo Research Laboratory, Internet Technology
> > > > Tel. +81 (46) 215-4642 Fax +81 (46) 273-7428
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > Polar Humenn
> > > > <polar@syr.edu> To: Michiharu
> > > Kudoh/Japan/IBM@IBMJP
> > > > cc:
> > > <xacml@lists.oasis-open.org>
> > > > 2002/08/30 03:27 Subject: Re:
> [xacml]
> > [CR]
> > > AttributeSelectorIndirect
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > Michiharu,
> > > >
> > > > Is there a use case or example for this type of attribute
> selector?
> > > >
> > > > Cheers,
> > > > -Polar
> > > >
> > > > On Thu, 29 Aug 2002, Michiharu Kudoh wrote:
> > > >
> > > > > Based on the discussion on Monday call, Simon and I agreed to
> > changing
> > > > the
> > > > > schema to support an AttributeSelectorIndirect element to
> retrieve
> a
> > > > XPath
> > > > > expression from the context. I wonder whether the name of this
> > element
> > > is
> > > > > appropriate or not.
> > > > >
> > > > > <xs:complexType name="AttributeSelectorBaseType">
> > > > > <xs:element ref="xacml:XPathNamespace" minOccurs="0" maxOccurs
> > > > > ="unbounded"/>
> > > > > <xs:attribute name="DataType" type="xs:anyURI"
> use="optional"/>
> > > > > <xs:attribute name="XPathVersion" type="xs:anyURI"
> use="optional"
> > > > default
> > > > > ="http://www.w3.org/TR/1999/Rec-xpath-19991116"/>
> > > > > </xs:complexType>
> > > > >
> > > > > <xs:complexType name="AttributeSelectorType">
> > > > > <xs:complexContent>
> > > > > <xs:extension base="AttributeSelectorBaseType">
> > > > > <xs:attribute name="RequestContextPath" type="xs:string"
> use
> > > > > ="required"/>
> > > > > </xs:extension>
> > > > > </xs:complexContent>
> > > > > </xs:complexType>
> > > > >
> > > > > <xs:complexType name="AttributeSelectorIndirectType">
> > > > > <xs:extension base="AttributeSelectorBaseType">
> > > > > <xs:choice>
> > > > > <xs:element ref="xacml:SubjectAttributeDesignator"/>
> > > > > <xs:element ref="xacml:ResourceAttributeDesignator"/>
> > > > > <xs:element ref="xacml:ActionAttributeDesignator"/>
> > > > > <xs:element ref="xacml:EnvironmentAttributeDesignator"/>
> > > > > </xs:choice>
> > > > > </xs:extension>
> > > > > </xs:complexType>
> > > > >
> > > > > <xs:element name="AttributeSelector"
> type="AttributeSelectorType"/>
> > > > > <xs:element name="AttributeSelectorIndirect" type
> > > > > ="AttributeSelectorIndirectType"/>
> > > > >
> > > > > <xs:element name="XPathNamespace"
> type="xacml:XPathNamespaceType"
> > > > > substitutionGroup="xacml:AbstractDefaults"/>
> > > > > <xs:complexType name="XPathNamespaceType">
> > > > > <xs:attribute name="NamespaceURI" type="xs:anyURI"/>
> > > > > <xs:attribute name="Prefix" type="xs:string" use="optional"/>
> > > > > </xs:complexType>
> > > > >
> > > > >
> > > > > Sample text for this element:
> > > > >
> > > > > 5.28. Element <AttributeSelectorIndirect>
> > > > >
> > > > > The <AttributeSelectorIndirect> element is a free-form pointing
> > device
> > > > into
> > > > > the <xacml-context:Request> element using an attribute
> designator.
> > The
> > > > > actual xpath expression is retrieved from the context pointed by
> that
> > > > > attribute designator. Other than that, the semantics is the same
> with
> > > > > <AttributeSelector> element. Support for the
> > > <AttributeSelectorIndirect>
> > > > > element is OPTIONAL.
> > > > >
> > > > > The <AttributeSelectorIndirect> element is of
> > > > AttributeSelectorIndirectType
> > > > > complex type.
> > > > > The <AttributeSelectorIndirect> element has either one of the
> > following
> > > > > elements:
> > > > >
> > > > > SubjectAttributeDesignator
> > > > > ResourceAttributeDesignator
> > > > > ActionAttributeDesignator
> > > > > EnvironmentAttributeDesignator
> > > > >
> > > > > Michiharu
> > > > >
> > > > > IBM Tokyo Research Laboratory, Internet Technology
> > > > > Tel. +81 (46) 215-4642 Fax +81 (46) 273-7428
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
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> > > >
> > > >
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