Appended is an updated summary of #72a-d, and #73a-j. Anne -- Anne H. Anderson Email:
Anne.Anderson@Sun.COM Sun Microsystems Laboratories 1 Network Drive,UBUR02-311 Tel: 781/442-0928 Burlington, MA 01803-0902 USA Fax: 781/442-1692 0072.
http://lists.oasis-open.org/archives/xacml-comment/200212/msg00039.html Subject: 5.31 Element <AttributeSelector> From: John Merrells <
merrells@jiffysoftware.com> Date: Thu, 05 Dec 2002 12:16:38 -0800 ------------------------------------------------------------------------ 0072a. If you want to enforce type correctness between the selector and the values then you have these choices... 1) The author of the XPath expression must write the expression so that it matches both the AttributeId and the DataType. Subject/Attribute[AttributeId= '...subject-id' and DataType"..."]/AttributeValue or, 2) the processor must enforce the type correctness. Option 1 is clearly error prone as people just won't bother, option 2 could be quite hard. [Although using the AttributeValue as the context node you could say "../@DataType"] CATEGORY: Incomplete. STATUS: Not yet discussed. RESPONSE: ACTIONS: DISCUSSION: [Anne Anderson] I think we specified option 2 in the resolution to 0052b: The XACML context handler must filter the values returned by the XPath expression based on matching the DataType, returning only those that match the DataType to the PDP. [John Merrells, responding to Michiharu Kudo] >For the type correctness, I don't expect that option 1 always >occurs. So each implementation should enforce the type >correctness. I mean that the processor just calls some XPath >processor to retrieve the requested node set irrespective of the >datatype specified in the selector. After some string >conversions are performed, the processor checks whether each >string value can be converted to the datatype specified in the >selector. Either way, this kind of run-time type checking should >be implemented for the case of ResourceContent. Good. The specification text needs to be changed. Currently it states: "In the case where the XPath expression matches attributes in the request context by AttributeId, it must also match the attribute's data-type with the selector's DataType. " >If XPath expression does not include a predicate expression to >satisfy data type requirement (Subject/Attribute[AttributeId= >'...subject-id' and DataType"..."]/AttributeValue), it can >select a node that has different data type. But I think this is >the problem of the policy specification and not the problem of >the AttributeSelector specification. Certainly, it would be >better to add some note about this in the specification. Yes. If the expression author writes an XPath that selects multiple attribute values with different DataTypes, then that is their problem. It would be good for the specification to point this out for expression writers. -------------------------------------------------------------------------- 0072b. How is the selected node converted into a value? You can convert a node into a string-value, as defined in the XPath spec. You then have a choice of using the string to value conversions that are defined in XPath, or use the conversions as defined in XACML. I would specify as the later, as XPath has some oddities in this area. (ie. The string 'false' has the boolen value true.) CATEGORY: Incomplete. STATUS: Not yet discussed. RESPONSE: ACTIONS: DISCUSSION: [Anne Anderson] I believe this is clearly specified in Section 5.33, pdf:2404-2415: XPath 1.0: apply "string" function XPath 2.0: use xf:string accessor function. [John Merrells, responding to Michiharu Kudo] >I think that the semantics of the AttributeSelector should >conform to the specified version of the XPath. So the conversion >functions would be ones specified in the corresponding XPath >specification. In the case of XPath 1.0, each conversion (node >set to string value and string value to each data type) would be >the conversion specified in XPath 1.0 even if it may have some >oddities in it. I'd suggest that Implementors of XACML will find it easier to convert a string into an XACML type, than to convert a string into an XPath type and then into an XACML type. Fisrtly the XPath conversion functions would have to be exposed through the XPath processor API. The XPath interface specification does not mandate this. Also, the string to XACML type constructors should be readily available. [As the implementor will almost certainly have implemented these for expression processing.] Secondly, the specification will have to provide a table that maps the XPath type system onto the XACML type system. -------------------------------------------------------------------------- 0072c. The next problem is working out which type to convert the string-value into. If we assume that the author or processor has checked that the selector and value types match then we can use the DataType specified in the selector. CATEGORY: Incomplete. STATUS: Not yet discussed. RESPONSE: ACTIONS: DISCUSSION: [Anne Anderson] I believe this is specified in the response to #52b: The XACML context handler must filter the values returned by the XPath expression based on matching the DataType, returning only those that match the DataType to the PDP. [John Merrells, responding to Michiharu Kudo] >And I could not find any XACML function definition that converts >"false" string value to False boolean value in the committee >specification. Which function are you talking about? Section '4.3 Boolean Functions': "Function: boolean boolean(object) ... a string is true if and only if its length is non-zero" >If the conversion failed, then "Indeterminate" should be >returned (optionally with some status code such as >syntax-error). This statement should be added to the specification. -------------------------------------------------------------------------- 0072d. Another example that should be explored is an XPath expression executed over the ResourceContent. In this case there are no DataTypes provided with the values, so there's no type checking that can be performed. We can only assume that the value provided is a valid representation for a an instance of the value of DataType specified in the selector. If the value can not be coerced into that DataType then what should the processor return? CATEGORY: Incomplete. STATUS: Not yet discussed. RESPONSE: ACTIONS: DISCUSSION: [Michiharu Kudo] In the case of ResourceContent, the selected node set and resultant string value(s) must be checked against the data type specified in the selector. If the conversion failed, then "Indeterminate" should be returned (optionally with some status code such as syntax-error). =========================================================================== 0073.
http://lists.oasis-open.org/archives/xacml-comment/200212/msg00047.html Subject: XACML 1.0 Committee Specification Comments From: "Chopra, Dipak" <
dipak.chopra@sap.com> Date: Mon, 09 Dec 2002 05:44:55 +0100 I reviewed the XACML 1.0 Committee Spec and here is the list of questions/comments. ---------------------------------------------------------------------------------- 0073a. Can PAP and PDP exchange Policy Set? Based on the Section 3.1 Data Flow Model, it seems like only Policy can be exchanged. If that is the case, how can PDP evaluate Policy Set as mentioned in Section 7.7 Policy Set Evaluation? CATEGORY: Unclear. STATUS: Not yet discussed. RESPONSE: ACTIONS: DISCUSSION: ---------------------------------------------------------------------------------- 0073b. What is the commonality between different Policy elements in the same Policy Set? The requirement on line #354 seems to indicate that the merging of different Policy elements into Policy Set is governed by "a given action". Does it mean that the cardinality between Policy Set and Action is 1 to 1? It seems confusing as schema does not suggest that. CATEGORY: Unclear. STATUS: Not yet discussed. RESPONSE: ACTIONS: DISCUSSION: ---------------------------------------------------------------------------------- 0073c. As Target can have multiple Resource and Action elements, not every Action is valid for each Resource. But the current schema allows to provide more non-existent access to resources. CATEGORY: Unclear. STATUS: Not yet discussed. RESPONSE: ACTIONS: DISCUSSION: ---------------------------------------------------------------------------------- 0073d. What is the significance of an Obligation with FulfillOn="Deny"? Which use case needs this feature? CATEGORY: Unclear. STATUS: Not yet discussed. RESPONSE: ACTIONS: DISCUSSION: ---------------------------------------------------------------------------------- 0073e. Line #2675, scope can be "Descendants" or "Children" as mentioned on lines #2907, 2908 in the case of multiple results. CATEGORY: Unclear. STATUS: Not yet discussed. RESPONSE: ACTIONS: DISCUSSION: ---------------------------------------------------------------------------------- 0073f. Section 7.6 Policy Evaluation. The table should be Policy truth table. CATEGORY: Unclear. STATUS: Not yet discussed. RESPONSE: ACTIONS: DISCUSSION: ---------------------------------------------------------------------------------- 0073g. Section 7.7 Policy Set Evaluation. The table should be Policy Set truth table. CATEGORY: Unclear. STATUS: Not yet discussed. RESPONSE: ACTIONS: DISCUSSION: ---------------------------------------------------------------------------------- 0073h. In this table, what is the meaning of "Effect" of Policy. As far as schema is concerned, Policy does not have this attribute. Only Rule has Effect element. Probably the right statement "At least one policy value has the calculated effect value". CATEGORY: Unclear. STATUS: Not yet discussed. RESPONSE: ACTIONS: DISCUSSION: ---------------------------------------------------------------------------------- 0073i. Line #2907, 2908. It seems like authorization decision MAY include multiple results based on the structure of resource sub-tree. I think this mechanism provides more information than requested. PEP is requesting if this subject(s) has the specified access (actions(s)) on the specified resource and its child nodes. The response should be one result. Why would PEP want to get detailed result information for each sub-node under resource? PEP must know about the structure (if there is any) of the requested resource and accordingly request for authorization decision from PDP. Based on that response, PEP should be able to allow or disallow the request. On line #2968, it says only one Decision element, which is not right based on lines #2907, 2908. CATEGORY: Unclear. STATUS: Not yet discussed. RESPONSE: ACTIONS: DISCUSSION: ---------------------------------------------------------------------------------- 0073j. There are two different types of resources. Functionality resource and data-instance resource. For example, ManagePO resource can be used to create/delete/modify an instance of PO. So ManagePO is a type of functionality type resource and instance of PO is a data-instance type resource. If we need to mandate that this action of this data-instance type resource can only be permitted by this functionality-type resource, how do we enforce that? CATEGORY: Unclear. STATUS: Not yet discussed. RESPONSE: ACTIONS: DISCUSSION: =====================================================================================