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Subject: Re: [xacml] Updated policy template wiki


If that is the case, then the attribute designator approach will not work.

Best regards,

On 2012-10-11 05:44, Steven Legg wrote:


On 10/10/2012 6:25 PM, Erik Rissanen wrote:

Sorry, but it's still a bit unclear to me. Ok, I get it that if you have one template and N template
datasets, then you get N policies.

But why does that matter?

When a PEP calls to a PDP, the PDP is supposed to provide a single decision (not doing multi requests now) so this iteration does not need to happen. The PIP only needs to select the one dataset which applies to
this particular request.

In general, any number of those N policies may apply to a particular
request, not just one.


Best regards,

On 2012-10-10 08:58, Steven Legg wrote:


On 10/10/2012 4:57 PM, Erik Rissanen wrote:

Whatever information you are using to select the right template data when filling in the right template with the right data, could also be available to a PIP which would then know which attribute values to provide for any attribute designator. Or is there something I don't understand in the discussion?

The singular/plural ambiguity around "data" in policy template data is
bothersome, and not helpful to clarity, so I'm going to start saying
policy template data set (singular) and policy template data sets (plural).

In the case of a Policy Template Engine (PTE), the inputs are a policy template and any number of policy template data sets. The PTE just goes into a loop where it makes a copy of the policy template replacing the parameters in the template (in whatever syntax is used to represent them) with the corresponding parameter values in the current policy template data set it is considering in the current iteration of the loop. The PTE considers one, and only one, policy template data set in each iteration. The values of the parameters, either single values or bags, will typically be different on each iteration because they come from a different policy template data set. Each time around the loop the PTE spits out a policy template instance, which is a normal policy without parameters. If there are N policy template data sets, then there are N output policies. There is no explicit information that the PTE uses to decide which policy template data set to use.
The selection is inherent in the loop it performs.

Dynamic template reduction has to have the same effect as a PTE, which means that the PDP has to evaluate the policy template, which is now masquerading as a normal policy, as many times as there are policy template data sets known to the PIP (or alternatively, the context handler). Effectively, PIPs currently act as though there is only ever one policy template data set. Standard PIPs don't have the capability of storing multiple alternative sets of attributes. Nor is there a mechanism that a PDP could use to tell the PIP which set it wants right

Any clearer ?


Best regards,

On 2012-10-10 03:28, Steven Legg wrote:


On 10/10/2012 4:59 AM, Danny Thorpe wrote:


The equivalent of dynamic policy template reduction would require setting up a PIP with the PDP to provide the appropriate template-data values for a particular attribute ID when the PDP evaluates the <AttributeDesignator>. The PIP would need to be able to distinguish between your two template cases below (Curtiss, Packard vs Curtiss, Spad). If the PIP knew the context of which policy ID an
was being evaluated in, the PIP could make the decision of whether to return (Curtiss, Packard) or
Spad) to provide the semantics of the original policy template concept. Knowledge of the PDP evaluation state by PIPs is not part of the XACML spec, but could be provided by an implementation.

I could imagine manipulating the policy ID to indicate what substitution group(s) the policy belongs to. Policy template (ID = “ABC”) + parameter data set 1 => policy ID=”ABC/1”. Policy template (ID = “ABC”) + parameter data set 2 => policy ID=”ABC/2”. The policy bodies are identical, but their IDs differ.

A more generalized solution would be to tie the parameter substitution group selection to some artifact of the request (subject, resource) or the environment (PDP host organization). PIP returns parameter data
set 1
for the target attribute ID if the request context also contains a “green apple” attribute, else the PIP returns parameter data set 2. PIP returns parameter data set 1 if the organization’s country is X,
parameter data set 2 if the organization’s country is Y, etc.

But the PIP only needs to be that smart if the PDP is multi-tenant. In the use case of a shared policy (template) needing to be customized to a particular organization’s specific details (parameter data),
if the
PDP is dedicated to that one organization, the PIP could simply be loading the specific details (parameter data) from a config file. No need for decision branches in the PIP at all.

You only seem to be considering one possibility of use case 2 of the Policy Template Profile. I read use case 2 as allowing that the customization for a particular organization (i.e., the organization making use of the policy template, not the organizations that might be mentioned in the parameter data) could involve many policy template data. Those policy template data may overlap with the policy template data of another organization using the same template, or be completely different from the policy template data used by another organization using the same template. Use case 1 also calls for many policy template data in use at the same organization. I seem to recall it being written somewhere that the policy template data may number in the

For dynamic template reduction where there are multiple policy template data, we can't rely on information in the request to cause the PIP to select one parameter group. The PDP has to repeatedly evaluate the policy template causing (somehow) the PIP to return a different parameter group each time, each parameter group corresponding to a different policy template data, and this must occur during the evaluation of a single authorization request.



*Danny Thorpe *

Authorization Architect

*Dell*| Identity & Access Management, Quest Software

Quest Software is now part of Dell.

*From:*Jean-Paul Buu-Sao [mailto:jean-paul.buu-sao@tscp.org]
*Sent:* Tuesday, October 09, 2012 1:40 AM
*To:* Erik Rissanen; Steven Legg
*Cc:* Danny Thorpe; xacml@lists.oasis-open.org
*Subject:* RE: [xacml] Updated policy template wiki

For sake of clarity I would like to rephrase the thought process.

Here is the excerpt of a policy (TAA-1.1), expressing that the subject attribute "http://schemas.tscp.org/2012-03/claims/OrganizationID"; must be in the bag {"Curtiss", "Packard"}

<Condition FunctionId="urn:oasis:names:tc:xacml:1.0:function:and">

       <Apply xsi:type="AtLeastMemberOf"

<Apply functionId="urn:oasis:names:tc:xacml:1.0:function:string-bag">

<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string";>Curtiss</AttributeValue>

<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string";>Packard</AttributeValue>


<AttributeDesignator AttributeId="http://schemas.tscp.org/2012-03/claims/OrganizationID";
DataType="http://www.w3.org/2001/XMLSchema#string"; />




Here is the excerpt of a policy (TAA-1.2), expressing that the subject attribute "http://schemas.tscp.org/2012-03/claims/OrganizationID"; must be in the bag {"Curtiss", "Spad"}

<Condition FunctionId="urn:oasis:names:tc:xacml:1.0:function:and">

       <Apply xsi:type="AtLeastMemberOf"

<Apply functionId="urn:oasis:names:tc:xacml:1.0:function:string-bag">

<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string";>Curtiss</AttributeValue>

<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string";>Spad</AttributeValue>


<AttributeDesignator AttributeId="http://schemas.tscp.org/2012-03/claims/OrganizationID";
DataType="http://www.w3.org/2001/XMLSchema#string"; />




The two policies (TAA-1.1 and TAA-1.2) are similar, with the exception of the hard-coded values of the string bags used by the AtLeastMemberOf function. The idea is to have only one policy that does not
these hard-coded values. Instead we have a construct that would substitute the appropriate values. In the example above: {“Curtiss”, “Packard”} for TAA-1.1, {“Curtiss”, “Spad”} for TAA-1.2.

My initial proposal was to using the element <AttributeValue> without qualifying its contents values,
but by
specifying a ParameterId attribute, that would allow to substitute the appropriate values:

<Condition FunctionId="urn:oasis:names:tc:xacml:1.0:function:and">

       <Apply xsi:type="AtLeastMemberOf"

<Apply functionId="urn:oasis:names:tc:xacml:1.0:function:string-bag">

<AttributeValue ParameterId="organizations" DataType=http://www.w3.org/2001/XMLSchema#string/>


<AttributeDesignator AttributeId="http://schemas.tscp.org/2012-03/claims/OrganizationID";
DataType="http://www.w3.org/2001/XMLSchema#string"; />




I understand that instead, and in order to achieving the same effect, Erik’s proposal is to replace the <AttributeValue ParameterId=…> construct with the more standard <AttributeDesignator> construct, given
something like:

<Condition FunctionId="urn:oasis:names:tc:xacml:1.0:function:and">

       <Apply xsi:type="AtLeastMemberOf"

<Apply functionId="urn:oasis:names:tc:xacml:1.0:function:string-bag">

<AttributeDesignator CategoryId="urn:oasis:names:tc:xacml:1.0:policy:" AttributeId="organizations"
DataType="http://www.w3.org/2001/XMLSchema#string"; />


<AttributeDesignator AttributeId="http://schemas.tscp.org/2012-03/claims/OrganizationID";
DataType="http://www.w3.org/2001/XMLSchema#string"; />




If my interpretation is correct (at least on the intent, not on exact syntax; Erik, I apologize if I
missed your point), then some questions arise:

A.1) How would the authorization engine know where to go and fetch the desired values (i.e. from the
template-data or the TAA-1.2 template-data)?

A.2) The <AttributeDesignator> construct was, so far, meant to retrieve attributes values from (Subject, Resource, Environment) attributes. Are we introducing the possibility for the same construct to also retrieve attribute values from (policy-template) attributes? If so we need to make it explicit on the
specification, I would think.

B) Can the two use-cases called out at the beginning of
[https://wiki.oasis-open.org/xacml/Policy%20Template%20Profile] be supported by <AttributeDesignator>?

I assumed that use-case 1 requires a static reduction, that happens far before any actual authorization decision; hence <AttributeDesignator> cannot be used for the purpose of parameterization. If my assumption is correct, then we need a different mechanism to support use-case 1, which is damageable. My proposal was
to find a single syntax that would equally support both use-cases.



-----Original Message-----
From: Erik Rissanen [mailto:erik@axiomatics.com]
Sent: Tuesday, October 09, 2012 08:32
To: Steven Legg
Cc: Jean-Paul Buu-Sao; Danny Thorpe; xacml@lists.oasis-open.org <mailto:xacml@lists.oasis-open.org>
Subject: Re: [xacml] Updated policy template wiki


I am arguing against the whole concept of a template, thus there is no Policy Template Engine in my

What I am trying to say is that instead of adding a Policy Template Engine to the PDP before the policy is evaluated by the XACML engine, you can just use a regular XACML policy in the XACML engine.

You can solve the same use case this way. Say that you want a template which has a parameter called "foo" and then a Policy Template Engine which substitutes "foo" with values before the XACML engine. Instead you can have a regular XACML policy with attribute designator "foo" and a PIP which provides the value which
would have been provided by the policy template engine.

Best regards,


On 2012-10-09 02:46, Steven Legg wrote:


Sorry, I read too much into what you were saying. Please disregard my

previous response.

On 8/10/2012 5:38 PM, Erik Rissanen wrote:


Yes, just replace all parameters with attribute designators.

An issue with using attribute designators as parameters is that there

is ambiguity for the Policy Template Engine to resolve. Some attribute

designators in the policy template are "real" and are preserved as is,

and the other attribute designators are actually parameters that need

to be replaced by a bag of attribute values from the policy template


Your example only has one parameter as a designator and that

designator uses the same URI for the Category and AttributeId. Were

you intending that equivalence as a way of distinguishing an attribute

designator that is actually a parameter, or is it just because you had

to put something in the Category ? A Policy Template Engine could

always look in the policy template data to work out which designators

are really parameters, but I think it would be better if it were clear

from the designator. I suggest using a special category URI just for


The attribute designators that are actually parameters should always

use MustBePresent="true" so that an implementation that blindly

evaluates a policy template as a normal policy will appropriately

return an indeterminate decision.

It seems we have three proposals for representating parameters in



(1) Just use attribute designators. This means that targets can't have

parameters, but on-permit-apply-second can be used to get the same


Policy template data writers can determine whether a parameter is

single-valued or multi-valued by seeing whether the corresponding

attribute designator is wrapped in type-one-and-only.

(2) <ValueParameter> and <BagParameter> elements. Targets can have

value parameters, but not bag parameters, though

on-permit-apply-second can be used to get the same effect. It's

obvious to policy template data writers what the parameters are and

whether a parameter is single-valued or multi-valued.

(3) ParameterId XML attribute on <AttributeValue> elements. It's

reasonably obvious to policy template data writers what the parameters

are. An additional XML attribute to indicate whether the parameter is

single-valued or multi-valued would make this solution cleaner.

Targets can have value parameters. Targets could also have bag

parameters provided the target is transformed by the Policy Template

Engine. Alternatively, bag parameters in targets could be disallowed

because on-permit-apply-second can be used to get the same effect.

I don't see a compelling need for transformations of conditions.


(1) and (2) don't lend themselves to transformations, but it could be


The difference in the proposals is mostly around the syntax for

representing parameters.



I don't understand why you need to evaluate the template twice. I

tried to understand it from the wiki, but to me it all looks like

simple value substitution, which can handled better with attribute


Best regards,


On 2012-10-08 04:32, Steven Legg wrote:


On 5/10/2012 6:03 PM, Erik Rissanen wrote:


I put in one such example on the wiki page. Search for

"on-permit-apply-second" and you will find it.

This strategy only works if there is one policy template data for

the policy template. In general, there may be many policy template

data per policy template. The example in the wiki has two: TAA-1.1 and TAA-1.2.

Although you didn't do it, I assume you meant to replace the

parameters in the condition with attribute designators as well,

i.e., designators for "organizations", "nationals" and "workEfforts".

The policy needs to be evaluated twice. The first time the attribute

designator for PolicyIdOnResource needs to return

"urn:curtiss:ba:taa:taa-1.1", the designator for "organizations"

needs to return the bag of { "Curtiss", "Packard" }, the designator

for "nationals" needs to return the bag of { "US", "GB" }, and

"workEfforts" needs to return { "DetailedDesign", "Simulation" }.

The second time, PolicyIdOnResource needs to return

"urn:curtiss:ba:taa:taa-1.2", "organizations" needs to return {

"Curtiss", "Spad" }, "nationals" needs to return { "US", "FR" } and


needs to return { "Integration", "Simulation" }.

Of course, we don't currently have a way to cause a policy to be

evaluated multiple times with the attribute designators returning

different bags each time. For one thing, the result of an attribute

designator is fixed for the entire duration of the processing of an

authorization request. The expansion of the policy template into a

policy template instance for each policy template data achieves the

same end.

The use of on-permit-apply-second is a good idea for removing the

need for any special processing of parameters in targets.



Best regards,


On 2012-10-04 23:01, Jean-Paul Buu-Sao wrote:


Apologies for missing the call today, as I was in a TSCP event,

together with Gerry and David of Axiomatics.

I have been much interested in the last findings, and agree that

if the “template” property that we are (all, I think) looking for

could be achieved with standard the <AttributeDesignator>

construct, rather than introducing new concepts, then this would

be for the better.

May I suggest that, in order to verify this assertion (so to

speak), some folks, such as Erik or Danny, would be kind enough to

propose an alternate proposal to the sample found on our Wiki


By the way, as a word of

caution, please disregard the in-correctness of the XCAML 3.0 of

section 1. of the example (yes the devil is in the details, and

David shown me how this example could be made compliant).

Thanks in advance,



[mailto:xacml@lists.oasis-open.org] <mailto:[mailto:xacml@lists.oasis-open.org]> *On Behalf Of
*Danny Thorpe

*Sent:* Thursday, October 04, 2012 20:11

*To:* Erik Rissanen; xacml@lists.oasis-open.org <mailto:xacml@lists.oasis-open.org>

*Subject:* RE: [xacml] Updated policy template wiki

When the original proposal for policy templates was brought

forward, I noted that simply replacing a single AttributeValue

element with a list of values from the policy template <Parameter>

would fail in <Match> expressions, since <Match> is very explicit

about one value, one designator/selector. I offered a transform

to help produce valid match expressions.

AttributeDesignator does provide similar

“insert-multiple-values-here” operations to the policy template

substitution behavior, but I believe the suggestion of policy

parameterization came up because of situations in which

AttributeDesignator cannot be used. Comparing an  attribute

against a static list of test values (specific to an organization

or location and applied to a generic policy), for example, is a

many-to-many comparison, but cannot be expressed in a <Match>


As we discussed on the TC call today, we’re finding more

difficulties with parameter substitution the deeper we dig. Steven

Legg noted in an earlier email that some Xacml functions that take

single <AttributeValue> won’t work if multiple values are dropped

in to replace the <AttributeValue>. This means some sort of

expression transform will be necessary in condition expressions as

well to move policy templates forward.

In light of these increasing complexities and challenges, I’m

beginning to agree with you that perhaps the policy template use

case can better be addressed using the existing


This would mean:

1.Giving up parameterization behavior in <Match> expressions and

moving that logic into conditions using <AttributeDesignator> to

reference an attribute ID representing the parameterization data.

2.Moving parameterization data from a static policy generator step

to a PIP to fill <AttributeDesignator> references to a particular

attribute ID with parameterization data in the PDP at auth request

evaluation time.

Using <AttributeDesignator> instead of policy templates does

impact the use case quite a bit because populating PIP data is not

part of the Xacml spec. Policies could be shared between

organizations per the use case, but how the parameterization data

is applied to those policies would become a vendor-specific

implementation detail.

I can see the attraction of parameterizing policies to allow

up-front synthesis of specific policies, but as we say “the devil

is in the details.” The details are winning. :/


*Danny Thorpe *

Authorization Architect

Dell | Identity & Access Management, Quest Software

Quest Software is not part of Dell.



[mailto:xacml@lists.oasis-open.org] <mailto:[mailto:xacml@lists.oasis-open.org]>

<mailto:[mailto:xacml@lists.oasis-open.org]> *On Behalf Of *Erik


*Sent:* Thursday, October 04, 2012 4:42 AM

*To:* xacml@lists.oasis-open.org <mailto:xacml@lists.oasis-open.org>


*Subject:* Re: [xacml] Updated policy template wiki


I still fail to see why this is useful.

If you take a policy template, and replace each <Parameter> with

an appropriate <AttributeDesignator>, then you get a regular XACML

policy, and the PEP/PDP can "fill in"

the "template" at runtime using normal XACML attributes.

Why do we need a new standard? In particular I would be opposed to

"implementation option C", that is a PDP would construct the

policy from the template at runtime.

That's lots of heavy machinery for no gain.

Best regards,


On 2012-09-20 20:25, Danny Thorpe wrote:

    I’ve updated the policy template wiki


    with text about required Match expression rewriting in

parameter substitution and optional use of

AttributeDesignators and AttributeSelectors in Parameter data

in dynamic policy template reduction



    *Danny Thorpe *

    Product Architect | | *Quest Software*- /Now including the

people and products of BiTKOO/ |

www.quest.com <http://www.quest.com> <http://www.quest.com>

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