Re: [netmod] WG Last Call for draft-ietf-netmod-yang-metadata-02 (until 2015-10-22)

[Ladislav Lhotka]

Juergen Schoenwaelder  writes:

> On Thu, Oct 15, 2015 at 09:52:00AM +0200, Ladislav Lhotka wrote:
>
> [...]
>  
>> The "schema" part addresses syntactic changes in protocol messages,
>> which are inevitable, and the second part is about risky
>> annotations. I agree evil annotations should be banned but I am not
>> sure we can find a satisfactory formulation. Do you have any
>> suggestion?
>
> Perhaps the simples solution is to remove the first sentence in order
> to avoid having 'schema' understood in different ways. (I personally
> believe an annotation MUST NOT change data model semantics but lets
> try to find a compromise.) So my proposal is to replace the entire
> paragraph with:
>
>Due care has to be exercised when introducing annotations in network
>management systems in order to avoid interoperability problems and
>software failures.  The following aspects should be taken into
>account:

I am fine with this. In a parallel thread I proposed to extend YANG spec
with a general permission for instance data and protocol messages to
include annotations (in any encoding). This would help to make sure that
compliant parsers won't choke on XML attributes or JSON objects whose
names start with "@".

Would this be acceptable?

Lada

>
> /js
>
> -- 
> Juergen Schoenwaelder   Jacobs University Bremen gGmbH
> Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany
> Fax:   +49 421 200 3103 

-- 
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PGP Key ID: E74E8C0C

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Re: [netmod] WG Last Call for draft-ietf-netmod-yang-metadata-02 (until 2015-10-22)

[Juergen Schoenwaelder]

On Thu, Oct 15, 2015 at 09:52:00AM +0200, Ladislav Lhotka wrote:

[...]
 
> The "schema" part addresses syntactic changes in protocol messages,
> which are inevitable, and the second part is about risky
> annotations. I agree evil annotations should be banned but I am not
> sure we can find a satisfactory formulation. Do you have any
> suggestion?

Perhaps the simples solution is to remove the first sentence in order
to avoid having 'schema' understood in different ways. (I personally
believe an annotation MUST NOT change data model semantics but lets
try to find a compromise.) So my proposal is to replace the entire
paragraph with:

   Due care has to be exercised when introducing annotations in network
   management systems in order to avoid interoperability problems and
   software failures.  The following aspects should be taken into
   account:

/js

-- 
Juergen Schoenwaelder   Jacobs University Bremen gGmbH
Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany
Fax:   +49 421 200 3103 

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Re: [netmod] WG Last Call for draft-ietf-netmod-yang-metadata-02 (until 2015-10-22)

[Ladislav Lhotka]

> On 15 Oct 2015, at 09:03, Juergen Schoenwaelder 
>  wrote:
> 
> On Wed, Oct 14, 2015 at 04:01:13PM +0200, Ladislav Lhotka wrote:
>> Juergen Schoenwaelder  writes:
>> 
>>> On Tue, Oct 13, 2015 at 03:09:34PM +0200, Ladislav Lhotka wrote:
 
> On 13 Oct 2015, at 13:01, Juergen Schoenwaelder 
>  wrote:
> 
> On Wed, Oct 07, 2015 at 05:37:36PM +, Kent Watsen wrote:
>> 
>> This is a notice to start a NETMOD WG last call for the document:
>> 
>> Defining and Using Metadata with YANG
>> http://tools.ietf.org/html/draft-ietf-netmod-yang-metadata-02
>> 
>> Please indicate your support by Thursday October 22, 2015 at 9PM EDT.
>> We are not only interested in receiving defect reports, we are equally
>> interested in statements of the form:
>> 
> 
> I am concerned about this text:
> 
>  Annotations modify the schema of datastores and/or management
>  protocol messages, and may also change their semantics.  Therefore,
>  due care has to be exercised when introducing annotations in
>  network management systems in order to avoid interoperability
>  problems and software failures.
> 
> I think we should actually very clearly discourage annotations that
> modify the schema of datastores and/or management protocol messages
> instead of assuming all annotations are free to do so.
 
 Annotations modify the schemas by definition because otherwise XML 
 attributes, and objects in JSON encoding whose names start with "@", are 
 not allowed.
 
>>> 
>>> For me, the schema of a datastore is the YANG data model. I do not
>>> want annotations that change the YANG data model of a datastore.
>>> Perhaps you mean something different but then the text allows multiple
>>> interpretations and hence it is problematic.
>> 
>> It depends on the definition of "schema". In any case, annotations add
>> some extra information that possibly might be persistent. FWIW, a RELAX
>> NG schema generated for datastore + annotation is different from the one
>> that's for datastore only.
> 
> Then this usage of "schema" needs to be clarified. The text in
> question does not say it is specific to RELAX NG schema. It can be
> read as "annotations modify the YANG data models and/or
> NETCONF/RESTCONF protocol messages". I do not want to legalize
> annotations that turn data model properties upside down.

Annotations may not turn data model properties upside down but in any case they 
add stuff that the peer may not be prepared to handle. If the NETCONF client 
doesn't expect XML attributes in the data part of a  reply, then it 
might break if the server uses them. That's what I meant by "schema changes" 
and this problem is relevant for all uses of annotations, regardless of their 
semantics.

> 
>>> Annotations should add metadata but I think metadata must not change
>>> the semantics of the data model itself. I am also concerned if
>>> metadata changes the semantics of protocol messages. I am not
>> 
>> Some annotations that are of this sort, such as "inactive", have already
>> been discussed. The text you cited tries to explain possible pitfalls of
>> such annotations, but my understanding of the consensus so far has been
>> that it is not desirable to limit annotations to "benign" ones.
> 
> I am fine with the bullets, my concern is about the paragraph above
> it. For me, there are different classes of annotations
> 
> - easy annotations that only add metadata (like the 'last-modified'
>  example) and which are harmless (since they can be simply ignored)
> 
> - risky annotations that impact the interpretation of data (such as an
>  'inactive' annotation) and which require that systems agree that
>  they understand the semantics of the annotations before they can be
>  used safely
> 
> - evil annotations that are trying to overwrite essential data model
>  properties (e.g. a 'key' annotation that redefines the key property
>  of a list or a 'type' annotation that overwrites the type of leafs
>  or a 'config' annotation that redefines the config true/false
>  property on the fly)
> 
> Yes, the boundary between these classes is fuzzy. I am concerned that

Yes, and the boundary may also depend on the presence of external information 
such as protocol specification.

> a statement like
> 
>   Annotations modify the schema of datastores and/or management
>   protocol messages, and may also change their semantics.


The "schema" part addresses syntactic changes in protocol messages, which are 
inevitable, and the second part is about risky annotations. I agree evil 
annotations should be banned but I am not sure we can find a satisfactory 
formulation. Do you have any suggestion?

> 
> paves the way to encourage not only risky but also evil annotations.
> People might point to this statement and say that evil 

Re: [netmod] WG Last Call for draft-ietf-netmod-yang-metadata-02 (until 2015-10-22)

[Juergen Schoenwaelder]

On Wed, Oct 14, 2015 at 04:01:13PM +0200, Ladislav Lhotka wrote:
> Juergen Schoenwaelder  writes:
> 
> > On Tue, Oct 13, 2015 at 03:09:34PM +0200, Ladislav Lhotka wrote:
> >> 
> >> > On 13 Oct 2015, at 13:01, Juergen Schoenwaelder 
> >> >  wrote:
> >> > 
> >> > On Wed, Oct 07, 2015 at 05:37:36PM +, Kent Watsen wrote:
> >> >> 
> >> >> This is a notice to start a NETMOD WG last call for the document:
> >> >> 
> >> >> Defining and Using Metadata with YANG
> >> >> http://tools.ietf.org/html/draft-ietf-netmod-yang-metadata-02
> >> >> 
> >> >> Please indicate your support by Thursday October 22, 2015 at 9PM EDT.
> >> >> We are not only interested in receiving defect reports, we are equally
> >> >> interested in statements of the form:
> >> >> 
> >> > 
> >> > I am concerned about this text:
> >> > 
> >> >   Annotations modify the schema of datastores and/or management
> >> >   protocol messages, and may also change their semantics.  Therefore,
> >> >   due care has to be exercised when introducing annotations in
> >> >   network management systems in order to avoid interoperability
> >> >   problems and software failures.
> >> > 
> >> > I think we should actually very clearly discourage annotations that
> >> > modify the schema of datastores and/or management protocol messages
> >> > instead of assuming all annotations are free to do so.
> >> 
> >> Annotations modify the schemas by definition because otherwise XML 
> >> attributes, and objects in JSON encoding whose names start with "@", are 
> >> not allowed.
> >>
> >
> > For me, the schema of a datastore is the YANG data model. I do not
> > want annotations that change the YANG data model of a datastore.
> > Perhaps you mean something different but then the text allows multiple
> > interpretations and hence it is problematic.
> 
> It depends on the definition of "schema". In any case, annotations add
> some extra information that possibly might be persistent. FWIW, a RELAX
> NG schema generated for datastore + annotation is different from the one
> that's for datastore only.

Then this usage of "schema" needs to be clarified. The text in
question does not say it is specific to RELAX NG schema. It can be
read as "annotations modify the YANG data models and/or
NETCONF/RESTCONF protocol messages". I do not want to legalize
annotations that turn data model properties upside down.

> > Annotations should add metadata but I think metadata must not change
> > the semantics of the data model itself. I am also concerned if
> > metadata changes the semantics of protocol messages. I am not
> 
> Some annotations that are of this sort, such as "inactive", have already
> been discussed. The text you cited tries to explain possible pitfalls of
> such annotations, but my understanding of the consensus so far has been
> that it is not desirable to limit annotations to "benign" ones.

I am fine with the bullets, my concern is about the paragraph above
it. For me, there are different classes of annotations

- easy annotations that only add metadata (like the 'last-modified'
  example) and which are harmless (since they can be simply ignored)

- risky annotations that impact the interpretation of data (such as an
  'inactive' annotation) and which require that systems agree that
  they understand the semantics of the annotations before they can be
  used safely

- evil annotations that are trying to overwrite essential data model
  properties (e.g. a 'key' annotation that redefines the key property
  of a list or a 'type' annotation that overwrites the type of leafs
  or a 'config' annotation that redefines the config true/false
  property on the fly)

Yes, the boundary between these classes is fuzzy. I am concerned that
a statement like

   Annotations modify the schema of datastores and/or management
   protocol messages, and may also change their semantics.

paves the way to encourage not only risky but also evil annotations.
People might point to this statement and say that evil annotations
are just fine.

> I guess the considerations are similar to extensions in general:
> certain annotations may be a mandatory part of a protocol but is has
> to be said in the protocol spec. This is essentially what was done for
> NETCONF, and a special extension was used for defining the annotations
> (XML attributes).

NETCONF is a special case since NETCONF was designed before we had
YANG and the WG retrofitted a YANG data model to describe it.

/js

-- 
Juergen Schoenwaelder   Jacobs University Bremen gGmbH
Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany
Fax:   +49 421 200 3103 

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Re: [netmod] WG Last Call for draft-ietf-netmod-yang-metadata-02 (until 2015-10-22)

[Ladislav Lhotka]

Juergen Schoenwaelder  writes:

> On Tue, Oct 13, 2015 at 03:09:34PM +0200, Ladislav Lhotka wrote:
>> 
>> > On 13 Oct 2015, at 13:01, Juergen Schoenwaelder 
>> >  wrote:
>> > 
>> > On Wed, Oct 07, 2015 at 05:37:36PM +, Kent Watsen wrote:
>> >> 
>> >> This is a notice to start a NETMOD WG last call for the document:
>> >> 
>> >> Defining and Using Metadata with YANG
>> >> http://tools.ietf.org/html/draft-ietf-netmod-yang-metadata-02
>> >> 
>> >> Please indicate your support by Thursday October 22, 2015 at 9PM EDT.
>> >> We are not only interested in receiving defect reports, we are equally
>> >> interested in statements of the form:
>> >> 
>> > 
>> > I am concerned about this text:
>> > 
>> >   Annotations modify the schema of datastores and/or management
>> >   protocol messages, and may also change their semantics.  Therefore,
>> >   due care has to be exercised when introducing annotations in
>> >   network management systems in order to avoid interoperability
>> >   problems and software failures.
>> > 
>> > I think we should actually very clearly discourage annotations that
>> > modify the schema of datastores and/or management protocol messages
>> > instead of assuming all annotations are free to do so.
>> 
>> Annotations modify the schemas by definition because otherwise XML 
>> attributes, and objects in JSON encoding whose names start with "@", are not 
>> allowed.
>>
>
> For me, the schema of a datastore is the YANG data model. I do not
> want annotations that change the YANG data model of a datastore.
> Perhaps you mean something different but then the text allows multiple
> interpretations and hence it is problematic.

It depends on the definition of "schema". In any case, annotations add
some extra information that possibly might be persistent. FWIW, a RELAX
NG schema generated for datastore + annotation is different from the one
that's for datastore only.

>
> Annotations should add metadata but I think metadata must not change
> the semantics of the data model itself. I am also concerned if
> metadata changes the semantics of protocol messages. I am not

Some annotations that are of this sort, such as "inactive", have already
been discussed. The text you cited tries to explain possible pitfalls of
such annotations, but my understanding of the consensus so far has been
that it is not desirable to limit annotations to "benign" ones.

I guess the considerations are similar to extensions in general:
certain annotations may be a mandatory part of a protocol but is has
to be said in the protocol spec. This is essentially what was done for
NETCONF, and a special extension was used for defining the annotations
(XML attributes).

Lada

> interested in standards-track mechanisms that at the end increase the
> chances of interoperability problems and software failures.
>
> /js
>
> -- 
> Juergen Schoenwaelder   Jacobs University Bremen gGmbH
> Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany
> Fax:   +49 421 200 3103 

-- 
Ladislav Lhotka, CZ.NIC Labs
PGP Key ID: E74E8C0C

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Re: [netmod] WG Last Call for draft-ietf-netmod-yang-metadata-02 (until 2015-10-22)

[Juergen Schoenwaelder]

On Wed, Oct 07, 2015 at 05:37:36PM +, Kent Watsen wrote:
> 
> This is a notice to start a NETMOD WG last call for the document:
> 
> Defining and Using Metadata with YANG
> http://tools.ietf.org/html/draft-ietf-netmod-yang-metadata-02
> 
> Please indicate your support by Thursday October 22, 2015 at 9PM EDT.
> We are not only interested in receiving defect reports, we are equally
> interested in statements of the form:
>

I am concerned about this text:

   Annotations modify the schema of datastores and/or management
   protocol messages, and may also change their semantics.  Therefore,
   due care has to be exercised when introducing annotations in
   network management systems in order to avoid interoperability
   problems and software failures.

I think we should actually very clearly discourage annotations that
modify the schema of datastores and/or management protocol messages
instead of assuming all annotations are free to do so.

/js

-- 
Juergen Schoenwaelder   Jacobs University Bremen gGmbH
Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany
Fax:   +49 421 200 3103 

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Re: [netmod] WG Last Call for draft-ietf-netmod-yang-metadata-02 (until 2015-10-22)

[Robert Varga]

On 10/07/2015 07:37 PM, Kent Watsen wrote:


This is a notice to start a NETMOD WG last call for the document:

Defining and Using Metadata with YANG
http://tools.ietf.org/html/draft-ietf-netmod-yang-metadata-02



I have read the document, and coming in without the previous 
discussions, md:annotation instances feel like aspects (from 
aspect-oriented programming) being attached to pre-defined models to 
address a cross-cutting concern. Unfortunately it seems it lacks an 
equivalent of pointcut specification, e.g. a machine-readable definition 
where/when a particular annotation is valid.


This makes annotations disconnected from the YANG metamodel, which is 
not desirable for systems strictly based on the metamodel, as each 
instance of an annotation will require hand-written code.


My question is whether it would make sense to define some sort of 
(optional) pointcut specification to be carried within the md:annotation 
statement (such as an explicit list of data nodes, or a 'when' statement 
or similar)?


That would allow us to bind some/most md:annotation instances 
automagically to the metamodel, reducing the need to hand-code their 
semantics.


Thanks,
Robert
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Re: [netmod] WG Last Call for draft-ietf-netmod-yang-metadata-02 (until 2015-10-22)

[Ladislav Lhotka]

Hi Robert,

> On 13 Oct 2015, at 17:26, Robert Varga  wrote:
> 
> On 10/07/2015 07:37 PM, Kent Watsen wrote:
>> 
>> This is a notice to start a NETMOD WG last call for the document:
>> 
>> Defining and Using Metadata with YANG
>> http://tools.ietf.org/html/draft-ietf-netmod-yang-metadata-02
>> 
> 
> I have read the document, and coming in without the previous discussions, 
> md:annotation instances feel like aspects (from aspect-oriented programming) 
> being attached to pre-defined models to address a cross-cutting concern. 
> Unfortunately it seems it lacks an equivalent of pointcut specification, e.g. 
> a machine-readable definition where/when a particular annotation is valid.
> 
> This makes annotations disconnected from the YANG metamodel, which is not 
> desirable for systems strictly based on the metamodel, as each instance of an 
> annotation will require hand-written code.
> 
> My question is whether it would make sense to define some sort of (optional) 
> pointcut specification to be carried within the md:annotation statement (such 
> as an explicit list of data nodes, or a 'when' statement or similar)?

The easiest way would be to define "annotation" as a first-class data node. 
However:

- YANG was deliberately designed to avoid using XML attributes in the same way 
as XML schema languages,

- IMO this can't be done through an extension.

With must or when it would be difficult to determine the context node.

Lada

> 
> That would allow us to bind some/most md:annotation instances automagically 
> to the metamodel, reducing the need to hand-code their semantics.
> 
> Thanks,
> Robert
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Re: [netmod] WG Last Call for draft-ietf-netmod-yang-metadata-02 (until 2015-10-22)

[Juergen Schoenwaelder]

On Tue, Oct 13, 2015 at 03:09:34PM +0200, Ladislav Lhotka wrote:
> 
> > On 13 Oct 2015, at 13:01, Juergen Schoenwaelder 
> >  wrote:
> > 
> > On Wed, Oct 07, 2015 at 05:37:36PM +, Kent Watsen wrote:
> >> 
> >> This is a notice to start a NETMOD WG last call for the document:
> >> 
> >> Defining and Using Metadata with YANG
> >> http://tools.ietf.org/html/draft-ietf-netmod-yang-metadata-02
> >> 
> >> Please indicate your support by Thursday October 22, 2015 at 9PM EDT.
> >> We are not only interested in receiving defect reports, we are equally
> >> interested in statements of the form:
> >> 
> > 
> > I am concerned about this text:
> > 
> >   Annotations modify the schema of datastores and/or management
> >   protocol messages, and may also change their semantics.  Therefore,
> >   due care has to be exercised when introducing annotations in
> >   network management systems in order to avoid interoperability
> >   problems and software failures.
> > 
> > I think we should actually very clearly discourage annotations that
> > modify the schema of datastores and/or management protocol messages
> > instead of assuming all annotations are free to do so.
> 
> Annotations modify the schemas by definition because otherwise XML 
> attributes, and objects in JSON encoding whose names start with "@", are not 
> allowed.
>

For me, the schema of a datastore is the YANG data model. I do not
want annotations that change the YANG data model of a datastore.
Perhaps you mean something different but then the text allows multiple
interpretations and hence it is problematic.

Annotations should add metadata but I think metadata must not change
the semantics of the data model itself. I am also concerned if
metadata changes the semantics of protocol messages. I am not
interested in standards-track mechanisms that at the end increase the
chances of interoperability problems and software failures.

/js

-- 
Juergen Schoenwaelder   Jacobs University Bremen gGmbH
Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany
Fax:   +49 421 200 3103 

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[netmod] WG Last Call for draft-ietf-netmod-yang-metadata-02 (until 2015-10-22)

[Kent Watsen]

This is a notice to start a NETMOD WG last call for the document:

Defining and Using Metadata with YANG
http://tools.ietf.org/html/draft-ietf-netmod-yang-metadata-02

Please indicate your support by Thursday October 22, 2015 at 9PM EDT.
We are not only interested in receiving defect reports, we are equally
interested in statements of the form:

  * I have reviewed draft-ietf-netmod-yang-metadata-02 and I found no issues
  * I have implemented the data model in draft-ietf-netmod-yang-metadata-02
  * I am implementing the data model in draft-ietf-netmod-yang-metadata-02
  * I am considering to implement the data model in 
draft-ietf-netmod-yang-metadata-02

Of course, these are merely suggestions, folks can provide comments in any
form that suits them.

This is the second Last Call for this document, the first call being last June.

Kent  // as co-chair

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