Re: [apps-discuss] apps-team review of draft-ietf-xcon-ccmp-13
ht@inf.ed.ac.uk (Henry S. Thompson) Wed, 01 June 2011 10:45 UTC
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To: Mary Barnes <mary.ietf.barnes@gmail.com>
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From: ht@inf.ed.ac.uk
Date: Wed, 01 Jun 2011 11:44:23 +0100
In-Reply-To: <BANLkTinpLY8FFoUBPCXz8+3k4uos+ftTeg@mail.gmail.com> (Mary Barnes's message of "Mon, 23 May 2011 13:59:25 -0500")
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Cc: Alan Johnston <alan.b.johnston@gmail.com>, apps-discuss@ietf.org, Richard Barnes <rbarnes@bbn.com>, Simon Pietro Romano <spromano@unina.it>, Chris Boulton <chris@ns-technologies.com>, xcon@ietf.org, iesg@ietf.org, Henning Schulzrinne <hgs+xcon@cs.columbia.edu>
Subject: Re: [apps-discuss] apps-team review of draft-ietf-xcon-ccmp-13
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Mary Barnes writes: > Thank you for your detailed review. Responses are inline below [MB]. > > On Mon, May 16, 2011 at 4:04 AM, Henry S. Thompson <ht@inf.ed.ac.uk>wrote: > >> I have been selected as the Applications Area Review Team reviewer for >> this draft (for background on apps-review, please see >> http://www.apps.ietf.org/content/applications-area-review-team). >> >> Please resolve these comments along with any other Last Call comments >> you may receive. Please wait for direction from your document shepherd >> or AD before posting a new version of the draft. >> >> Document: draft-ietf-xcon-ccmp-13 >> >> Title: Centralized Conferencing Manipulation Protocol >> >> Reviewer: Henry S. Thompson >> >> Review Date: 2011-05-13 >> >> Summary: This draft is almost ready for publication as a Proposed >> Standard but has a few issues that should be fixed before publication >> >> Major Issues: >> >> 4.2 Data Management >> >> 1) The approach to detecting competing updates and their consequences >> specified here seems unnecessarily complex. Was the alternative of >> including version numbers in _update_ messages (so that the server >> could reject any update whose target version had been superseded) >> considered and rejected? If so, perhaps a brief explanation of why >> it was rejected might be helful at this point. >> > [MB] The alternative was considered, however, with the XCON model, the > server is the only entity that "centralizes" information (in this case, the > available conference objects). A client might not have the very last version > of a conference object, due to the potential for concurrent operations > amongst independent client participants. However, an operation can still > succeed if there is no overlap amongst the data that is manipulated. Thus, > the server-side mechanism is what guarantees coherence in the data stored. > We can add some more text around that. Perhaps, prefacing the paragraph > with a statement about the model. [/MB] That sounds like a helpful addition. >> 2) In a related point, the statement at the end of this section that >> "a client subscribed to . . . notifications . . . will always have >> the most up-to-date version" is clearly false, in-so-far as it >> implies that such a client is guaranteed success for any update, as >> there is clearly a race condition here. >> > [MB] Yes, I can see that it's really not properly stated. The statement is > intending to say that the client will "get" the most up-to-date version with > the next notification - i.e., there is a way to recover in the case that the > update was either on an earlier version or no response received. [/MB] Right, something to that effect. . . >> 4.3 Data Model Compliance >> >> 1) Again this approach seems unnecessarily complex -- why does the >> data model have to constrain the initiation of a conference in this >> way. why not simply have messages which request new conference or >> new user IDs? >> > [MB] We do have messages for a new conference and new user IDs. The intent > here, was to eliminate the step of requesting those and thus have multiple > operations as a result of one request. We can add text around that. [/MB] Seems like a false economy to me, but yes, at least add a note. >> 2) I'm also confused by the fact that _elements_ described here as >> "mandatory" are not required by the schema. Specifically in 5.1 we >> will see that the 'confUserID' and 'confObjID' elements, which >> correspond precisely to XCON-USERID and XCON-URI which are >> described here as mandatory, appear in message type definitions as >> minOccurs="0", i.e. as optional. If they are optional, why is the >> above gensym complexity needed? If they are not optional, why >> doesn't the schema say so? >> > [MB] This is a common practice from what I have seen. This is because the > base request type is being reused, thus the elements are not mandatory for > each operation that uses the request type. So, the expectation is that it's > mandatory for the protocol for specific operations, but not mandatory in the > schema for all operations. In that case, XML Schema provides ways for the derived types to make inherited optional fields mandatory. . . > There may also be confusion in that the mandatory elements being referenced > are those in the *body* of the CCMP messages (the elements as defined in the > data model document) as opposed to the IDs in the *header* of the CCMP > messages defined in this document (confUserID and confObjID). > Perhaps this clarification would help? > OLD: > Since the XML documents carried in the CCMP need to be compliant with the > XCON data model... > NEW: > Since the XML documents carried in the body of CCMP requests/responses > need to be compliant with the XCON data model..." Yes. . . >> >> 3) It is unusual to refer to aspects of a data model with words such >> as 'element' and 'attribute', which are better reserved for use >> with respect to _XML serializations_ of data model instances. Ah, >> I see by looking at draft-ietf-xcon-common-data-model that the XCON >> data model is defined as an XML document. It's undoubtedly too >> late to do anything about that, but confounding data models and XML >> serializations is usually considered to be a mistake. . . >> > [MB] Can you characterize in what sense it is a mistake and what problems > it might cause? Or is it purely a nomenclature issue that is inaccurate? > I agree that resolving this concern would impact the data model. [/MB] Data is not inherently tree-structured. Thinking about data models as if they were often leads to awkward-at-best compromises. But in the end this was just a comment to explain to myself why what I think of as XML (serialisation) terminology was being applied to the data model. It might be worth including a note early on explaining that the data model is specified _as_ an XML infoset. . . >> 12.5 CCMP Protocol Registry >> >> Why are these registries needed? No role is specified for them >> anywhere in the body of the document. Registries are not free, and if >> all the information in the registry is also in the published schemas >> it's not at all clear what purpose they will serve. >> > [MB] We define the registries as the protocol is extensible and does > require specification. The registries also allow a reference to the > appropriate document that defines the normative behavior for the new > operations and new error codes. This is a standard procedure for RAI area > protocols - c.f., HELD (RFC 5985), SIP (RFC 3261), Registry for SIP header > field parameters (RFC 3698)... > I will note that we don't typically add a reference in the document that we > are defining the IANA registries. Is there a particular place you suggest > we add such a reference? Same place you end up putting the URIs for the XML Schema documents, maybe? > >> Minor Issues: >> >> >> 6.2. Alice gets detailed information about a specific blueprint >> >> The blueprintResponse message is not schema-valid per ccmp.xsd. On >> lines 32 and 33 of the example read >> <xcon:floor-request-handling>confirm >> </xcon:floor-request-handling> >> The problem really lies in DataModel.xsd -- whereas (correctly) >> ccmp.xsd uses xs:token as the base type for enumerated types, >> DataModel.xsd (in draft-ietf-xcon-common-data-model) uses xs:string, >> and the string value of the above element is "confirm >> ", which is not one of the allowed values. The >> example should be corrected, or, for preference, the schema in >> draft-ietf-xcon-common-data-model should be changed to use xs:token as >> the base type for join-handling-type and all other enumerated types. >> >> [MB] > Agree that the schema in the data model draft could be improved, by > changing definitions of the enumberated types. Did you send the authors of > that document this comment? Or has that been covered by another apps-team > review? No, would you be so kind? > "confirm" is one of the allowed tokens in the <xcon:floor-request-handling> > element (at least in the latest version -- 27 -- of the data model draft.): > > <xs:simpleType name="floor-request-handling-type"> > <xs:restriction base="xs:string"> > <xs:pattern value="block"/> > <xs:pattern value="confirm"/> > <xs:pattern value=".+"/> > </xs:restriction> > </xs:simpleType> > > The "newline" character was introduced for proper formatting of the document, but we agree that is not allowed per the definition above (<xs:pattern value=".+"/>). So, we should remove the newline. This change likely needs to be done elsewhere in the document. I'm all in favour of readability -- no change will be needed if the schema is changed as suggested above. . . >> 12.3 Media Type Registration >> >> It seems unlikely that the proposed extension of 'ccmpxml' will see >> much use---4 characters seems to be the practical limit for >> extensions. >> > [MB] How about 'ccmp'? Yes. ht -- Henry S. Thompson, School of Informatics, University of Edinburgh 10 Crichton Street, Edinburgh EH8 9AB, SCOTLAND -- (44) 131 650-4440 Fax: (44) 131 651-1426, e-mail: ht@inf.ed.ac.uk URL: http://www.ltg.ed.ac.uk/~ht/ [mail from me _always_ has a .sig like this -- mail without it is forged spam]
- [apps-discuss] apps-team review of draft-ietf-xco… Henry S. Thompson
- Re: [apps-discuss] apps-team review of draft-ietf… Robert Sparks
- Re: [apps-discuss] apps-team review of draft-ietf… Mary Barnes
- Re: [apps-discuss] apps-team review of draft-ietf… Mary Barnes
- Re: [apps-discuss] apps-team review of draft-ietf… Henry S. Thompson