[apps-discuss] apps-team review of draft-ietf-xcon-ccmp-13
ht@inf.ed.ac.uk (Henry S. Thompson) Mon, 16 May 2011 09:04 UTC
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To: apps-discuss@ietf.org, Mary Barnes <mary.ietf.barnes@gmail.com>, Chris Boulton <chris@ns-technologies.com>, Simon Pietro Romano <spromano@unina.it>, Henning Schulzrinne <hgs+xcon@cs.columbia.edu>, Alan Johnston <alan.b.johnston@gmail.com>, Richard Barnes <barnes@bbn.com>, iesg@ietf.org
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Date: Mon, 16 May 2011 10:04:29 +0100
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Subject: [apps-discuss] apps-team review of draft-ietf-xcon-ccmp-13
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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version numbers in _update_ messages (so that the server could reject any update whose target version had been superseded) considered and rejected?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. 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. 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? 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? 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. . . 11. XML Schema An http URI should be provided where this schema document can be found on its own, and an update policy for it (or, preferably, _two_ URIs, one for exactly this schema document, and one which will be updated if this document is revised or superseded). (Likewise for DataModel.xsd and rfc4575.xsd.) 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. 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. A similar problem occurs in the response in 6.3 (floor-request-handling) 6.9 Alice exploits a CCMP server extension For compatibility with the actual response given, the extension schema document should have a target namespace, as follows: <?xml version="1.0" encoding="UTF-8"?> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="http://example.com/ccmp-extension-schema.xsd" xmlns="http://example.com/ccmp-extension-schema.xsd"> <xs:element name="confSummary" type="conf-summary-type"/> <xs:complexType name="conf-summary-type"> <xs:sequence> <xs:element name="title" type="xs:string"/> <xs:element name="status" type="xs:string"/> <xs:element name="public" type="xs:boolean"/> <xs:element name="media" type="xs:string"/> </xs:sequence> </xs:complexType> </xs:schema> Or, better, the example _and_ the schema should be changed to read as follows: <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <ccmp:ccmpResponse xmlns:info="urn:ietf:params:xml:ns:conference-info" xmlns:ccmp="urn:ietf:params:xml:ns:xcon:ccmp" xmlns:xcon="urn:ietf:params:xml:ns:xcon-conference-info" xmlns:example="http://example.com/ccmp-extension"> <ccmpResponse xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="ccmp:ccmp-extended-response-message-type"> <confUserID>xcon-userid:Alice@example.com</confUserID> <confObjID>xcon:8977794@example.com</confObjID> <operation>retrieve</operation> <response-code>200</response-code> <response-string>success</response-string> <ccmp:extendedResponse> <extensionName>confSummaryRequest</extensionName> <example:confSummary> <title> Alice's conference </title> <status> active </status> <public> true </public> <media> audio </media> </example:confSummary> </ccmp:extendedResponse> </ccmpResponse> </ccmp:ccmpResponse> <?xml version="1.0" encoding="UTF-8"?> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="http://example.com/ccmp-extension" xmlns="http://example.com/ccmp-extension"> <xs:element name="confSummary" type="conf-summary-type"/> <xs:complexType name="conf-summary-type"> <xs:sequence> <xs:element name="title" type="xs:string"/> <xs:element name="status" type="xs:string"/> <xs:element name="public" type="xs:boolean"/> <xs:element name="media" type="xs:string"/> </xs:sequence> </xs:complexType> </xs:schema> Otherwise I've checked all the schemas for conformance and the examples for schema-validity. 12.2 XML Schema Registration Should include pointers to the RFCs which include the text of the schema documents named as "DataModel.xsd" and "rfc4575.xsd" in the schema docuemnt given in section 11. 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. Nits: One more proofreading pass over the first three sections would be a good idea. . . 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