Re: [CDNi] CDNI Metadata Interface

Hi Susan,

  thanx for the comments, responses inline:

> -----Original Message-----
> From: HeXiaoyan [mailto:hexiaoyan@huawei.com]
> Sent: Tuesday, October 11, 2011 5:28 AM
> To: Kevin J Ma; cdni@ietf.org
> Subject: RE: [CDNi] CDNI Metadata Interface
> 
> Hi Kevin,
> Some quick questions and comments on this draft,
> >The Metadata objects are each associated with a URI within the Domain and
> accessible through any of the Hostnames...
> - Could you further explain or give an example how a metadata is accessed
> by
> a Hostname within the Domain? And a further question is how the data model
> works if a metadata is only associated with a specific Hostname within one
> Doman?

I was assuming that metadata would be valid for all hostnames.  If a hostname
needed separate metadata, a new domain would be required.  I was thinking of
hostname as a first level restriction.  My implementation does something along
the lines of the following (where hostname is checked before metadata lookup):

  domain = get_param_from_query_string(getenv("QUERY_STRING"), "domain")
  if (!db_verify_hostname_for_domain(getenv("SERVER_NAME"), domain))
    return error
  metadata = db_get_metadata_by_uri_domain_agent(getenv("REQUEST_URI"),
                                                 domain, getenv("REMOTE_USER"))
  xml = generate_xml_for_metadata(metadata)
  return xml

> - The relationship between Agent objects and Metadata objects is a
> one-to-one relationship, does this mean one agent can only access one
> Metadata within one Domain?

That is a typo in the doc, good catch, thanx!  It should be one to many.
Each metadata must be associated with a single agent, but an agent can be
associated with multiple metadata.  Agent-1 could have metadatas A, B, and
C, while agent-2 could have a separate value for metadatas A and B, and also
have its own metadata D (that agent-1 does not have access to)

> > The association of each Metadata to an Agent allows different Agents to
> retrieve different Metadata values for a given URI in the given Domain.
> - Don't understand why each Metadata object needs to be bind with an Agent
> explicitly, IMO, whether to return different value to different Agents is
> an
> inside process of the upCDN, what downCDN needs to do is just transmit its
> identifier to the upCDN when retrieve a Metadata.

I think the fact that a uCDN would want/need to give out different values to
different dCDNs requires that there be a way to represent and store that
information.  Having it explicitly in the model, i think, simplifies the
implementation and guarantees that all implementation give this issue proper
consideration.

> - Which entity is responsible for creating the Agent objects within one
> Domain? Does the CP can 'see' the downCDNs and creates corresponding Agent
> objects and other CDNs on the way just transmitted it or each upCDN
> located
> in the cascaded path creates a Agent object for each its downCDN?

This is a good question.  Different agents would need to be create by different
entities, as you mention.  I would expect each CDN to create agents to represent
those (outside that CDN) who need access to the metadata interface.

thanx!

--  Kevin J. Ma

> Thanks.
> Best Regards
> Xiaoyan(Susan) He
> 
> -----Original Message-----
> From: cdni-bounces@ietf.org [mailto:cdni-bounces@ietf.org] On Behalf Of
> Kevin J Ma
> Sent: Friday, October 07, 2011 1:21 PM
> To: cdni@ietf.org
> Subject: [CDNi] CDNI Metadata Interface
> 
> Hi all,
> 
>   Just uploaded a new I-D with a proposed metadata model and API:
> 
>     http://www.ietf.org/internet-drafts/draft-ma-cdni-metadata-00.txt
> 
>   The model takes a rather generic approach to metadata representation
>   to support opaque metadata and addresses some of the security issues
>   associated with metadata retrieval.  Comments welcome.
> 
> thanx.
> 
> --  Kevin J. Ma
> 
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