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AW: [MAWG-API] Further issues (was: Status code 206)

From: Bailer, Werner <werner.bailer@joanneum.at>
Date: Thu, 22 Dec 2011 09:03:18 +0100
To: Florian Stegmaier <stegmai@dimis.fim.uni-passau.de>, "public-media-annotation@w3.org" <public-media-annotation@w3.org>
Message-ID: <CD9846F872C7874BB4E0FDF2A61EF09FD471FA0AF8@RZJC1EX.jr1.local>
Hi Florian,

> > - multiple identifiers for resources or fragments: In some source formats, it
> could be possible to identify the resource or one of its fragments in multiple
> ways, e.g. by one or more identifiers, fragment name or temporal/spatial
> fragment URIs. In the RDF examples, this can be represented (as
> recommended in the guidelines) by using owl:sameAs. For an API
> implementation, we should require the querying by any of the valid
> identifiers must be supported.
> 
> Sorry, i do not get it - could you please clarify this?

Example: you have a fragment, which has an actual identifier (e.g., a numeric ID in the source document), and there exists a temporal media fragment URI as well. When you query the API for metadata about the fragment using either of the two identifiers, the API should return the same result.

> > - Fragments without identifiers: There are source formats, which may
> contain metadata about a fragment (e.g. a track) without specifying any kind
> of identifier for it. For the test suite, a workaround is to add an identifier, in
> order to ensure a reproducable test result. For the RDF representation this is
> not a problem, as blank nodes can be used.
> > In an actual API implementation, an identifier generated by the API would
> have to be either deterministic or ensured to be valid for a certain time (e.g.
> a session). Consider e.g. the following case: a client requests all metadata for
> a video, and receives also metadata for the audio and video tracks. The tracks
> do not have any identifier in the source file, so the API generated it. If the
> client wants to query other metadata of these tracks later, it has to be
> ensured that the identifiers generated by the API are still valid.
> 
> I agree - we should keep this in mind to add this information to the test suite
> spec.

Not only, as this concerns the behaviour of the API, this should also go into the API doc.

Best regards,
Werner

> -----Ursprüngliche Nachricht-----
> Von: Florian Stegmaier [mailto:stegmai@dimis.fim.uni-passau.de]
> Gesendet: Donnerstag, 22. Dezember 2011 07:08
> An: public-media-annotation@w3.org
> Betreff: Re: [MAWG-API] Further issues (was: Status code 206)
> 
> Hi Werner,
> 
> thank you for these comments, a mostly agree with them!
> 
> > - source format identifiers: The API document should contain a list of
> recommended identifiers for the formats considered in the API document,
> to ensure that uniform values are used for the source format (e.g., "mpeg7"
> vs. "mpeg-7").
> 
> In addition we could link to the identifiers given in the ontology document.
> 
> > - status code 404: The use of this status code also needs clarification. We
> propose the following: 404 should only be used when querying for specific
> properties, in case that one/several of those are not contained in the
> document. When quering for all properties, only those for which values exist
> shall be returned, but not others with status 404.
> 
> +1
> 
> > - multiple identifiers for resources or fragments: In some source formats, it
> could be possible to identify the resource or one of its fragments in multiple
> ways, e.g. by one or more identifiers, fragment name or temporal/spatial
> fragment URIs. In the RDF examples, this can be represented (as
> recommended in the guidelines) by using owl:sameAs. For an API
> implementation, we should require the querying by any of the valid
> identifiers must be supported.
> 
> Sorry, i do not get it - could you please clarify this?
> 
> > - API doc section 4.4.1: fragmentIdentifier is defined as "This attribute
> should be an URI determining the fragment for which the metadata is
> relevant." We propose to be more precise here and require this to be a
> complete URI, not just a fragment part.
> 
> +1
> 
> > - Fragments without identifiers: There are source formats, which may
> contain metadata about a fragment (e.g. a track) without specifying any kind
> of identifier for it. For the test suite, a workaround is to add an identifier, in
> order to ensure a reproducable test result. For the RDF representation this is
> not a problem, as blank nodes can be used.
> > In an actual API implementation, an identifier generated by the API would
> have to be either deterministic or ensured to be valid for a certain time (e.g.
> a session). Consider e.g. the following case: a client requests all metadata for
> a video, and receives also metadata for the audio and video tracks. The tracks
> do not have any identifier in the source file, so the API generated it. If the
> client wants to query other metadata of these tracks later, it has to be
> ensured that the identifiers generated by the API are still valid.
> 
> I agree - we should keep this in mind to add this information to the test suite
> spec.
> 
> > Best regards,
> > Martin and Werner
> >
> >> -----Ursprüngliche Nachricht-----
> >> Von: Florian Stegmaier [mailto:stegmai@dimis.fim.uni-passau.de]
> >> Gesendet: Mittwoch, 21. Dezember 2011 12:38
> >> An: public-media-annotation@w3.org
> >> Betreff: [MAWG-API] Status code 206
> >>
> >> Dear all,
> >>
> >> while creating the JSON responses it was quiet unclear, how the status
> code
> >> 206 should be used. I had a few discussions with Werner and Martin about
> >> this. We have defined it as follows in the spec:
> >>
> >> "206 - Partial Content - only a subset of the available data stored in the
> result
> >> set"
> >>
> >> There are quiet a few ways, how it could be interpreted.
> >>
> >> Currently, code 206 (partial content) seems to be use in cases, where not
> all
> >> fields of the response data structure are filled, as the information was not
> >> present in the source document. IMO this is incorrect due to the following
> >> reasons.
> >>
> >> According to RFC2616, 206 is a partial GET request, i.e. only part of the
> >> existing document is returned. Thus, 206 should in our case only be used.
> If
> >> only part of the information in the source document can be returned. If all
> >> information from the source document is returned, 200 should be used,
> >> even if this does not fill all possible return values.
> >>
> >> It is the usual case, that not all return values can be filled (e.g., language
> for
> >> each and every property). Thus using not OK return code seems very
> >> impractical, as an error status would be the default. Also, many of the
> >> example JSON responses seem to fill these values with a kind of default
> >> (e.g., set language to "en"). This should not be done, as it invents
> >> information that is (i) not in the source document and (ii) optional. In such
> >> cases, the respective attributes should not be returned.
> >>
> >> To make this clear, the definition of this status code should be revised in
> the
> >> API document.
> >>
> >> For the test suite, both files (RDF as well as the examples) have to be
> taken
> >> into account to ensure this behavior of 206. Further, we have to decide
> how
> >> we handle a "known" loss of information. This is the case if we have a
> >> mapping into our core ontology where the according property in the
> source
> >> format is more specific.
> >>
> >> Best regards,
> >> Florian
> >> _____________________________
> >> Dipl. Inf. Florian Stegmaier
> >> Chair of Distributed Information Systems
> >> University of Passau
> >> Innstr. 43
> >> 94032 Passau
> >>
> >> Room 248 ITZ
> >>
> >> Tel.: +49 851 509 3063
> >> Fax: +49 851 509 3062
> >>
> >> stegmai@dimis.fim.uni-passau.de
> >> https://www.dimis.fim.uni-passau.de/iris/
> >> http://twitter.com/fstegmai
> >> _____________________________
> >>
> 
Received on Thursday, 22 December 2011 08:04:14 GMT

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