Dear All,
Thanks for your extensive feedback on the various issues that we have
been discussing on this list, it has been really valuable for the
project team to get this input. We have, we think, identified 3
particular issues of contention:
1/ Whether the Statement should be embedded in the Deposit Receipt or be
a separate document referenced in an atom:link element
2/ Whether to use OAI-ORE for the Statement format or an Atom Feed (as
per CMIS and GData)
3/ How the client and server should negotiate over the format of the
content returned by the edit-media link (EM-URI)
The project team has gone through each of these issues carefully, and
attempted to extract the simplest solutions but with a view to keeping
the SWORD 2.0 specification quite open at this stage, so that community
best practices can actually inform the standard itself in the long run.
Therefore, we're proposing the following approaches to these issues:
1/ Whether the Statement should be embedded in the Deposit Receipt or be
a separate document referenced in an atom:link element
If the Statement is to be embedded in the Deposit Receipt, then it needs
really to be in OAI-ORE form, for the purposes of being clear foreign
markup. Nonetheless, bearing in mind that there is a question as to
whether the Statement should be an Atom Feed, it is clear that this
solution will not be adequate by itself. We therefore propose that the
standard provided to the project's funded developers to code against
says that an OAI-ORE serialisation MAY be embedded in the Deposit
Receipt (the Deposit Receipt will not be required to meet the OAI-ORE
spec for being a resource map itself).
Alongside - or instead - of this, there MAY be one or more atom:link
elements in the Deposit Receipt which link to an external Statement.
These atom:link elements can specify their type attribute to say whether
they are an application/rdf+xml or application/atom+xml;type=feed. It
will be a requirement of the spec that there MUST be an embedded
Statement or at least one separate Statement.
Therefore, you may see a Deposit Receipt like:
<atom:entry>
<atom:link rel="http://purl.org/net/sword/terms/statement";
type="application/rdf+xml" href="http://....."/>
<rdf:RDF>
<!-- ORE statement goes here -->
</rdf:RDF>
</atom:entry>
2/ Whether to use OAI-ORE for the Statement format or an Atom Feed (as
per CMIS and GData)
Another good reason for the approach in (1) is that this means we can
provide different Statement URIs with different type attributes. We
plan to ask developers to produce an ORE and an Atom Feed Statement
format under the project funding. So you may see a Deposit Receipt like:
<atom:entry>
<atom:link rel="http://purl.org/net/sword/terms/statement";
type="application/rdf+xml" href="http://....."/>
<atom:link rel="http://purl.org/net/sword/terms/statement";
type="application/atom+xml;type=feed"
href="http://....."/>
<rdf:RDF>
<!-- ORE statement goes here -->
</rdf:RDF>
</atom:entry>
The combination of approaches in (1) and (2) may seem woolly or
indecisive, but we believe that we can't determine in advance which of
these approaches is better, and that it should be up to the community of
users and implementers to decide which approach works best based on
actual usage of the developed software. Therefore, while the burden of
implementation is placed on the funded portion of the project, we expect
community driven implementations/usages to favour one approach over
another (possibly taking into account things like compatibility with
GData and CMIS, or preferring the more semantic web approach of ORE).
We can then use this information later in deriving a SWORD spec which is
based on best practices.
3/ How the client and server should negotiate over the format of the
content returned by the edit-media link (EM-URI)
The Content Negotiation issue arises from the fact that AtomPub requires
at most one edit-media URI with a given type to be available in the Atom
Entry (Deposit Receipt). Since the SWORD server may contain multiple
files rather than the one file that AtomPub assumes, what this EM-URI
returns under GET is unclear. We initially considered 2 approaches:
a/ A separate HTTP header like Accept-Packaging to allow content
negotiation on a package format
b/ A separate HTTP header like Accept-Media-Features to allow general
content negotaiton on feature sets
As we discussed, both of these have pros and cons, and none of the
approaches to doing this are marked by any best practices, which makes
the project team unwilling to commit to anything too complex or
substantial, at a risk to the simplicity and overall success of SWORD.
Instead we are suggesting adopting a much simpler approach:
The Deposit Receipt can contain already contain a sword:package element
(as per SWORD 1.3), and SWORD 2 plans to allow an arbitrary number of
such elements. These elements will describe the packaging formats
supported by the server, so the client will know in advance what the
capabilities of the server are. Therefore, instead of engaging in a
content negotiation process, the client will just specify a separate
HTTP header indicating what package format should be returned. Whether
this header re-uses the Packaging header used during deposit or
specifies a new header has yet to be decided.
Hopefully these approaches make sense to the group. We are interested
in how you think these will go down both during the project and beyond
in the community, and if there are any obvious problems with what we're
proposing here as the way forward for SWORD.
All the best,
Richard
(On-Behalf-Of the SWORD project team)
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