Resource Preview issues

["Jim Amsden" <jamsden@us.ibm.com>]

Resource Preview 2.0 compatibility raises
a few issues, hopefully a small enough number to be able to address in
a single email.

1. Preview Discovery

OSLC2 does Preview Discovery via GET
on a resource that supports Preview using an Accept: application/x-oslc-compact+xml
header to request the Compact resource representation of the resource.

OSLC3 uses HEAD or OPTIONS on the resource
and gets the URI for the Preview from a Link header. This takes two HTTP
requests. Clients can get the Compact resource in one step by using the
Prefer: return=representation; include="http://open-services.net/ns/core#PreferCompact"
header on the GET to get the Compact resource in a single request.

Discussion: The OSLC2 application/x-oslc-compact+xml
header would be a third way to get the Compact resource. Should all three
be supported, or is the OSLC2 approach actually the simplest and most HTTP
consistent? 

Resolution: I think OSLC2 got this right
and OSLC3 preview discovery is unnecessarily complex. Accept headers are
used to negotiate resource representations, and a Compact resource is an
indirect representation of a resource for display purposes. So I recommend
continuing to use the Accept: application/x-oslc-compact+xml to get the
Compact resource, and eliminate the OSLC3 Link and Prefer headers.


2. Compact Resource Representation

Compact resource is an XML document
in OSLC2, although it may be RDF/XML it should be processed as XML. This
format will also need to be supported and return when the media-type requested
through the Accept header is  application/x-oslc-compact+xml. 

OSLC3 Compact resource representation
MUST be application/json and text/turtle, SHOULD be application/ld+json.

Resolution: add OSLC3 Compact resource
MUST support media-type application/x-oslc-compact+xml in addition to the
JSON and RDF representations. Clients use Accept header to get the representation
they want.


3. Preview Resize message

OSLC2 resize message is "oslc-preview-height:
<newHeight>"

OSLC3 resize message is oslc-resize:
{"oslc:hintHeight": <newHeight>, "oslc:hintWidth":
<newWidth>}
 
Resolution: OSLC3 supports 2 resize
messages, one for just height that would work with 2.0 clients, and one
that includes height and width in the oslc-resize message. OSLC 3.0 clients
would look for both. OSLC3 servers should send just the height message
or both if there is a reason to send height and width information. 




Jim Amsden, Senior Technical Staff Member
OSLC and Linked Lifecycle Data
919-525-6575