[OSLC-CM] CM 1.0 comments and issues

[Martin Nally]

Here are some comments on the CM 1.0 spec and suggestions of issues to
track for CM 2.0



Query string description


The wording of this section could be improved. Instead of saying
      “Request the Change Request resource at /bugs/bug123 and only the
      properties of title and full owner details.”
We should say:
      “Request the resource that contains only the only the properties of
      title and full owner details of the Change Request resource
      at /bugs/bug123.”
The point is that the URL (including the query string) identifies a new
resource. This resource has a relationship to the resource whose URL does
not contain the query string.



Namespaces


In the example “/bugs/bug123?oslc_cm.properties=dc:title,dc:owner{*}”, dc
appears to have meaning, but it is not clear what it means. Are we saying
that in OSLC URLs of this form, dc always means “㑏
http://purl.org/dc/terms/”? This does not seem to me like a workable
scheme. To make this work, we would need a way to register and endless
number of prefixes. Very few things on the web work this way – IANA is an
exception, but it’s cumbersome. I think this design needs to be revisited.
The obvious alternative is to allow a URI in place of a simple "word" and
to eliminate the "word:word" form.

Managing multi-valued properties and resource links

This design is hard to understand. If I were to issue this request:

GET /records/12234-123344?oslc_cm.properties=blockedBy
Accept: application/xml

I would get back this:

<oslc_cm:ChangeRequest>
    <blockedBy oslc_cm:collref="/records/12234-123344/blockedBy"/>:
</oslc_cm:ChangeRequest>

This response contains no useful information except a “redirect” to another
URL. If I do a GET on that URL ("/records/12234-123344/blockedBy") I would
get this:

<blockedBy oslc_cm:collref="/records/12234-123344/blockedBy">
  <blockedBy rdf:resource="/links/1255-235411" oslc_cm:label="Installation
failures"/>
  <blockedBy rdf:resource="/links/123455-2344" oslc_cm:label="DB setup
fails on 64 bit"/>
</blockedBy>

I see no value in this “redirect”. It would have made much more sense to
return the blockedBy info directly on the first GET:

GET /records/12234-123344?oslc_cm.properties=blockedBy
Accept: application/xml

With response:

<oslc_cm:ChangeRequest>
  <blockedBy rdf:resource="/links/1255-235411" oslc_cm:label="Installation
failures"/>
  <blockedBy rdf:resource="/links/123455-2344" oslc_cm:label="DB setup
fails on 64 bit"/>
</oslc_cm:ChangeRequest>

Nothing would prevent us defining a POST against this URL to INSERT
entries, as defined in the current spec, although without a design to do a
corresponding DELETE and UPDATE, I think the value of this POST is
questionable.

The text is unclear about what "/links/123455-2344" refers to, but says it
is a "link resouce". This appears to suggest that a GET on this URL would
take me not to the OSLC resource that is blocking the change, but some
"link resource" that might in turn point to the resource I'm interested in.
I would not be in favor of this further indirection, but in any case the
spec needs to say what the design really is.



Relative URLs


Many of the URLs used in examples in the spec use relative URLs. This is
strange, because OSLC is about integration between independent tools,
which, lacking special magic, will have different hostnames/ports. The spec
either needs to use absolute URLs in all the examples, or explain how
multiple, independent OSLC tools will share a hostname/port.


Best regards, Martin

Martin Nally, IBM Fellow
CTO and VP, IBM Rational
tel: (949)544-4691
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