[OSLC] resource: storage vs representation--specifying variations in the form of the return from a GET

Mon Jan 18 14:05:01 EST 2010

Ian/Andy,

In Andy's example, the media type is the same in both cases, i.e. 
application/rdf+xml. It is the content that is different, i.e. requesting 
quartiles (4 quantiles) versus percentiles (100 quantiles). The way to get 
different content is application-dependent. 

In the example, the workflow that initiated the creation of estimate 
should specify the number of quantiles desired. 

Another way to request different content is via query parameters on the 
URL. For example, the application could define a query parameter like so 
to request percentiles:

http://braintwistors.example.com/ems10/Estimate/7263?ems:numberOfQuantiles=100

In this case the service might re-express the estimate as percentiles 
instead of quartiles (presumably by interpolation).

Arthur Ryman, IBM DE
Chief Architect, Rational Project and Portfolio Management
Office: 905-413-3077, Cell: 416-939-5063
Assistant: Nancy Barnes, 905-413-4182 

Ian Green1 <ian.green at uk.ibm.com> 
Sent by: community-bounces at open-services.net
01/18/2010 12:34 PM

To
Andrew J Berner <ajberner at us.ibm.com>
cc
community at open-services.net, community-bounces at open-services.net
Subject
Re: [OSLC] resource: storage vs representation--specifying variations in 
the form of the return from a GET

I don't see these as different representations;  the mediatype defines the 

format, not the content.  it would lead to a proliferation of media types 
were we to use a different one for each of these variants.

best wishes,
    -ian

ian.green at uk.ibm.com (Ian Green1/UK/IBM at IBMGB)
Chief Software Architect, Requirements Definition and Management
IBM Rational

From:
Andrew J Berner <ajberner at us.ibm.com>
To:
Geoffrey M Clemm <geoffrey.clemm at us.ibm.com>
Cc:
community at open-services.net, community-bounces at open-services.net
Date:
18/01/2010 01:41
Subject:
Re: [OSLC] resource: storage vs representation--specifying variations in 
the form of the return from a GET
Sent by:
community-bounces at open-services.net

Good answer, Geoff, that's the usual way for different representations to
be negotiated, so that's a good standard to follow.   And it's just a
string, so we could choose anything we want I suppose for what is "legal"
to request in the ACCEPT header to deal with the variants allowed for each
resource.   That's more or less analogous to the type of a parameter in a
method signature.    So should the OSLC specs then be defining the allowed
values (or formats, if it's not just a simple list of values) for the
ACCEPT header, and how does that get discovered?  Are there tools that 
help
the programmer provide a "legal" value?

Andy Berner
Lead Architect, ISV Technical Enablement and Strategy
IBM Rational Business Development
972 561-6599
ajberner at us.ibm.com

Ready for IBM Rational software partner program -
http://www.ibm.com/isv/rational/readyfor.html

|------------>
| From:      |
|------------>

>--------------------------------------------------------------------------------------------------------------------------------------------------|
  |Geoffrey M Clemm/Lexington/IBM                                   |

>--------------------------------------------------------------------------------------------------------------------------------------------------|
|------------>
| To:        |
|------------>

>--------------------------------------------------------------------------------------------------------------------------------------------------|
  |Andrew J Berner/Dallas/IBM at IBMUS                                     |

>--------------------------------------------------------------------------------------------------------------------------------------------------|
|------------>
| Cc:        |
|------------>

>--------------------------------------------------------------------------------------------------------------------------------------------------|
  |community at open-services.net, community-bounces at open-services.net 
                                              |

>--------------------------------------------------------------------------------------------------------------------------------------------------|
|------------>
| Date:      |
|------------>

>--------------------------------------------------------------------------------------------------------------------------------------------------|
  |01/17/2010 06:53 PM                        |

>--------------------------------------------------------------------------------------------------------------------------------------------------|
|------------>
| Subject:   |
|------------>

>--------------------------------------------------------------------------------------------------------------------------------------------------|
  |Re: [OSLC] resource: storage vs representation--specifying variations 
in the form of the return from a GET  |

>--------------------------------------------------------------------------------------------------------------------------------------------------|

With HTTP, one requests a variant of the representation with the ACCEPT
header.
If one cannot encode the variant information in the ACCEPT header, I
suppose one could define a URL parameter for it.

Cheers,
Geoff

|------------>
| From:      |
|------------>

>--------------------------------------------------------------------------------------------------------------------------------------------------|
  |Andrew J Berner/Dallas/IBM at IBMUS                                     |

>--------------------------------------------------------------------------------------------------------------------------------------------------|
|------------>
| To:        |
|------------>

>--------------------------------------------------------------------------------------------------------------------------------------------------|
  |community at open-services.net                                |

>--------------------------------------------------------------------------------------------------------------------------------------------------|
|------------>
| Date:      |
|------------>

>--------------------------------------------------------------------------------------------------------------------------------------------------|
  |01/17/2010 06:04 PM                        |

>--------------------------------------------------------------------------------------------------------------------------------------------------|
|------------>
| Subject:   |
|------------>

>--------------------------------------------------------------------------------------------------------------------------------------------------|
  |[OSLC] resource: storage vs representation--specifying variations in 
the form of the return from a GET   |

>--------------------------------------------------------------------------------------------------------------------------------------------------|
|------------>
| Sent by:   |
|------------>

>--------------------------------------------------------------------------------------------------------------------------------------------------|
  |community-bounces at open-services.net      |

>--------------------------------------------------------------------------------------------------------------------------------------------------|

An issue that has come up in several of the workgroups I'm attending:  The
storage of a resource may be very different from the XML representation of
the resource you GET from the URL.  The spec defines the representation 
you
GET and PUT, not the underlying storage mechanism.  The XML representation
specified in the OSLC spec may be derived by the server from the data
stored.

This raises a question about the spec:  Have we been specifying ways of
GETting alternate representations of the same resource?  I'm wondering if
there shouldn't be a somewhat standardized way to do this, although the
specifics will be resource dependent.

As I look over some of the specs, it seems we are defining a single XML
format for each resource.  In some cases, that may make sense--the 
resource
IS the XML document.  But in other cases, the resource is more abstract.
Even if we expect the stream returned by an OSLC GET call to always be an
XML document, there may be variations in the XML representation of a
particular resource that could be important to be specified by the 
request.

One example of this is will show up in the Estimation OSLC spec: the
representation of estimated duration (or other key metrics) of a project.
It's not a single number, but rather a probability distribution, so you 
can
say the probability of completing the project in that amount of time. It's
a formalized representation of something like this:  "it's 50% likely we
can complete it in 24 months, but if you want to be 75% confident, plan 
for
35 months and it's barely possible it could take over 4 years.  There's a
25% chance you can get lucky and finish in 16 months, but the 12 month
schedule you asked for is impossible!  The least it will be is 14 months."

Although "probability distribution" is an abstract mathematical construct,
the XML representation that will be in the estimation OSLC spec is a
quantile representation, which will be "good enough" for consumers.  It
will be an XML representation of some of the values of the probability
distribution, but it can be at various granularities.  It will list the
values of the distribution for evenly spaced percentages as a sequence of
values in the XML document--the client can figure out which percentage 
each
represents based on the number of elements and the order of the elements.
Here's an example of the informal description above, based on a similar
example from the WIKI:

            <ems:QuantileFunction

      ems:metric="http://open-services.net/software-metrics/duration"
               ems:unitOfMeasure="month" ems:numberOfQuantiles="4">
               <ems:low>14</ems:low>
               <ems:quantile>16</ems:quantile>
               <ems:quantile>24</ems:quantile>
               <ems:quantile>35</ems:quantile>
               <ems:high>50</ems:high>
            </ems:QuantileFunction>

 Now, for some purposes, a client may want a representation of the
distribution at a fairly high granularity, like the one above, at the 25%,
50% and 75% probabilities, maybe to get a ballpark of how risky the
schedule will be.  For other purposes, a client may want a representation
at a detailed granularity, getting each percentage probability, perhaps to
answer the question, "what's the probability I can finish by Dec 1?" and
get an answer like "68%".  I'll spare you the similar but much longer XML
representation of the same resource (the probability distribution) but 
with
100 quantiles  :-).

This is just an example; I suspect each workgroup has examples like this,
where there can be different levels of detail or other variations returned
by a GET, all formatted by the interface provider from the same abstract
resource.  It's related, but not quite the same I think, as the standard
issue of "partial retrieves" in queries (which I've started to hear
described as the "shape of the returned set").  So there needs to be a way
for the consumer to negotiate with the provider, or, more simply, just 
tell
the provider how the consumer wants the resource represented, even if all
the representations are in XML.

Even though the "choices" of representation are resource dependent (e.g.
"number of quantiles" for a probability distribution), is there a general
technique we'll use in the various OSLC specs to specify requested
variations?

Andy Berner
Lead Architect, ISV Technical Enablement and Strategy
IBM Rational Business Development
972 561-6599
ajberner at us.ibm.com

Ready for IBM Rational software partner program -
http://www.ibm.com/isv/rational/readyfor.html

_______________________________________________
Community mailing list
Community at open-services.net
http://open-services.net/mailman/listinfo/community_open-services.net

_______________________________________________
Community mailing list
Community at open-services.net
http://open-services.net/mailman/listinfo/community_open-services.net

Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU

_______________________________________________
Community mailing list
Community at open-services.net
http://open-services.net/mailman/listinfo/community_open-services.net

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://open-services.net/pipermail/community_open-services.net/attachments/20100118/1fa716c0/attachment-0003.html>