[CITE-Forum] Resource Oriented Architecture (was: Re: [CITE.SC] Dec 14th Client Testing Webinar)

Arnulf Christl arnulf.christl at metaspatial.net
Wed Dec 15 07:39:42 EST 2010


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Just some thoughts that came to me after John asked a question about how
to test RESTful clients.

Looking at this problem from an architectural point of view (instead of
from a "RESTful software" perspective) the resources are the inportant
entities and there are no clients and no servers but only resources and
representations. In the ideal Resource Oriented Architecture the state
of an "application" is transferred with each request as part of the
resource's representation. This would mean that a (WMS) map that is
returned from a server would simply include a FeatureInfo request "hint"
encoded as a URL - if the service supports querying. The client can use
this "hint" to offer this feature to the user (if the client implements
querying). The user clicks on the map (pixel coordinates) which are
added to the request including the real world coordinates of the map
image (which always need to be delivered together with the response map
from the service - er - the resource state).

The rest is unchanged standard WMS processing, take the local pixel
coordinates + real world coordinates, calculate click position, query
the data, send the representation of whatever was found back to the client.

The important bit in the whole story is that the client does not need
any a priori knowledge of the service to be able to query it - and can
thus not really create "wrong" queries. IUt is being told what it can do
anytime it can do it. In real life we would all expect some intelligence
in the client, if only for convenience. But the interesting bit is that
the test is done way before implmenting any software, it is more like
test driven standard development (if that term did not exist then it was
just invented).

If we go back to unloved Richardson's and Ruby's RestFUL Web Services
book they have a simple recipe how to design RESTful services. It
involves 4 steps:

1. Identify the resources and accordingly define the URIs
2. Deciding the data format for each resource (representations of the
resource).
3. Methods supported at each URI (~which of the 4 HTTP CRUD operations
are supported for each resource).
4. Deciding the response and status code to be returned to the client.

And in more detail -
1. Figure out the data set.
2. Split the data set into resource.
For each kind of resource -
3. Name the resource with URIs
4. Expose a subset of the uniform interface
5. Design the representation(s) accepted from the client
6. Design the representation(s) served to the client
7. Integrate the resource into existing resources, using hypermedia
links and forms
8. Consider the typical course of events: event flow
9. Handle the error conditions (an example error could be an Update to a
resource that does not exist yet).

Step 9 sort of polishes the process off and immediately takes care of
testing. This all happens before we implement any software. For us this
could mean that we standardize the process of designing a resource and
responses instead of designing interface standards, letting them loose
on developers and afterwards ask ourselves how we could test what we
invented.

Talking about "Testing RESTful APIs of OGC service" (which have not been
designed to be RESTful at all) waters down the clear resource oriented
principles quite a bit. They seem to suggest that the request to a
resource could be in a way "wrong" - which is probably a "wrong"
interpretation of the whole REST idea.

Is this only brain damaged nit picking or does it make any sense?

Have fun,
Arnulf.

Luis Bermudez wrote:
> All,
> 
> We had a fantastic session today with about 10 participants. where Chuck Morris from Northrop Grumman presented a client testing capability. The  steps presented were as follows:
> 
> - Following a similar procedure as for a server testing, a new session was started
> - A WMS test suite was selected: OGC WMS client  1.3.0 
> - A form appeared 
> - A get Capabilities URL for an existing server was provided: A WMS service from a local degree installation.
> - A proxy URL was then provided by TEAMEngine to be invoked by the client
> - A client (Gaia) was opened 
> - The client was given the proxy URL
> - Several operations were triggered from the user interface in the client (zoom ,etc..)
> - TEAMEngine reported on the validity of the request perform by the client.
> 
> From the discussion: 
> - Need a set of operations for a client to be tested. 
> - If the client doesn't performed all the expected operations then the report should say so. 
> - The report should also tell about operations that the client performed but that were not tested.
> - Need to do a comprehensive revision to make sure that the current WMS 1.3.0 client CTL tests take into account all the WMS 1.3.0 client-related requirements. 
> - This client testing will be merged to the main code and the test will be available soon in the beta web site.
> 
> The recording is available here:
> https://opengeospatial.webex.com/opengeospatial/ldr.php?AT=pb&SP=MC&rID=19707657&rKey=cf1de92d2f5f2017
> 
> The last 10 minutes of the recording has a discussion about details of the source code, which may or may not be of interest to some folks.
> 
> Cheers !
> 
> Luis
> -------------
> Luis Bermudez
> lbermudez at opengeospatial.org  
> +1 (301) 760-7323 
> 
> The OGC: Making Location Count...
> http://www.opengeospatial.org/contact
> 
> 
> 
> 
> On Dec 14, 2010, at 9:52 AM, Luis Bermudez wrote:
> 
>> All,
>>
>> This is a reminder that we are going to have a CITE Client Testing meeting at 10:00 am, Eastern Standard Time (New York, GMT-05:00) 
>>
>> https://opengeospatial.webex.com/opengeospatial/j.php?ED=148780447&UID=0&PW=NOTcwMGQ5ZjFj&RT=MiMxMQ%3D%3D 
>>
>> meeting password: Cite2010 
>>
>> +1 512 225 3050 passcode:36429# 
>>
>>
>> Luis
>> -------------
>> Luis Bermudez
>> lbermudez at opengeospatial.org  
>> +1 (301) 760-7323 
>>
>> The OGC: Making Location Count...
>> http://www.opengeospatial.org/contact
>>
>>
>>
>> On Dec 9, 2010, at 1:50 PM, Luis Bermudez wrote:
>>
>>> All,
>>>
>>> On Dec 14th we are going to have a webinar at 10 AM eastern time to show case and discuss the latest work related to Client testing done by Chuck Morris from Northrop Grumman. Enclosed is the meeting information. I invite you all interested on this topic to participate.
>>>
>>> Topic: Client Testing 
>>> Date: Tuesday, December 14, 2010 
>>> Time: 10:00 am, Eastern Standard Time (New York, GMT-05:00) 
>>> Meeting Number: 797 435 997 
>>> Meeting Password: Cite2010 
>>>
>>>
>>> ------------------------------------------------------- 
>>> To join the online meeting (Now from mobile devices!) 
>>> ------------------------------------------------------- 
>>> 1. Go to https://opengeospatial.webex.com/opengeospatial/j.php?ED=148780447&UID=0&PW=NOTcwMGQ5ZjFj&RT=MiMxMQ%3D%3D 
>>> 2. If requested, enter your name and email address. 
>>> 3. If a password is required, enter the meeting password: Cite2010 
>>> 4. Click "Join". 
>>>
>>> To view in other time zones or languages, please click the link: 
>>> https://opengeospatial.webex.com/opengeospatial/j.php?ED=148780447&UID=0&PW=NOTcwMGQ5ZjFj&ORT=MiMxMQ%3D%3D 
>>>
>>> ------------------------------------------------------- 
>>> To join the audio conference only 
>>> ------------------------------------------------------- 
>>> +1 512 225 3050 passcode:36429# 
>>>
>>> ------------------------------------------------------- 
>>> For assistance 
>>> ------------------------------------------------------- 
>>> 1. Go to https://opengeospatial.webex.com/opengeospatial/mc 
>>> 2. On the left navigation bar, click "Support". 
>>>
>>> You can contact me at: 
>>> lbermudez at opengeospatial.org 
>>>
>>>
>>> To add this meeting to your calendar program (for example Microsoft Outlook), click this link: 
>>> https://opengeospatial.webex.com/opengeospatial/j.php?ED=148780447&UID=0&ICS=MI&LD=1&RD=2&ST=1&SHA2=d8QzvwbABa3sWVcIU1FluaZBcGcGHlsshXRzPqSTnC8=&RT=MiMxMQ%3D%3D 
>>>
>>> The playback of UCF (Universal Communications Format) rich media files requires appropriate players. To view this type of rich media files in the meeting, please check whether you have the players installed on your computer by going to https://opengeospatial.webex.com/opengeospatial/systemdiagnosis.php 
>>>
>>>
>>>
>>>
>>> http://www.webex.com 
>>>
>>>
>>>
>>> IMPORTANT NOTICE: This WebEx service includes a feature that allows audio and any documents and other materials exchanged or viewed during the session to be recorded. By joining this session, you automatically consent to such recordings. If you do not consent to the recording, discuss your concerns with the meeting host prior to the start of the recording or do not join the session. Please note that any such recordings may be subject to discovery in the event of litigation. 
>>>
>>>
>>>
>>>
>>> Luis
>>> -------------
>>> Luis Bermudez
>>> lbermudez at opengeospatial.org  
>>> +1 (301) 760-7323 
>>>
>>> The OGC: Making Location Count...
>>> http://www.opengeospatial.org/contact
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> CITE.SC mailing list
>>> CITE.SC at lists.opengeospatial.org
>>> https://lists.opengeospatial.org/mailman/listinfo/cite.sc
>> _______________________________________________
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> 
> 
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- --
Nothing makes sense, except we make it.
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