[Fiware-ngsi] NGSI-10 RESTful binding draft

[laurent.artusio at orange.com]

Dear Tobias,

 

We understand that your REST binding contains modifications and extensions to the actual NGSI-10 specification.

 

Here are our comments and understanding for every row of the 2.1.1 table related to every paragraph of your document:

 

2.2 Context element container

We understand this method as being like updateContext, but instead of providing an array of full ContextElement structures, a single entityId structure that belongs to a ContextElement is provided and used as the key.

 

First, it seems the "Base URL" column lacks the needed /{contextElementID}. Secondly, the "context element container" is a resource update, which means the PUT method would be more adapted in a REST style interface. But we think you've chosen the POST method because it certainly allows to return a payload, which is needed by the updateContext NGSI method (it is supposed to return an array of ContextElementResponse).

 

2.3 Individual context element

Looks equivalent to the queryContext method without restriction, with a single entityId and without attributeList. This returns everything for a particular contextElementId. We don't understand what is meant by contextElementId: is it the id field of the EntityId data structure ? Because we don't know if it's possible for HTTP GET to carry XML payload. Therefore the id has to be a simple string if no XML payload is allowed in GET(but we're not sure)

2.4 Attribute of individual context element

Looks equivalent to the queryContext method without restriction, with a single entityId and with a single attribute in the attributeList array. Therefore, shouldn't  the response be a single ContextElementResponse instead of the suggested QueryContextResponse ?

 

2.5 Attribute domain of individual context element

Can be considered as a brand new method, as it is capable of returning all attributes of a specific domain. It does not look possible to do that in actual NGSI-10. We think it is a good feature.

 

2.6, 2.7, 2.8 Type related features

Looks like new features. Have no equivalent in actual NGSI-10. We don't exactly understand what a type is. Is it the "type" field of EntityId data structure ?

 

2.9 Context query resource

We understand it as an exact http mapping of the queryContext method, the HTTP POST payload containing the input parameters, and the HTTP POST response containing the optional output ContextElementResponse array.

 

2.10 Subscription container

Same as above: we understand it as an exact http mapping of the subscribeContext method.

 

2.11 Subscription

Depending on the HTTP verb: modify a subscribing if the HTTP PUT verb is used, or delete a subscribing if the HTTP DELETE verb is used. These are respectively equivalent to the updateContextSubscription method and unsubscribeContext method. 

 

But does the HTTP protocol allow the PUT and DELETE method to carry a response payload as described in your document ?

 

2.12 Notification

We understand it as an exact http mapping of the notifyContext method.

 

Conclusion:

We are aware of the difficulty of making a REST mapping for NGSI, since NGSI it is not natively related to a resource oriented architectural style. NGSI is a classical API with its methods. Therefore it is likely it won't be really possible to convert it into "real REST". It is disappointing because a REST-styled architecture really fits the need of the internet of things, with possibly tree-like representations of "things" mapped to HTTP URIs.

 

We provide an attached NGSI-9-10 class diagram, for any useful purpose. Feel free to tell us a good place to paste it in the wiki.

 

Best regards,

 

Laurent and Laurence

 

De : fiware-ngsi-bounces at lists.fi-ware.eu [mailto:fiware-ngsi-bounces at lists.fi-ware.eu] De la part de Tobias Jacobs
Envoyé : vendredi 13 janvier 2012 09:08
À : fiware-ngsi at lists.fi-ware.eu
Objet : [Fiware-ngsi] NGSI-10 RESTful binding draft

 

Dear members of the OMA NGSI mailing list of FI-WARE,

 

In the end of last year NEC has created a draft version for a RESTful NGSI-10 binding specification which I would like to present here, please see docfile in the attachment. 

 

I am looking forward to receive comments/questions on this. 

 

Best regards

Tobias

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