Classification of available contributions
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Table 1 - Contributions using CN and their characteristics (Blank: not known).
Composite Capabilities/Preferences Profile (CC/PP) and WAP UAProf are descriptions of device capabilities and user preferences. [66] describes an implementation of HTTP content negotiation that uses them to provide the best variant. We believe that the proactive style of CN is used and, according to our characteristics, the dimension is capacity, the headers are used to convey constraints, and the protocol is HTTP.
The paper [16] presents a decision engine capable of determining optimal adaptation decisions from interpolating situational contextual information, e.g., device capacity. HTTP was used by embedding the userid in the URL to identify the end user.
Istex is a French scientific archive [67]. The clients have the possibility to have the representation in several formats and for that, as mentioned on the site, an ARK is used. If we request the resource without specifying the media type, we receive a json file describing the existing variants and therefore we can consider it a reactive negotiation. The dimension is the media type and the transmission in ARK using the HTTP protocol.
Web archives play a major role in providing a picture reflecting the state of the Web at a given time. The contribution [52] involves the client request in the Memento aggregation process beyond the specification of a URI-R and a date as described in [38] using the header prefer. Therefore the characteristics are: Version for dimension, headers for constraint transport, and HTTP as the protocol and because the aggregator returns a set of records and the client can potentially manipulate the response to issue another request, we judge this part to have a reactive CN style.
One scenario described in the contribution [44] is of a client that requests a resource representation from a server and wants the response to be encoded according to a specific RDF presentation, which is done by including metadata in the request header. And because this contribution is primarily intended for constrained devices, the proactive + adaptive style is preferable. It is important to mention that the content negotiation styles are not mutually exclusive. The author points out that, although this method has been implemented in HTTP, it could easily be defined as equivalent CoAP options.
Using the MarkLogic [67] server, a REST application developer uses the conditional CN style. A client would receive a response with a body containing several parts separated by a delimiter to be selected. This method is primarily used to select the media type dimension and uses HTTP and headers to convey this constraint. In addition, the Open Connectivity Foundation (OCF) specification also includes the means to negotiate the media type using the CoAP protocol [56].