Connectivity Framework Annex E : Assessment Template : CoAP
E . 6.4 Functional Viewpoint E . 6.4.1 Core Framework Layer Functions
Data Resource Model
( Section 4.1.1 )
ID & Addressing ( Section 4.1.2 )
Data Type System ( Section 4.1.3 )
Data Resource Lifecycle ( CRUD ) ( Section 4.1.4 )
State Management ( Section 4.1.5 )
Publish-Subscribe ( Section 4.1.6 )
Does it provide a data resource model ? Summarize the salient aspects .
CoAP provides a data resource model , following the approach taken by HTTP . A data object is represented via a resource , formatted as a uniform resource identifier ( URI ) path string that is meaningful in context of the server . CoAP defines a core set of methods , GET , POST , PUT , DELETE that can be applied to the resources on a server . Resource representation returned by a server provides the context and links to other resources . It is up-to to the application architects to define the representations and the resource organization , to drive the application state .
CoAP servers can expose resource representations in a variety of formats using a variety of data models . CoAP servers can use the CoRE link format for the resource representations . The CoRE link format identifies the paths to the resources in the CoAP server and provides annotations to the resources , which includes items like the content-type , interface and the resource type . CoAP clients can use these annotations to better understand the semantics of the resource .
Does it provide a way to identifying and addressing data objects ? Summarize the identification and addressing scheme .
The CoAP resource URI path string provides a way of identifying and addressing a data object within a server . The server itself is addressed as a network IP address and port number . The result of combing the URI with the network endpoint is a Uniform Resource Locator ( URL ), expressed as “ coap ://” or “ coaps :// ( when DTLS is used for security ). Does it provide a data type system ? Summarize the salient aspects .
CoAP does not dictate a specific data type system to define resources . CoAP simply transports resources as a payload on CoAP messages . However , the CoRE link format does provide target attributes for CoAP servers to report the content type of the resource .
Does it provide a means of managing a data object ’ s lifecycle ? Summarize the salient aspects .
CoAP provides a means for managing data object lifecycles . A client can use the POST or the PUT method to create a data object ; the GET method to retrieve the data object ’ s representation ; the PUT method to update a data object ’ s representation ; and the DELETE method to delete its representation . The server controls which methods are applicable on a data object , via the response for each operation .
Does it provide a means to manage the recent history of data objects ? Summarize the salient aspects .
CoAP does provide cache mechanisms for proxies and CoAP clients to maintain responses of previous requests . These responses may contain the representations of the resources or links of where the resources are located . The CoAP specification defines mechanisms for determining the freshness of the caches and provides rules for access control and applicability of a cached response .
Does it provide a means to publish and subscribe the state of data objects ? Summarize the salient aspects .
CoAP provides a way to observe ( subscribe ) resources and get notifications when their state changes . The OBSERVE is an extension of the GET method with an additional option that requests the server to keep the representation updated over time . It is up-to to the server to determine how and when to notify the client of updates to resources . There is an IETF effort in progress to develop a publish-subscribe broker on top of this mechanism .
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