6.2 <semanticFanOutPoint> Operations

6.2.1 Introduction

The <semanticFanOutPoint> resource is a virtual resource because it does not have a representation. It is the child resource of a <group> resource and shall be targeted only by RETRIEVE requests. When a request (for semantic discovery or semantic query) is sent to the <semanticFanOutPoint> resource the host uses the memberIDs attribute of the parent <group> resource to retrieve all the related descriptors, then proceeds with the corresponding processing.

See clause 9.6.14a in oneM2M TS-0001 [1] for a full description of the resource type. The use of <semanticFanOutPoint> for semantic resource discovery and semantic query is further described in clause 7.4.

6.2.2 Retrieve <semanticFanOutPoint>

The RETRIVE operation on <semanticFanOutPoint> shall be used for two purposes:

performing semantic resource discovery; and
performing semantic query.

The procedure below shall be used for performing a semantic discovery or a semantic query procedure using the descriptor content of all member semantic resources belonging to an existing <group> resource.

Table 6.2.2-1: <semanticFanOutPoint> RETRIEVE for Semantic Resource Discovery and Semantic Query

<semanticFanOutPoint> RETRIEVE
Associated Reference Point	Mca, Mcc and Mcc'
Information in Request message	According to clause 10.1.3 in oneM2M TS-0001 [1]. For the semantic query case, the request message shall include the parameter Semantic Query Indicator, which shall not be included in the request for semantic resource discovery.
Processing at Originator before sending Request	For the semantic resource discovery case, the Originator shall request a semantic discovery to be performed using the content of the semantic descriptors of all member resources belonging to an existing <group> resource. For the semantic query case, the Originator may discover various <group> resources defining different explicit query scopes and select the one having the desired query scope. Then, the Originator shall request a semantic query to be performed using the semantic information of all member resources belonging to this <group> resource. The Originator may be an AE or CSE.
Processing at Receiver	The Receiver shall: Check if the Originator has RETRIEVE privilege in the <accessControlPolicy> resource referenced by the membersAccessControlPolicyIDs in the parent <group> resource. In the case membersAccessControlPolicyIDs is not provided, the access control policy defined for the parent <group> resource shall be used. Upon successful validation, obtain the URIs of all the member semantic resources from the memberIDs attribute of the parent <group> resource. If there are semantic resources stored on different CSEs, individual RETRIEVE requests are sent to each CSE for retrieving the descriptors, otherwise the descriptor attributes are simply retrieved for all the semantic resources hosted locally. All semantic descriptors are accessed based on the respective access control policies. Once all of the related descriptor attributes have been retrieved, the SPARQL request is being executed on the combined content.
Information in Response message	The result of the SPARQL request executed on the content retrieved from the semantic resources_._
Processing at Originator after receiving Response	According to clause 10.1.3 in oneM2M TS-0001 [1].
Exceptions	According to clause 10.1.3 in oneM2M TS-0001 [1].