7.11 Semantics Reasoning

Semantic reasoning is a mechanism to derive implicit facts that are not explicitly expressed in the existing knowledge/facts (such as RDF triples) by leveraging a set of reasoning rules. A Semantic Reasoning Function (SRF) is defined in this clause in order to support semantic reasoning functionality in the oneM2M system. The key features of a SRF are shown in Figure 7.11-1:

Figure 7.11-1: Key Features of Semantic Reasoning Function (SRF)

Feature-1: Enabling semantic reasoning related data

The major functionality of Feature-1 is to enable the semantic reasoning related data (referring to facts and reasoning rules) by be discoverable and publishable/sharable across different entities in the oneM2M system (which is illustrated as the dark yellow arrow in the Figure 7.11-1). The semantic reasoning related data can be a Fact Set (FS) and/or a Rule Set (RS):

• A FS refers to a set of facts. For example, a set of RDF triples stored in a <semanticDescriptor> resource can be regarded as a FS. In general, a FS can be used as an input for a semantic reasoning process (i.e. an input FS) or it can be a set of inferred facts as the result of a semantic reasoning process (i.e. an inferred FS).
• A RS refers to a set of semantic reasoning rules. For example, oneM2M applications may define their own reasoning rules (user-defined reasoning rules) for different application needs.

Overall, Feature-1 involves the publishing/discovering/sharing of semantic reasoning related data (including both FSs and RSs) through appropriate oneM2M resources. The general flow of Feature-1 is that oneM2M users (as originators) can send requests to certain receiver CSEs in order to publish/discover/update/delete the FS/RS-related resources through the corresponding CRUD operations. Once the processing is done, the receiver CSE will send the response back to the originator.

Feature-2: Optimizing other semantic operations with background semantic reasoning support

The existing semantic operations supported in the oneM2M system (e.g., semantic resource discovery and semantic query) may not yield desired results without semantic reasoning support. The major functionality of Feature-2 of SRF is to leverage semantic reasoning as a "background support" function to optimize other semantic operations (which are illustrated by the pink arrows in the Figure 7.11-1). In this case, users trigger/initiate specific semantic operations (e.g., a semantic query). During the processing of this operation, semantic reasoning may be further triggered in the background, which is however fully transparent to the user.

Overall, the general flow of Feature-2 is that oneM2M users (as originators) can send requests to certain receiver CSEs for the desired semantic operations (such as semantic resource discovery, semantic query, etc.). During the request processing, the receiver CSE, assuming it supports SRF, can further leverage the reasoning capability. In general, the reasoning capability of the SRF is realized by an underlying semantic reasoner. By leveraging the outputs of semantic reasoning (i.e., reasoning result), the receiver CSE will further produce the optimal result for the semantic operation as requested by the originator (e.g., the semantic query result, or semantic discovery result) and then send the response back to the originator.

Feature-3: Enabling individual semantic reasoning process

oneM2M users (as originators) may also directly interact with the SRF by triggering an individual semantic reasoning process, which is Feature-3 of the SRF. When using this feature, a oneM2M user shall first identify the interested facts (as input FS) as well as the desired reasoning rules based on their application needs. When the input FS and RS are identified, the oneM2M user shall send a request to the SRF for triggering a specific semantic reasoning process by specifying the inputs (i.e. the input FS and RS). The SRF will then initiate a desired semantic reasoning process. Once the SRF works out the semantic reasoning result, it will be returned to the oneM2M users for further usage.