Main restraints curbing a deep integration of Semantic Sensor Networks (SSNs) with complex and articulated architectures, basically reside in too elementary allowed discovery capabilities. Several studies agree advanced querying and retrieval mechanisms are needed to truly fulfill the potential of the SSN paradigm. The proposed approach presents a novel SSN framework, supporting a resource discovery grounded on semantic-based matchmaking .
Offered contributions are:
An overall framework for the Semantic Web of Things (SWoT)  has been designed in  managing semantic-based annotations of data streams, devices, high-level events and services with a well-defined meaning w.r.t. a shared domain conceptualization (i.e., ontology). An explicative architecture of the proposed framework is depicted in Figure 1. A CoAP-based SSN is composed by several sensors deployed in a given area communicating through a local sink node, acting as cluster head, with a gateway interfacing the network toward the rest of the world.
Each sensor is featured by data oriented attributes, as usual, but also by a semantic annotation describing its characteristics and functions. Sink nodes will allow sensors to register their semantic description as a CoAP resource and embed a lightweight matchmaker enabling ontology-based inferences on annotated metadata. Devices within the SSN can be accessed through CoAP clients or remote applications. In order to support the novel semantic-based resource retrieval, slight extensions were devised to the IETF CoAP and CoRE Link format discovery protocol outlined in [1,2]. They are based only on an innovative usage of standard URI-query attributes and on the addition of new ones. Consequently, the resulting framework is still fully backward compatible: servers which do not support semantics will simply reply to requests returning no resource records.
The effectiveness of the proposed approach is motivated by two case studies regarding: