## 1 Introduction  
The Internet of Things paradigm [1] aims at supporting _smart object_ connectivity so that any physical object (home appliances, cars, products in a small, smartphones, _etc._) can interact with each other in an unmanned-wise manner and provide humans with a better daily experience. Existing technologies like WSN or RFID, among others, are envisioned as foundation technologies for the IoT. To accomplish that task, standards are required, as they will encourage interoperability among devices and solutions from different stakeholders. Several international standardization bodies have increased their activities in the IoT area, as [2] reports. Furthermore, research projects are also heavily involved in specifying and describing reference models, layered architectures, information models, ontologies and so forth, that could be adopted in the near future by the IoT standardization bodies, as well as by the solutions providers. The IoT-A European research project [3] is specifying an architectural reference model [4] that will provide a common framework for IoT-A solutions, overcoming interoperability challenges. Briefly, the proposed model in [4] virtualizes devices to obtain their computational representation. Virtualizing device capabilities provides significant improvements to software architectures as they become decoupled from the specific (proprietary) way the hardware resources are accessed. The virtual representation of the resources provided by a set of devices enables applications from different domains to access seamlessly the same capabilities supported by a shared, heterogeneous hardware infrastructure. Thus, the deployment and maintenance costs of new solutions are reduced. No new duplicating hardware infrastructure is needed, as the already existing solutions are rapidly reused for almost any upcoming application domain. Upgrading systems with new more powerful devices is not likely to impact on the running software solutions, as long as the new devices are virtualized in the same way [5; 6]. The so-called _virtual device_ in IoT-A exposes its semantically described resources to any other actor by means of services, accomplishing a Service Oriented Architecture (SOA) approach [7]. Different SOA technologies are being used and worldwide accepted, but the one becoming preferred for its simplicity and low overload whenever constrained devices are involved is RESTful Web Services, based on the Representational State Transfer (REST) approach [8]. In a Resource Oriented Architecture (ROA) solution, system entities can only create, read, update and delete resources hosted by any other system entity. To save network resources WSN-based solutions are usually event-driven systems. Sensor nodes go into sleep mode until a significant event is triggered, notifying subscribers about it only when necessary. This behavior reduces the energy consumption and the number of messages exchanged across the network, improving the overall performance of the WSN. The design of such systems has to comply with IoT reference models in order to be integrated in any IoT solution. Therefore, the elements in an event-driven system like in a WSN have to be properly modeled to match the REST approach, along with the IoT reference model (e.g., IoT-A). This paper proposes a model that enables REST compliance of event-driven systems, virtualizing the corresponding devices as it is being proposed in IoT reference models like IoT-A. The model has been developed and successfully integrated in a pilot in Web of Objects (WoO), a European research project included in the ITEA2 research program and funded by the Spanish Ministry for Industry, Energy and Tourism. WoO aims at providing a model to develop a Web of Objects, comprised of objects in an IoT environment that cooperate smartly to arrange and provide a web of services and complex virtual devices.