Web of Things describes a set of standards by the W3C for solving the interoperability issues of different Internet of Things platforms and application domains.
Architecture
WoT Thing Description (TD)
A Thing Description describes a virtual or physical device. It can be considered to be the entry point for a Thing. Like the index.html page of a WWW website. It describes all available actions, events and properties of a Thing. As well as all available security mechanisms to access them. The Thing Description in highly flexible in order to guarantee interoperability. Additionally to the standard functionality, it describes, with TD Context Extension, a mechanism to extend the functionality. A Thing Description also contains meta data about a Thing, such as titles and descriptions for the actions, events and properties.
History
Pioneering work in connecting objects to the Web probably started around the year 2000. In 2002, a peer-reviewed paper presented the Cooltown project. This project explored the use of URLs to address and HTTP interact with physical objects such as public screens or printers. Following this early work, the growing interest and implementation of the Internet of Things started to raise some questions about the application layer of the IoT. While most of the work in the IoT space focused on network protocols, there was a need to think about the convergence of data from IoT devices. In particular, rather than looking at "one device one app", researchers and practitioners started envisioning the IoT as a system where data from various devices could be consumed by Web applications to create innovative use-cases. The idea of the Web as an application-layer for the IoT started to emerge in 2007. Several researchers started working in parallel on these concept. Amongst them, Dominique Guinard and Vlad Trifa started the Web of Things online community and published the first WoT manifesto, advocating the use of Web standards to build the application layer of the IoT. The manifesto was published together with an implementation on the Sun SPOT platform. At the same time, Dave Raggett from W3C started talking about a Web of Things at various W3C and IoT events. Erik Wilde published "Putting Things to REST", a self-published concept paper looking at utilising REST to sense and control physical objects. Early mentions of the Web of Things as a term also appeared in a paper by Vlad Stirbu et al. From 2007 onwards, Trifa, Guinard, Wilde and other researchers tried publishing their ideas and concepts at peer-reviewed conferences but their papers got rejected by the Wireless Sensor Networks research community on the basis that Internet and Web protocols were too verbose and limited in the context of real-world devices, where optimisation of memory and computation usage, wireless bandwidth, or very short duty cycles were essential. However, a number of researchers in the WSN community started considering these ideas more seriously. Early 2009, a number of respected WSN researchers such as David Culler, Jonathan Hui, Adam Dunkels and Yazar Dogan evaluated the use of Internet and Web protocols for low-power sensor nodes and showed the feasibility of the approach. Following this, Guinard and Trifa presented their end-to-end implementation of the concepts and presented it in a peer-reviewed publication accepted at the World Wide Web conference in 2009. Building on this implementation and uniting efforts, a RESTful architecture for things was proposed in 2010 by Guinard, Trifa and Wilde. Noticing a growing industrial and academic interest for connecting things to the Web, Guinard, Trifa and Wilde ran the first International Workshop on the Web of Things, WoT 2010 which has been running yearly since. These workshops have become the first forum where a growing community of researchers and practitioners could discuss the latest findings and ideas in the Web of Things. In 2011, two of the first PhD theses on the Web of Things were presented at ETH Zurich: Building Blocks for a Participatory Web of Things: Devices, Infrastructures, and Programming Frameworks from Vlad Trifa and A Web of Things Application Architecture – Integrating the Real-World into the Web from Dominique Guinard. In 2014, the W3C showed an increased interest in the Web of Things and organised the W3C Workshop on the Web of Things, under the lead of Dave Raggett together with Siemens and the COMPOSE European project. This workshop lead to the creation of the Web of Things Interest Group at W3C and the submission of the Web Thing Model.. The same year, Siemens announced the creation of a research group dedicated to the Web of Things. In October 2014, Google also announced their interested in these ideas by launching the Physical Web GitHub project. The Web of Things Interest Group identified the required set of standards needed for the Web of Things in February 2017 . The Working Group has started working on 4 deliverables called WoT Architecture, WoT Thing Description, WoT Scripting API and WoT Binding Templates.
Alternative approaches
A number of alternative approaches to Web standards have been proposed, such as WS-* services, but these were later shown as not necessarily well-suited for real-world things. The Constrained Application Protocol is also quite often cited as an alternative or complementary approach for resource-constrained devices. CoAP shares similarities with the Web of Things architecture such as the use of RESTful resources.
