The W3C Web of Things (WoT) is intended to enable interoperability across IoT platforms and application domains. Overall, the goal of the WoT is to preserve and complement existing IoT standards and solutions. In general, the W3C WoT architecture is designed to describe what exists rather than to prescribe what to implement.

This WoT Discovery specification...

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Introduction

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Terminology

This specification uses the following terms as defined here. The WoT prefix is used to avoid ambiguity for terms that are (re)defined specifically for Web of Things concepts.

Discovery
In the WoT context, the process of finding and retrieving Thing metadata in the form of Thing Descriptions for Things satisfying some criteria of interest.
Exploration
A discovery mechanism that provides access to detailed metadata in the form of one or more Thing Descriptions. Exploration mechanisms are in general protected by security mechansism and are accessible only to authorized users.
Introduction
A "first contact" discovery mechanism, whose result is a URL that references an exploration mechanism. Introduction mechanisms themselves should not directly provide metadata, and in general are designed to be open.
Thing Description Directory (TDD)
A directory service with a prescribed API that allows the registration, management, and search of a database of Thing Descriptions. Note that the acronym should be TDD, not TD, to avoid confusion with Thing Descriptions (TDs).

Use Cases

Examples of why we need discovery.

Requirements

The WoT discovery process should have the following capabilities:

System

Data Management

Security

Privacy

Alignment with Existing Standards

Architecture

Two-Phase approach.

Introduction Mechanisms

Description of supported introductions, and requirements for new introduction mechanisms.

Direct

Any mechanism that results in a single URL. This includes Bluetooth beacons, QR codes, and written URLs to be typed by a user. A GET on all such URLs MUST result in a TD. For self-describing Things, this can be the TD of the Thing itself. If the URL references a Directory, this MUST be the TD of the Directory service. A Directory can be distinguished from a Thing by the use of an @type including the semantic term WoT-Directory.

DNS-SD

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CoRE Resource Directory

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DID Documents

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Exploration Mechanisms

Description of supported explorations, and requirements for new exploration mechanisms.

Self-description

Mechanism for devices to self-describe, hosting their own TDs.

Directory

Mechanism for TDs to be hosted in a searchable directory service.

Information Model

Description of conceptual data organization in a directory.

Directory Service API

API of directory service.

Registration

Sub-API to register a TD (or a link).

Management

Sub-API to manage existing records, and perhaps other functions.

Notification

Sub-API to notify clients of events, such as updates to TDs.

Security and Privacy

Minimum security and privacy requirements for confidentiality, authentication, access control, etc.

Security and Privacy Considerations

Security and privacy are a cross-cutting issues that need to be considered in all WoT building blocks and WoT implementations. This chapter summarizes some general issues and guidelines to help preserve the security and privacy of concrete WoT discovery implementations. For a more detailed and complete analysis of security and privacy issues, see the WoT Security and Privacy Guidelines specification [[?WOT-SECURITY]].

Recent Specification Changes

Changes from First Draft

Acknowledgments

Special thanks to X, Y, and Z for their contributions to this document.

Many thanks to the W3C staff and all other active Participants of the W3C Web of Things Interest Group (WoT IG) and Working Group (WoT WG) for their support, technical input and suggestions that led to improvements to this document.