ZION: A Scalable W3C Web of Things Directory

The proliferation of non-interoperable smart objects within the Internet of Things (IoT) has led to a fragmented and heterogeneous landscape. The Web of Things (WoT), particularly the W3C WoT, has emerged as a promising solution to this challenge, enabling seamless integration across IoT platforms and domains by extending known web standards. This paper introduces Zion, an open-source scalable W3C Thing Description Directory (TDD) designed to efficiently address the indexing and querying of Thing Descriptions (TDs) and the associated Web Things (WTs). Zion offers a standard API for performing CRUDL operations while supporting metadata querying through JSONPath. We further demonstrate its practical utility through real-world deployments, applying Zion to Structural Health Monitoring (SHM) and integrating it with IoT devices alongside blockchain technology. Comparative analysis with the other TDD implementations complying with the W3C standards - e.g., WoT Hive and TinyIoT - demonstrates that Zion outperforms both. It exhibits response times approximately ten times lower than those observed in the compared TDDs under high workloads.