  This article focuses on the complicated yet still relatively immature area of
the Internet of Things Search Engines (IoTSE). It introduces related concepts
of IoTSE and a model called meta-path to describe and classify IoTSE systems
based on their functionality. Based on these concepts, we have organized the
research and development efforts on IoTSE into eight groups and presented the
representative works in each group. The concepts and ideas presented in this
article are generated from an extensive structured study on over 200 works
spanning over one decade of IoTSE research and development.
