SmartThings The scale and scope of the worldwide web has been in part driven by the availability of HTML as a common serialization, data model, and interaction model for structured resources on the web. By contrast, the general use of appropriate hypermedia techniques for machine interfaces has been limited by the lack of a common format for serialization and exchange of structured machine resources and sensor/actuator data which includes or embeds standardized hypermedia controls. The IRTF Thing to Thing Research Group [T2TRG] has a charter to investigate the use of REST design style [REST]for machine interactions. The W3C Web of Things Interest Group [W3C-WoT] are investigating abstract hypermedia controls and interaction models for machines. Machine optimized content formats exist for web links [RFC5988] [RFC6690] and for data items [I-D.ietf-core-senml]. Structured data which contains both links and items is known as the collection pattern. This draft describes media types for representation of machine resources structured as collections. A simple, reusable data model is described with a representation format, using a well known set of keywords to expose hypermedia controls, which inform clients how to perform state transfer operations on resources. The underlying assumptions regarding transfer layer processing are specified in this document. The HSML media type described in this document is compatible with SenML and CoRE Link-format by reusing the keyword identifiers and element structures from these content formats. Representations of HSML document content may be obtained in CoRE Link-Format and SenML content formats.