An application that queries or consumes descriptions of VO resources must be able to recognize a resource's support for standard IVOA protocols. This specification describes how to describe a service that supports any of the four typed data access protocols - Simple Cone Search (SCS), Simple Image Access (SIA), Simple Spectral Access (SSA), Simple Line Access (SLA) - using the VOResource XML encoding standard. A key part of this specification is the set of VOResource XML extension schemas that define new metadata that are specific to those protocols. This document describes rules for describing such services within the context of IVOA Registries and data discovery as well as the VO Support Interfaces (VOSI) and service self-description. In particular, this document spells out the essential mark-up needed to identify support for a standard protocol and the base URL required to access the interface that supports that protocol.