  This document defines the core components of the Observation data model that
are necessary to perform data discovery when querying data centers for
observations of interest. It exposes use-cases to be carried out, explains the
model and provides guidelines for its implementation as a data access service
based on the Table Access Protocol (TAP). It aims at providing a simple model
easy to understand and to implement by data providers that wish to publish
their data into the Virtual Observatory. This interface integrates data
modeling and data access aspects in a single service and is named ObsTAP. It
will be referenced as such in the IVOA registries. There will be a separate
document to cover the full Observation data model. In this document, the
Observation Data Model Core Components (ObsCoreDM) defines the core components
of queryable metadata required for global discovery of observational data. It
is meant to allow a single query to be posed to TAP services at multiple sites
to perform global data discovery without having to understand the details of
the services present at each site. It defines a minimal set of basic metadata
and thus allows for a reasonable cost of implementation by data providers. The
combination of the ObsCoreDM with TAP is referred to as an ObsTAP service. As
with most of the VO Data Models, ObsCoreDM makes use of STC, Utypes, Units and
UCDs. The ObsCoreDM can be serialized as a VOTable. ObsCoreDM can make
reference to more complete data models such as ObsProvDM (the Observation
Provenance Data Model, to come), Characterisation DM, Spectrum DM or Simple
Spectral Line Data Model (SSLDM).
