Structured annotations (or SAs), introduced in the :doc:`2008-09 schema </schemas/september-2008>`, are a general way to extend OME-XML with additional structured information. They can express a variety of data types and linkages, and serve as a replacement for the Custom Attributes and Semantic Type Definitions functionality of prior schemas.
For more information on SAs from an OMERO-centric perspective, see the :omero_doc:`OMERO page on structured annotations <developers/Model/StructuredAnnotations.html>`.
Map Annotations, storing 'key-value pairs', are a type of Structured Annotation which were introduced in the :doc:`/schemas/january-2015`. Further information is available in the :omero_doc:`OMERO developer documentation on Key-value pairs <developers/Model/KeyValuePairs.html>` and a :omexml_downloads:`sample OME-XML file <mapannotation.ome.xml>` is also available.
The structure of the SA used in the schema is shown below, along with all the possible attachment points in the model.
The StructuredAnnotation branch of the OME Model
All points in the OME Model that can be Annotated