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SOEs are only supported for extending map and image services. Because map and image services use a service definition file and do not access a map document (MXD) directly, there are certain classes you should avoid and others you should favor when writing SOEs.
Avoid using ArcObjects from the Carto library that are specifically designed for use with MXDs. This includes IMap, ILayer, and items related to data frames and page layouts. Instead, use ArcObjects designed for working with map services, such as MapServer, MapLayerInfos, and MapDescription. Use the interface IMapServerDataAccess to access the datasets underlying each layer in your map.
Libraries not directly related to the map document, such as ESRI.ArcGIS.Geometry and ESRI.ArcGIS.Geodatabase for .NET or com.esri.arcgis.geometry and com.esri.arcgis.geodatabase for Java, are always permissible to use in SOEs. ...
