Note: The content in this article pertains to ArcGIS versions 8.x and 9.x. Later versions of ArcGIS may contain different functionality, as well as different names and locations for menus, commands and geoprocessing tools.
In ArcGIS 9.1 and earlier, the following warning may be returned if a relationship class is added to ArcMap using the Add Data button:
"Could not add the specified data object to the map."
If attempting to drag and drop a relationship class to from ArcCatalog to ArcMap, the following warning may be returned:
"A selected item could not be added to the map"
ArcMap does not support loading a relationship class as a data layer.
These warnings do not indicate there is a problem with the relationship class. Relationships exist between spatial objects (features in feature classes), nonspatial objects (rows in a table), or spatial and nonspatial objects. Thus, the functionality of a relationship class is available when objects participating in that relationship class are loaded into ArcMap.
For ArcGIS 10.x, the following document provides steps on creating a relationship class between feature classes containing the objects to relate: Creating a simple relationship class. To explore what objects are related to a particular object in a geodatabase, load the related feature classes or tables into ArcMap, and select a feature using the Identify tool. The objects related to the selected feature is displayed in the Identify dialog box. For more information, refer to Exploring the related objects of an object in a table.