About topology exceptions
This topic applies to ArcEditor and ArcInfo only.
Topology rules may represent an ideal situation, but geodatabases are flexible enough to handle exceptions to the rules found in real-world data. Violations of topology rules are initially stored as errors in the topology, but where appropriate, you can mark them as exceptions. Exceptions are thereafter ignored, although you can return them to error status if you decide that they are actually errors and that the features should be modified to comply with the topology rules.
Exceptions are a normal part of the data creation and update process. An assessor's geodatabase might have a topology rule requiring that building features not cross parcel lines as a quality control for the building digitizing effort. This rule might be true for 90 percent of the features in the city, but it could be violated by some high-density housing and commercial buildings.
If you create a condominium building feature that crosses parcel boundaries, it will be discovered as an error when you validate your edits, but you can mark it as a legitimate exception to the rule. Similarly, a street database for a city might have a rule that centerlines must connect at both ends to other centerlines. This rule would normally ensure that street segments are correctly snapped to other street segments when they are edited. However, at the boundaries of the city, you might not have street data. Here the external ends of streets might not snap to other centerlines. These cases could be marked as exceptions, and you would still be able to use the rule to find cases where streets were incorrectly digitized or edited.