For the most part, database integrity checks are built into the system and it should not be possible to put invalid data into the database. However in some cases, whether for reasons of complexity or for some other reason, some database integrity problems are not caught by the system. There are also questionable cases; situations where the acceptability of the data is dependent upon circumstances. In these cases it is useful for the system to provide a warning and allow the user to decide whether a problem really exists. It is for these reasons that the warning sub-system exists.

The warning sub-system provides a means by which the system can be supplied with arbitrary queries which validate data integrity. These queries are stored and, when activated, report arbitrary problems with the database's data integrity, either warning conditions or errors. Errors are always reported when the warning system is activated. Individual warnings reported by the supplied queries are then manually sorted into one of the following categories: unclassified (the default), labeled “resolved”, or deferred until a later date. When the warning system is activated unclassified warnings are reported, “resolved” warnings are not reported, and deferred warnings are not reported until the current date reaches the deferral date.

Unlike the database integrity checks built into the rest of the system which report problems immediately as data is inserted into the database, the warning system does nothing until activated.

The warning system is activated by use of one of the supplied functions, causing one or more of the stored queries to check the state of the database.