Software Architect's Handbook

Consistency

After a transaction takes place, all of the data must be in a consistent state. This property ensures that all transactions maintain data integrity constraints, leaving the data consistent. If a transaction leaves data in an invalid state, the transaction is aborted and an error is reported. For example, if you had a column with a check constraint that states a column value must be greater than or equal to zero (so as not to allow negative numbers), the transaction would fail if it attempted to insert or update a record with a value less than zero for that particular column.