5.7. Specifying Events
An event is modelled by a procedure, usually having one or more parameters. In this section, we first focus on the kernel events that change the state of the database.
An event is always atomic , but it should also be minimal. An event procedure should specify the least action that leaves the system in a consistent state. For example, an event procedure might change a candidate’s Postal Address, but not both the candidate’s Personal Name and Postal Address, because this can safely be split into two more primitive actions. Conversely, an event shouldn’t be too small: updating only the first line of an address might leave the system in an inconsistent state, in which the address as a whole is invalid. If, owing to a previous ...
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