Likewise when a Payables Invoice is Validated, then you may want to create an accounting entry. In this case the "Invoice Validation" is an "Event Type". And your accounting rules for Invoice Validation will be attached against this specific "Event Type".
For Payables, an INVOICE transaction and a PAYMENT transactions are known as Entities within SLA.
Entities can be subdivided into various "Event Classes", for example Credit Memo, Debit Memo, Expense Reports, Invoices etc.
Further to this, against the Event classes we define Event Types, for example, whenever your Invoice is validated or cancelled or adjusted, you may want some specific accounts in the General Ledger to be impacted. Event types are therefore the types/list of events against transactions which you wish to account for in General Ledger.
This is explained in the diagram below.