An ABL application in a PAS for OpenEdge instance consists of a session manager that manages multi-session agents. Each agent is an operating system process that launches an ABL Virtual Machine (AVM) and uses it to execute a client application request within a session.

You can write event procedures that are executed during agent or session events (for example, when an agent or session starts or shuts down). The main use of event procedures is to manage user context. Context is any data that needs to be persisted over several interactions between a client application and the service. This includes things like user profile, role information, language preferences, etc.