Chapter 7. Managing Entities

All entities have a parent, and may have children. The parent of the Broker is called the System Context. It has no parent.

Entities have one or more attributes. For example a name, an id or a maximumQueueDepth

Entities can be durable or non-durable. Durable entities survive a restart. Non-durable entities will not.

Attributes may have a default value. If an attribute value is not specified the default value is used.

Attributes values can be expressed as a simple value (e.g. myName or 1234), in terms of context variables (e.g.${foo} or /data/${foo}/).

Each entity has zero or more context variables.

The System Context entity (the ultimate ancestor of all object) has a context too. It is read only and is populated with all Java System Properties. Thus it can be influenced from the Broker's external environment. See QPID_OPTS environment variable.

When resolving an attribute's value, if the value contains a variable (e.g.${foo}), the variable is first resolved using the entity's own context variables. If the entity has no definition for the context variable, the entity's parent is tried, then its grandparent and so forth, all the way until the SystemContext is reached.

Some entities support state and have a lifecycle.