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Despite the parent-child hierarchy, picos can be arranged in a heterachical network for peer-to-peer communication and computation. As mentioned, picos support direct asynchronous messaging, sending requests and events to other picos. Picos have an internal event bus for distributing those messages to rules installed in the pico. Rules in the pico are selected to run based on declarative event expressions. The pico matches events on the bus with event scenarios declared in the event expressions. Event expressions can specify simple, single-event matches, or complicated event relationships with temporal ordering. Rules whose event expressions match are scheduled for execution. Executing rules may raise additional events. More detail about the event loop and pico execution model are available elsewhere.
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