Ports implement the data flow between components as a publish/subscribe model. Ports have a name and a type. They can be either out ports (for publishing data) or in ports (for subscribing to a sibling out port).

Ports are by default single ports, i.e. they define one type of exported data. The optional multiple qualifier can be used to define a 'dynamic list' of ports of the given type, instead of a single slot. Suchs ports are accessed as an array indexed by strings. In this case, ports are created or destroyed dynamically be the codels. The IDL mappings section for ports explains how this is done.