The component interaction (CI) domain models systems that blend data-driven and demand-driven styles of computation. As an example, the interaction between a web server and a browser is mostly demand-driven. When the user clicks on a link in the browser, it pulls the corresponding page from the web server. A stock-quote service can use a data-driven style of computation. The server generates events when stock prices change. The data drive the clients to update their displayed information. Such push/pull interaction between a data producer and consumer is common in distributed systems, and has been included in middleware services, most notably in the CORBA event service. These services motivated the design of this domain to study the interaction models in distributed systems, such as stock-quote services, traffic or weather information systems. Other applications include database systems, file systems, and the Click modular router.
An actor in a CI model can be active, which means it possesses its own thread of execution. For example, an interrupt source of an embedded system can be modeled as an active source actor. Such a source generates events asynchronously with respect to the software execution on the embedded processor. CI models can be used to simulate and study how the embedded software handles the asynchronous events, such as external interrupts and asynchronous I/O.