In SDF, all computation and data communication is scheduled statically. That is, algorithms expressed as SDF graphs can always be converted into an implementation that is guaranteed to take finite-time to complete all tasks and use finite memory. Thus, an SDF graph can be executed over and over again in a periodic fashion without requiring additional resources as it runs. This type of operation is well-suited to digital signal processing and communications systems which often process an endless supply of data. An SDF graph consists of nodes and arcs.
Nodes represent operations which are called actors .
When an actor executes, it always produces and consumes the same fixed amount of tokens. The flow of data through the graph may not depend on values of the data. Because of the second rule, the data that an actor consumes is removed from the buffers on the input arcs and not restored. However, the actors may contain these constructs because the scheduling of an SDF graph is independent of the what tasks the actors do. The notation means that when A executes, it produces 20 tokens.