Distributed data flow

Distributed data flows serve a purpose analogous to variables or method parameters in programming languages such as Java, in that they can represent state that is stored or communicated by a layer of software.

Unlike variables or parameters, which represent a unit of state that resides in a single location, distributed flows are dynamic and distributed: they simultaneously appear in multiple locations within the network at the same time.

[1][2][3] A distributed data flow satisfies the following informal properties.

Formally, we represent each event in a distributed flow as a quadruple of the form (x,t,k,v), where x is the location (e.g., the network address of a physical node) at which the event occurs, t is the time at which this happens, k is a version, or a sequence number identifying the particular event, and v is a value that represents the event payload (e.g., all the arguments passed in a method call).

[1][5] Each distributed flow is a (possibly infinite) set of such quadruples that satisfies the following three formal properties.