Dataflow

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Dataflow is a term used in computing, and may have various shades of meaning.

Software architecture[edit]

Dataflow is a software architecture based on the idea that changing the value of a variable should automatically force recalculation of the values of variables which depend on its value.

Dataflow embodies these principles, with spreadsheets perhaps the most widespread embodiment of dataflow. For example, in a spreadsheet you can specify a cell formula which depends on other cells; then when any of those cells is updated the first cell's value is automatically recalculated. It's possible for one change to initiate a whole sequence of changes, if one cell depends on another cell which depends on yet another cell, and so on.

The dataflow technique is not restricted to recalculating numeric values, as done in spreadsheets. For example, dataflow can be used to redraw a picture in response to mouse movements, or to make a robot turn in response to a change in light level.

One benefit of dataflow is that it can reduce the amount of coupling-related code in a program. For example, without dataflow, if a variable Y depends on a variable X, then whenever X is changed Y must be explicitly recalculated. This means that Y is coupled to X. This means that the update operation must be explicitly contained in the program and eventually checking must be added to avoid cyclical dependencies. Dataflow improves this situation by making the recalculation of Y automatic, thereby eliminating the coupling from X to Y. Dataflow makes implicit a significant amount of computation that must be expressed explicitly in other programming paradigms.

Dataflow is also sometimes referred to as reactive programming.

There have been a few programming languages created specifically to support dataflow. In particular, many (if not most) visual programming languages have been based on the idea of dataflow.

Distributed data flows have also been proposed as a programming abstraction that captures the dynamics of distributed multi-protocols. The data-centric perspective characteristic of data flow programming promotes high-level functional style of specifications, and simplifies formal reasoning about system components.

Hardware architecture[edit]

Hardware architectures for dataflow was a major topic in Computer architecture research in the 1970s and early 1980s. Jack Dennis of MIT pioneered the field of static dataflow architectures. Designs that use conventional memory addresses as data dependency tags are called static dataflow machines. These machines did not allow multiple instances of the same routines to be executed simultaneously because the simple tags could not differentiate between them. Designs that use Content-addressable memory are called dynamic dataflow machines by Arvind. They use tags in memory to facilitate parallelism. Data flows around the computer through the components of the computer. It gets entered from the input devices and can leave through output devices (printer etc.).

Concurrency[edit]

A dataflow network is a network of concurrently executing processes or automata that can communicate by sending data over channels (see message passing.)

In Kahn process networks, named after Dr. Gilles Kahn, the processes are determinate. This implies that each determinate process computes a continuous function from input streams to output streams, and that a network of determinate processes is itself determinate, thus computing a continuous function. This implies that the behavior of such networks can be described by a set of recursive equations, which can be solved using fixpoint theory. The movement and transformation of the data is represented by a series of shapes and lines.

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