Can someone explain in simple terms to me what a directed acyclic graph is?

Question

Can someone explain in simple terms to me what a directed acyclic graph is? I have looked on Wikipedia but it doesn\'t really make me see its use in programming.

Answer 1

Example uses of a directed acyclic graph in programming include more or less anything that represents connectivity and causality.

For example, suppose you have a computation pipeline that is configurable at runtime. As one example of this, suppose computations A,B,C,D,E,F, and G depend on each other: A depends on C, C depends on E and F, B depends on D and E, and D depends on F. This can be represented as a DAG. Once you have the DAG in memory, you can write algorithms to:

• make sure the computations are evaluated in the correct order (topological sort)
• if computations can be done in parallel but each computation has a maximum execution time, you can calculate the maximum execution time of the entire set

among many other things.

Outside the realm of application programming, any decent automated build tool (make, ant, scons, etc.) will use DAGs to ensure proper build order of the components of a program.