A decision-to-decision path, or DD-Path, is a path of execution (usually through a graph representing a program, such as a flow-chart) that does not include any conditional nodes. That is, it is the path of execution between two decisions.

DD (decision-decision)' path is a path of nodes in a directed graph.
A chain is a path in which:

• Initial and terminal nodes are distinct
• All interior nodes have in-degree = 1 and out-degree = 1

A DD-path is a chain in a program graph such that:

• It consists of a single node with in-degree = 0 (initial node)
• It consists of a single node with out-degree = 0 (terminal node)
• It consists of a single node with in-deg ≥ 2 or out-deg ≥ 2
• It consists of a single node with in-deg = 1 and out-deg = 1
• It is a maximal chain of length ≥ 1.