Page "Simplified molecular-input line-entry system" Paragraph 7

In terms of a graph-based computational procedure, SMILES is a string obtained by printing the symbol nodes encountered in a depth-first tree traversal of a chemical graph.

The chemical graph is first trimmed to remove hydrogen atoms and cycles are broken to turn it into a spanning tree.

Where cycles have been broken, numeric suffix labels are included to indicate the connected nodes.

Parentheses are used to indicate points of branching on the tree.