1. A method of processing information representing a graph, comprising: serializing each of multiple statements; using a digital processor to independently compute a hash value for each of the multiple statements; and applying a commutative function to each hash value, to obtain an aggregate hash value representing all of the multiple statements.
1. A method of processing information representing a graph, comprising: serializing each of multiple statements; using a digital processor to independently compute a hash value for each of the multiple statements; and applying a commutative function to each hash value, to obtain an aggregate hash value representing all of the multiple statements. 6. A method according to claim 1 , further comprising: identifying a secret key; and using the digital processor to digitally sign a value dependent upon both of an aggregate hash value and the secret key.