The ASAP approach [11] describes a structure as a set of axioms that hold between certain paths through the structure. An axiom can be one of the three forms:-
Here RE1 and RE2 are regular expressions over the language of directions. The approach is tailored more towards describing when two nodes are disjoint, rather than providing a unique identity for each node. As a consequence a variety of structures can be described, which can be statically analysed where compile time knowledge is incomplete.