Hi Mira:

your earlier message seems related to this one to Boaz.

There is probably an elegant solution.

-- Karl
============ sent June 11, 1998
Dear Boaz:

do you have a good algorithm to simultaneously follow
two strategy graphs during the same traversal?

-- Karl

To use strategies as guards in visitor and appc entries:

sg2
   guard sg1 before node code
   // execute code only if node is visited according to sg1

we need to solve the following abstract problem:

Given two strategies sg1 and sg2 with the same source, 
where sg1 is a substrategy of sg2,
a class graph g and an object graph o with node n which is visited
following strategy sg2, determine whether n is in the scope of sg1,
i.e. n is visited by the traversal determined by sg1.

Note: sg1 is a substrategy of sg2 if for all class graphs g:
      PathSet(g,sg1) is a subset of PathSet(g,sg2). 

Note: in the applications the strategy sg1 is often an edge.

The straight-forward approach would be to compute two traversal graphs
tg(g,sg1)=t1 and tg(g,sg2)=t2 and to use both during the object traversal
and to have a distinct token set for each.
(t1 might not be a subgraph of t2!)

We need an answer to the question: "is n in the scope of sg1" repeatedly
as we traverse according to sg2.

Is the algorithm much simpler if sg1 is a one edge graph?