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Redesign of framework for layer/graph division/merge support
Summary
Detach connectivity information such as in/out edges from the node. Using adjacency list/matrix to represent the connectivity.
Motivation
Current design is not valid when nodes/edges are used by different graphs/layers. For instance, in/out edges are stored inside the node object, which become invalid if multiple graphs/layers are using the same set of nodes. The shortest path algorithm will not work for some graphs and the only way to do it is to create distinct nodes/edges for each graph. Also, current design does not allow multiple edges between same set of nodes. One spatial point can not represent multiple nodes (can be a house/water pipeline node/road end) too.
Design Detail
Maintain a global layer (invisible to the users). All reachable layers are subset of this layer. Each sublayer maintains its own adjacency matrix/list to represent the graph. In other words, connectivity information goes with each layer instead of the node itself. Merging/Splitting graphs/layers simply means creating new adjacency list from the old one. Node/edge itself can stay intact.The other benefit is that by representing graphs with adjacency list/matrix makes it easier to hook to other graph libraries.
Drawbacks
Rewrite basically everything.
Rationale and Alternatives
See above No rationale, just passion