Question

I have a graph of components and relations between them. User start navigation with a root component. He click expand button on component to reveal new component that are related to current component.

The problem is when user decide to collapse a node. I have to choose a sub-tree to hide and at same time leave graph in consistent state so that there is no expanded node with missing relation to another node in graph.

Now in case of cyclic/loop between component i have difficult of choosing sub-tree. For simplicity i choose the order in which they were expanded. So if a A expand into B and C collapsing A will hide the nodes and edge that it has created. Now consider following scenario.

[-] mean expanded state and [+] mean not yet expanded. A is expanded to reveal B and C. And then B is expanded to reveal D. C is expanded which create a link between C and exiting node D and also create node E. Now user decide to collapse B. Since by order of expansion D is child of B it will collapse and hide D. This leave graph in inconsistent state as C has edge to D but D is not anymore there if i remove CD edge it will still be inconsistent. If i collapse C. And E is again a cyclic link e.g to A will produce the same problem.

    /-----B[-]-----\   
A[-]                D[+]
    \-----C[-]-----/
              \
               E[+]

So guys any idea how can i solve this problem. User need to navigate through graph and should be able to collapse but i am stuck with problem of cyclic nodes in which case any of node in loop if collapse will leave graph in inconsistent state.

Answer 1

If a child node knows how many parents are linked to it, you could let a child node only collapse itself when there’s only one parent connected.

Extrapolated to your example

• Collapsing B would ask node D to collapse.
• Node D does not collapse because it has two parents
• B removes the link to D (leaving D with only one parent)
• If now node C asks D to collapse, it will collapse itself.