We think that the user doesn't need to create multiple decision table graphs in a single project. Instead whenever user creates his/her first decision table, the graph should be generated automatically and should contain all the decision tables available in the project.

When a user opens a decision table, the editor could have a button "Display Linked Tables" which would open the graph.

Then, we could remove the Decision Table Graph from the new Asset list because there would always be just single graph generated automatically and accessible from the asset list and/or Decision Table editor.