(Project) Graph Algorithm

Terminology: A Graph has Nodes connected by Links (directed from one node to another); Cycle free - application: project tasks. The Links have no attributes. If a Node has no links it is independent of the others; same applies to sets of Nodes. When storing a graph, I reference the other nodes like this class Graph { public nodes: GraphNode[]; } class GraphNode { public id: string; // key public label: string; public prerequisiteId: string; // pointer - the id of the previous node public dependentId: string; // pointer - the id of the following node } (why: ease of entry and retrieval, no need for storing a list; links have no attributes and can be derived on the fly) With this, I can draw most graphs found in project plans with their tasks. e.g. b a< > d c a=starting point b=parallel, starts after a is complete (prerequisite: a, dependent:d) c=parallel, starts after a is complete (prerequisite: a, dependent:d) d=finish, starts after b+c is complete Question A: What graph constructs can I not represent with this model? (please provide images or so) When drawing the graph, I convert the structure to class PaintNode { public id: string; public label: string; public prerequisiteIds: string[]; // pointer list - the id of the previous nodes } The conversion from GraphNodes to PaintNodes is pretty easy. Question B: What is a good algorithm to convert PaintNodes to GraphNodes? (pseudo code is fine in Java or Typescript style) Question C: How can I recognize that the PaintNodes cannot be converted to GraphNodes due to the restriction of the data model? (pseudo code is fine in Java or Typescript style) Follow up project: automatic layout