Background: I am writing a small/partial IDE. Code is internally converted/parsed into a graph data structure (for fast navigation, syntax-check etc). Functionality to undo/redo (also between sessions) and restoring from crash is implemented by writing to and reading from journal. The journal records modifications to the graph (not to the source). Question: I am hoping for advice on a decision on data-structures and journal format. For the graph I see two possible versions: g-a Graph edges are implemented in the way that one node stores references to other nodes via memory address g-b Every node has an ID. There is an ID-to-memory-address map. Graph uses IDs (instead of addresses) to connect nodes. Moving along an edge from one node to another each time requires lookup in ID-to-address map. And also for the journal: j-a There is a current node (like current working directory in a shell + file-system setting). The journal contains entries like "create new node and connect to current", "connect first child of current node" (relative IDs) j-b Journal uses absolute IDs, e.g. "delete edge 7 - 5", "delete node 5" I could e.g. combine g-a with j-a or combine g-b with j-b. In principle also g-b and j-a should be possible. [My first/original attempt was g-a and a version of j-b that uses addresses, but that turned out to cause severe restrictions: nodes cannot change their addresses (or journal would have to keep track of it), and using journal between two sessions is a mess (or even impossible)] I wonder if variant a or variant b or a combination would be a good idea, what advantages and disadvantages they would have and especially if some variant might be causing troubles later.