After digits are extracted and clustered, the clusters are put into a persistent cluster container. These clusters should point back to ther constituent digits in a persistent manner.
This is a general problem and we wait for guidance from the database group. It seems likely we will need an indexing scheme for the muon digits so that we can turn a reference or pointer to a muon digit into an integer which can be written to disk and then converted back into a reference or pointer when the clusters are read back into memory.