Robert Lupton has requested that the first sequence number in a visit be added to the visit dimension record definition in the gen3 registry schema. We also wish to store the group_id to allow grouping of visits.

In the general case this will allow a user to specify a dataId for the raw that can also be used to obtain the calexp so long as they are specifying the first raw and not the second raw.

day_obs is already in the visit definition.

There are some caveats:

• If a registry has multiple visit_system definitions the day_obs+seq_num may not be able to uniquely identify a calexp.
• Visit definitions use the exposure dimension record (they do not look at files) so determining the first sequence in the visit depends on all the visit members being ingested.

To make this robust I think ObservationInfo is going to have to be modified to have the first_seq and end_seq concepts from CAP-763 – this would require that we also change the exposure dimension record to include first_seq and end_seq since without the former we can't define the visit and without the latter the tooling can't warn about possible missing exposures in the visit definition.