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Heather has finished adding in support for Eric's metaRootData package in RootIo. This has yet to be added to a tagged version of GR, but once it is, users can either output ROOT files as they do now, or generate a "meta" ROOT file which identifies the event components associated with each event.
Eric summarized the event collection concept for Dan, and outlined the a GCR use case, where a user may desire to have a special selection of GCR events (where an event is comprised of multiple event components) from a pool of events across data files.
Eric asked if there were plans to synch up xrootd's ..such as at Lyon. Richard states there are no such plans yet.
We would want to store the meta ROOT files in the Data Catalog. They would have a special status and could be utilized to locate events requested by a user. Meta Root files returned to a user may have to be regenerated or updated to take into account the location of the deep copied events into files onto a local machine.
Richard will contact David Chamont to see about adding support for the event collections in the skimmer.
Richard saw two cases:
1.) A SLAC user working on a SLAC machine - where the contents of the meta ROOT file in terms of location of the files would be useful
2.) A user desiring to take his data to his local non-SLAC machine, where the locations of the ROOT files referenced in the meta ROOT file are not necessarily useful.
Final conclusion: We need to have a discussion with Tony where we outline what we desire and he can outline what is possible.