Speaker
Dr
Marcin Nowak
(BROOKHAVEN NATIONAL LABORATORY)
Description
The ATLAS event data model will almost certainly change over time. ATLAS must retain
the ability to read both old and new data after such a change, regulate the
introduction of such changes, minimize the need to run massive data conversion jobs
when such changes are introduced, and maintain the machinery to support such data
conversions when they are unavoidable. In database literature, such changes to the
layout of persistent datastructures are known as schema evolution. Possible schema
changes range from simple alterations (e.g., adding a new data member) through
complex redesign of a class to multi-class refactoring of the data model.
ATLAS uses POOL/ROOT as its principal event storage technology and benefits from ROOT
automatic schema evolution. For more complex changes, manual schema evolution is
implemented. The architecture of the Gaudi/Athena framework separates the transient
and persistent worlds by a "conversion" layer. We take advantage of this separation
to allow transformations from stored persistent shapes to an evolving transient
class. ROOT custom streamers may be used to allow migration to an intermediate state
representation model.
Authors
Dr
Arthur Schaffer
(LAL ORSAY)
Dr
David Malon
(ARGONNE NATIONAL LABORATORY)
Dr
Marcin Nowak
(BROOKHAVEN NATIONAL LABORATORY)
Dr
Peter Van Gemmeren
(ARGONNE NATIONAL LABORATORY)
