Data Structures Task Force, Minutes, Feb. 5, 2002, 08:00 PST, VRVS, Venus

Present: Heather, Toby, Traudl, Michael K, Tracy, Hiro T,  Sasha, Leon

Toby gave a presentation of the GParticle class.

• GParticle was adopted over the traditional vertex/particle model because it was thought to be easier to understand and use.
• Inherits from HepLorentzVector
• There are no explicit vertices; these are implied in the links.
• Mass is included because an unstable particle can have a mass other than the PDG value.
• All links are single, except for parent<->(first) child.
• Methods are important, for example, a smart constructor that does all the links.
• There are some associated structures, for example, the list if steps if there was multiple scattering.

Traudl presented her proposal. She outlines the reasons for preferring this model over the current one (v4r1). Most, if not all of her objections were with respect to this (current) one, not the Gismo model.

• In this model the MC tree is represented by the links (particles) and nodes (vertices), which is supposed to parallel the G4 model.. 
• Having vertices as separate objects make traversing the structure more straight-forward.
• Having the same information in more that one place isn't a good idea, especially if the structures will be used in an interactive environment. (Could be fixed with smart constructors?)

She also produced a UML for v4r1. It became pretty obvious during this discussion that we don't really know what the current model is supposed to mean.  Rumor has it that Richard knows.

• After the meeting, Traudl did some work on v4r1.  Here is the new  UML, and here are her comments.

Traudl asked again how we plan to associate Hits/Digis with particles, and also reconstructed tracks with particles. 

• there was some discussion of the use of some kind of relational table (Gaudi associator, or equivalent in new Gaudi, C++ map?) to do this. Everyone agreed that the relation should be stored separately from the objects themselves.
• Also, there was some sentiment in favor of making up some use cases for the different models. I've made up some for GParticle. (I'm not positive that they work!)

Action Items:

• Toby will report on the G4 particle/vertex structure
• Traudl will report on the Atlas particle/vertex structure
• Leon will try to find out what the v4r1 particle/vertex structure really means.
• In view of the item below, we might want to hold some smaller meetings of the interested parties to try to sort out the MCParticle question.

Next meeting: Our next regular meeting would be on Feb. 19, but this in in the middle of the G4 Workshop at SLAC, so this might not be such a good idea. (Who will be attending this meeting?)