Athena Developer Guide

Athena
Chapter 12 N-tuple and Event Collection facilities Version/Issue: 2.0.0
Listing 12.3 Job options for writing out an event collection
1: ApplicationMgr.OutStream = { "Sequencer/EvtCollection" };
2:
3: EvtCollection.Members = { "EvtCollectionWrite/Selector",
"EvtCollectionStream/Writer"};
4: Writer.ItemList = { "/NTUPLES/EvtColl/Collection" };
5: NTupleSvc.Output = { "EvtColl DATAFILE='MyEvtCollection.root'
OPT='NEW' TYP='ROOT'" };
12.3.2 Reading Events using Event Collections
Reading event collections as the input for further event processing in Athena is transparent. The main
change is the specification of the input data to the event selector:
Listing 12.4 Connecting an address tag to an n-tuple.
1: EventSelector.Input = {
2: "COLLECTION='Collection' ADDRESS=’Address’
DATAFILE='MyEvtCollection.root' TYP='ROOT' SEL='(Ntrack>80)'
FUN='EvtCollectionSelector'"
3: };
These tags need some explanation:
• COLLECTION
Specifies the sub-path of the n-tuple used to write the collection. If the n-tuple which was
written was called e.g. "/NTUPLES/FILE1/Collection", the value of this tag must be
"Collection".
• ADDRESS (optional)
Specifies the name of the n-tuple tag which was used to store the opaque address to be used to
retrieve the event data later. This is an optional tag, the default value is "Address". Please
use this default value when writing, conventions are useful!
• SEL (optional):
Specifies the selection string used for the first stage pre-selection. The syntax depends on the
database implementation; it can be:
• SQL like, if the event collection was written using ODBC.
Example: (NTrack>200 AND Energy>200)
• C++ like, if the event collection was written using ROOT.
Example: (NTrack>200 && Energy>200).
Note that event collections written with ROOT also accept the SQL operators ’AND’
instead of ’&&’ as well as ’OR’ instead of ’||’. Other SQL operators are not
supported.
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