Adding HLTbase to the list of libraries

[u/mrichter/AliRoot.git] / MUON / READMECDB

$Id$

The Offline Condition DataBase is described extensively on ALICE Offline pages.

Here you'll find only information relevant to the MUONCDB.C macro, which defines
 a set of functions to read/write MUON information to this CDB. Those functions are
  not meant to be used as black boxes. Please have a closer look before using 
  (especially the ones writing to the CDB...)
 
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Calibration data objects
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We've designed generic data containers to store calibration information, 
tailored to the way we usually access MUON tracker data, that is, indexed by the pair (detElemId,manuId). 
This container is called AliMUONV2DStore. You can attach a TObject to every and each pair (detElemId,manuId).
 For the moment, that TObject is generally of AliMUONVCalibParam type, 
 which handles a given number of channels (64 typically) as a group.
 As the class names suggest, both classes are only interfaces. Concrete ones are AliMUON2DMap (used instead of a vector
as detElemId are not contiguous) for the V2DStore, CalibParam1I (VCalibParam storing one integer per channel), and
 CalibParam2F (VCalibParam storing 2 floats per channel).

One exception are the HV values from DCS, which are stored "as they come" from the shuttle-dcs interface, as a TMap, where
 the key is the aliasname (TString), and the value a TObjArray of AliDCSValue.

For trigger, the same virtual container idea applies, except we're using 1D container (AliMUONV1DStore).

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CDB location
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One very important notion is that of the DefaultStorage (which you set with 
 AliCDBManager::Instance()->SetDefaultStorage(path)), which tells the CDB library where
 the CDB is sitting (either locally on disk, or on the grid).

For local tests, path will be most likely = local://$ALICE_ROOT/MUON (i.e. there is, in CVS a slim version of the calibration objects needed
  for running the MUON code), or local://$ALICE_ROOT/SHUTTLE/TestShuttle/TestCDB for Shuttle testing.
 
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Writing to CDB
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 In write mode, this macro was/is used to populate the CDB with fake calibration objects for testing purposes.
Real calibration data will normally be handled by the Shuttle (see READMEshuttle).

writeGains() and writePedestals() functions may be used to populate MUON tracker information,
 and generateTrigger() for trigger parts. 
 
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Reading the CDB
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The actual reading is encapsulated into AliMUONCalibrationData class. 
e.g. to read pedestals for run 4567, one would do :

AliCDBManager::Instance()->SetDefaultStorage(cdbPath);
AliMUONCalibrationData cd(4567);
AliMUONV2DStore* ped = cd.Pedestals();

If you want to plot calibration data (not terribly usefull as it's a really global view), use the plot() function 
 in MUONCDB.C, e.g. :
 
plot(*ped,"pedestal")

which will create 2 histograms : pedestal_0 (mean) and pedestal_1 (sigma).

You might also be interested in the diff() method which generates an AliMUONV2DStore
 containing the difference (either absolute or relative) of two AliMUONV2DStore.