How to work with conditions data
There is a quite versatile mechanism to handle conditions data in a unified way in Marlin, MarlinTPC and stand-alone tools.
Some Basics
Conditions data comprises all kind of data that is gathered (usually asynchronously) alongside your event data, calculated during reconstruction, as well as settings of the (experimental or simulated) system, for example:
- Gas conditions
- Field settings
- Pad/channel mapping
- Correction factors
- Electronics settings
- (In principle even geometry information in gear format (according to a statement by Frank Gaede))
- etc.
All data is stored in LCIO Generic Objects, that in turn can be stored in slcio-files or (by means of LCCD) in special conditions data bases. For more convenient data handling special conditions data objects are created, that take care of the somewhat clumsy operation of the raw Generic Objects. For the TPC these data objects are stored in the subdirectory tpcconddata in MarlinTPC. As these conditions data objects were designed back in 2006 or so, some of them are meanwhile quite dated, impractical to use, or have even never been used. They are kept for compatibility, but new ones can be added and have partly been envisaged already.
How to use it
Detailed information on how to use the objects in a Marlin(TPC) processor or in a stand-alone tool (e.g. a tool writing conditions data from the slow control system or a converter) can be found in:
http://www.desy.de/~rdiener/files/conddbmysql_howto.pdf
The document also explains how to set up your own conditions data base, which may be practical for your own lab experiments instead of using slcio files, and how to use the central conditions data base for the Large Prototype experiments.
Storing conditions data in a unified way in a central data base for the Large Prototype experiments has the advantage, that all information about the experiment is available for the reconstruction in a defined way. It avoids the problem of invalid, missing or difficult to use conditions data, compared to keeping it in logbooks or simple text files.
Visualizing the Database
There is a tool to graphically visualize the various stored objects' time structure in a database. A short guide to that can be foun d at: