COOL Overview

The COOL project is one of the three components of the LCG Persistency Framework. Its goal is to provide common software solutions for the storage and management of the conditions data of the experiments installed on the LHC ring at CERN. COOL software development is the result of a collaboration between Atlas and LHCb, the two LHC experiments that have chosen COOL to manage their conditions data, together with the ES group of the CERN IT Department, which also provides the overall project coordination.

Conditions data

In contrast to "event data", which contain information about the response of the detectors to the passage of the particles generated in each interaction of the two collider beams (one event), "conditions data" record the state of the detector at the time when events are collected. While their size is orders of magnitude smaller than that of event data, conditions data are extremely important because they are needed for the reconstruction and analysis of the events taken using the detector they describe.

The main property of conditions data is that they vary with time. Each value or set of values of conditions data describes the state of the detector during a limited lapse of time, and should only be used for the analysis of the events collected during that "interval of validity" (IOV).

In addition to their time variation, certain items of conditions data may also exist in different versions. Examples of these "multi-version" (MV) detector conditions include calibration and alignment data, which are computed by processing large sets of raw event and non-event data using algorithms which may exist in different versions. Only one version of each of these conditions data items must be used for the reconstruction and analysis of event data. Conversely, other items of conditions data, such as detector temperatures and voltages from the detector control systems, only exist in one version because they are raw data produced by direct measurements. These are referred to as "single-version" (SV) conditions data.

More details about the properties of conditions data that are relevant to COOL are given in the Data Model section of this TWiki.

-- AlexLoth - 03-Nov-2009