COOL Data Model

The COOL software and its API are based on the data model displayed in the following figure, which reflects the properties of conditions data described in the Overview section.

A "conditions data object" is the smallest atomic entity of conditions data that can be manipulated individually. Every conditions data object refers to a specific conditions data item, such as the alignment of a tracking device or the temperature measured by a sensor. For a given data item, each conditions data object has an interval of validity (IOV) and may exist in more than one version. Note that, with a slight abuse of terminology, a conditions data object is often itself referred to as an IOV.

Data item, interval of validity and version are referred to as the three axes of "metadata" of conditions data in the COOL data model. The actual values of the physical observables associated to a conditions data object (e.g. the actual values of the physical parameters describing the alignment of a tracking device in a given IOV and for a given version of the alignment algorithm) are referred to as the payload of that conditions data object. In the COOL software, a conditions data object is described by implementations of the cool::IObject interface, which encapsulate and make available both its metadata and its payload.

A typical COOL query consists in retrieving from the relevant metadata the conditions data payloads that are needed to process a given set of events.

The three-axes for uniquely identifying each 'conditions data object' in the conditions database
Source: P. Mato, Conditions DB for LHCb, Interface Specification Proposal, February 2000

-- AlexLoth - 16-Dec-2009

-- AndreaValassi - 29-Jun-2010