High Level Interface to Conditions Data at Belle II

Abstract

The Belle II experiment at the SuperKEKB e ⁺ e ⁻ accelerator is preparing for taking first collision data next year. For the success of the experiment it is essential to have information about varying conditions available in the simulation, reconstruction, and analysis code.

The interface to the conditions data in the client code was designed to make the life for developers as easy as possible. Two classes, one for single objects and one for arrays of objects, provide a type-safe access. Their interface resembles that of the classes for the access to event- level data with which the developers are already familiar. Changes of the referred conditions objects are usually transparent to the client code, but they can be checked for and functions or methods can be registered that are called back whenever a conditions data object is updated. The framework behind the interface fetches objects from the back-end database only when needed and caches them while they are valid. It can transparently handle validity ranges that are shorter than the finest granularity for the validity of payloads in the database. Besides an access to the central database the framework supports local conditions data storage which can be used as fallback solution or to overwrite values in the central database with custom ones.