Data Persistency Solution for LHCb

The GAUDI software architecture, designed in the context of the LHCb experiment, maintains separate and distinct descriptions of the transient and persistent representations of the data objects. One of the motivations for this approach has been the requirement for a multitechnology persistency solution such that the best-adapted technology can be used for each category of data: raw event data, reconstructed event data, summary event data, detector description, event catalogues, statistical data, etc. This approach has also allowed us to evolve smoothly with time from current legacy persistent data, to more sophisticated solutions that will appear in the future, such as object database management systems. A simple generic mechanism has been developed for converting data between their transient and persistent representations and for resolving, on demand, associations through different persistent solutions. We intend to use this mechanism for ROOT, Objectivity/DB and ZEBRA (legacy) data. We describe the basic concepts, as well as the more detailed design issues of this multi-technology persistent solution. The performance and practical experience in its use will also be presented.