The Data Bookkeeping Service 3 (DBS 3) provides an improved event data catalog for Monte Carlo and recorded data of the CMS experiment. It provides the necessary information used for tracking datasets, for example the data processing history, files and runs associated with a given dataset, and much more.

DBS 3 has been completely re-designed and re-implemented in Python on the basis of a CherryPy based environment for developing RESTful (Representational State Transfer) web services, which is commonly used within the data management and workload management (DMWM) group of CMS. DBS 3 is using the Java Script Object Notation (JSON) dataformat for interchanging information and Oracle as database backend.