The web-service interface that is used for integrating with Control System Studio can also be used by other clients. The protocol used by this web-service is specified in Appendix B, JSON archive access protocol 1.0 . At the moment, this protocol is limited to providing basic information (scalar and array samples of a limited set of types, including some meta-data). In the future this interface is going to be extended, so that it will be possible for each control-system support to use a custom data format.

For some applications, using the web-service protocol might not be a viable solution because the actual sample objects (as internally stored by the control-system support) are needed or high troughput for mass-processing data is required. In this case, there are two options.

The first option is writing a Java application that uses the ArchiveAccessService (or rather its implementation, the ArchiveAccessServiceImpl ) from the cassandra-pv-archiver-server module. This will directly expose the sample objects as they are provided by the control-system support.

The second option is directly accessing the Cassandra database. The layout of the tables (as far as samples are concerned) is described in Appendix A, CQL table layout . Applications accessing the database directly should only read data, never insert new data or update existing data. Ensuring data consistency in a distributed system is very tricky and it is very likely that third-party applications would break the data consistency guarantees carefully protected by the Cassandra PV Archiver.