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M.Ballintijn, J.Bunn and O.Couet CN/ASD
The interactive analysis of high energy physics event data using HBOOK ntuples has always been one of the major strengths of the PAW system. With the design and implementation of the PIAF system and the advent of Column Wise Ntuples (CWNs), the quantity of event data that can be analysed interactively has been significantly increased. Other improvements due to the use of CWNs include the support for more data types and new possibilities for structuring the data. CWNs can store boolean, bit field, integer, real, double precision and character string data types. Data can be structured in arrays of one or more dimensions, with the last dimension of each array being of variable length. This allows for efficient storage of lists of values, lists of vectors etc. The actual length of the array in a given event is defined by another integer variable in the ntuple.
The component of the PAW system responsible for executing queries like ntuple/plot or ntuple/project was previously only partially adapted to handle these new features. Furthermore, this part of PAW lacked stability and robustness, and was hindered by many built-in limitations.
To overcome these deficiencies a new query processor has been developed which removes most limitations of the old system. More importantly, it offers a regular syntax which allows much greater freedom to the user when expressing queries. It also supports all the data types offered by the CWNs in combination with automatic type promotion. The new query language is largely backward compatible, with more powerful alternatives being offered in the few incompatible cases. Non-scalar ntuple variables like vectors and multi-dimensional arrays, possibly of variable length, are fully integrated. Other new features include access to KUIP vectors, and the use of arrays that index other arrays, which allows for more complex structures in ntuples.
The structure of the query compiler allows for optimisations, like static sub-expression evaluation, and reordering of terms based on their complexity. It is foreseen to upgrade the MASK mechanism and to use this to cache the results of cuts (macros).
The new Query Processor will be released in the PRO area at the time of the next Program Library update. Users wishing to try the new Query Processor beforehand (and this is strongly encouraged) will find it integrated in PAW versions in the NEW area in the new year.