SECONDO : an extensible DBMS architecture and prototype
We describe S ECONDO , an extensible DBMS platform suitabl e for building research prototypes and for teaching architecture and impl ementation of database systems. It does not have a fixed data model, but is open for im plementation of new models. S ECONDO consists of three major components which can be used together or independently: (i) the kernel, which offers query processing over a set of implemented algebras, each offering some type constructors and operators, (ii) the optimizer, which implements the essential part of an SQL-lik e language, and (iii) the graphical user interface which is extensible by viewers fo r new data types and which provides a sophisticated viewer for spa- tial and spatio-temporal (moving) objects. Examples of algebras implemented in S ECONDO are rela- tions, spatial data types, R-trees, or midi object s (music files), each with suitable operations. The kernel is extensible by algebras, the optimizer by optimization rules and cost functions, and the GUI by viewers and display functions. A highlight of the description is a new algor ithm for conjunctive query optimization which is remarkably simple, yet performs very well. We al so emphasize a technique for selectivity estimation suitable for an extensible envi ronment with complex algebras for non-standard data types.
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