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H ow the ENVS and QRES stacks work (example)

H ow the ENVS and QRES stacks work (example). 3rd Country Conference, February 2007. by Prof. Kazimierz Subieta subieta@pjwstk. edu .pl http://www.ipipan.waw.pl/~subieta SBA/SBQL pages: http://www.sbql.pl. Query addressing a tiny database.

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H ow the ENVS and QRES stacks work (example)

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  1. How the ENVS and QRES stacks work (example) 3rd Country Conference, February 2007 by Prof. Kazimierz Subieta subieta@pjwstk.edu.pl http://www.ipipan.waw.pl/~subieta SBA/SBQL pages:http://www.sbql.pl

  2. Query addressing a tiny database • Query: For each department get its reference and the average sal of its employees. • SBQL: Deptjoinavg(employs.Emp.sal) • Tiny database: • Expected result: bag{ struct{i17, 2500}, struct{i22, 1450} }

  3. Execution scenario Deptjoin avg( ( employs . Emp ) . sal ) 1stemploys 1stEmp 1stDept 2ndemploys 2ndEmp 2ndDept 3rdemploys 3rdEmp avg join 1st dot 2nd dot

  4. Sample query Deptjoinavg((employs.Emp). sal) Start Emp(i1) Emp(i5) Emp(i9) Dept(i17) Dept(i22) empty ENVS QRES

  5. In closing … • Please note that this evaluation scenario concerns the formal semantics only, executed by an abstract machine. • Our goal is clear, universal and free of ambiguities semantic specification rather than performance. • In real implementation there are many obvious optimizations. • C.f. our implementations in various projects. • The evaluation process is also the subject of many sophisticated optimizations (rewriting, indices, caching,…) . • The entire process is executed in main memory, hence the computations are not critical. • Critical computations concern the access to external storage and network, and avoiding unnecessary (redundant) computations. • This is just the subject of major SBA optimization methods.

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