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How the ENVS and QRES stacks work (example)

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Presentation on theme: "How the ENVS and QRES stacks work (example)"— Presentation transcript:

1 How the ENVS and QRES stacks work (example)
3rd Country Conference, February 2007 How the ENVS and QRES stacks work (example) by Prof. Kazimierz Subieta SBA/SBQL pages:

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

3 Execution scenario Dept join avg( ( employs . Emp ) . sal ) join
1st Dept 1st employs 1st Emp 2nd employs 2nd Emp 2nd Dept 3rd employs 3rd Emp join 1st dot 2nd dot avg

4 Sample query Dept join avg( ( employs . Emp ) . sal ) Start empty ENVS
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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