Query Evaluation

Overview

1. Parsing, view expansion, and type and authorization checking of $Q$
2. Translation of $Q$ to a formulation $E_Q$ in relational algebra
3. Optimization of $E_Q$
   1. Generates an efficient query plan $P_Q$ from $E_Q$
   2. Uses statistical metadata about the database instance
4. Execution of query plan $P_Q$
   1. Uses access methods to access stored relations
   2. Uses physical relational operators to combine relations

Considerations

• How relations are stored and physically represented
• Choice of physical relational operators to answer complex queries
• How intermediate results are managed

Two-Tier Architecture

Relational Algebra

Query Optimization

Cost Estimation