Keyphrases
- expressive power
- closure properties
- query language
- data complexity
- first order logic
- context free grammars
- natural language
- computational properties
- relational algebra
- transitive closure
- grammatical inference
- context free
- relational calculus
- aggregate functions
- constraint query languages
- databases
- relational query languages
- context sensitive
- data management
- programming language
- np hard
- search algorithm