Keyphrases
- query language
- database query languages
- query processing
- query answers
- query evaluation
- user queries
- efficient processing
- query containment
- consistent query answering
- response time
- aggregate functions
- semantic information
- expressive power
- data sources
- preference relations
- complex queries
- query logs
- sparql queries
- aggregate queries
- formal semantics
- qualitative preferences
- query formulation
- database queries
- web search engines
- information retrieval
- query answering
- answering queries
- integrity constraints
- retrieval systems
- attribute values
- relational calculus
- null values
- user preferences
- multi dimensional
- data structure