Database seminars: Mondays @ 4:30 pm https://db.cs.cmu.edu/seminar2022
Database: Collection of inter-related data.
Database systems: Software that stores and analyzes information in a database.
Early DBMS: Expensive computers mean tight coupling between physical and logical layers.
Relational Model: Database abstraction based on relations with physical implemention left up to DBMS. Relational model is independent of any query language implementation. SQL is the de facto standard.
Relation: Unordered set that contain relationship of attibutes. No duplicate tuples.
Tuple: A set of attribute values. Identified by a relation's primary key. In practice, there is auto-generation of unique integer keys.
Relational calculus: Query specifies only what data is wanted.
Relational algebra: Query specifies high level strategy to find the desired results.
- SELECT - Relation with a subset of tuples that satisfies a selection predicate.
- PROJECTION - Generate a relation with only specified attributes.
- UNION - Relation that contains all tuples that appear in either one or both.
- INTERSECTION - Relation with tuples that appear in both.
- DIFFERENCE - Relation with tuples that appear in first but not second relation.
- PRODUCT - Relation with all possible combinations of tuples.
- JOIN - Relation that contains all tuples that contains all tuples that are a combination of two tuples with a common value for one or more attributes. This is different from INTERSECTION because in JOIN, schemas do not have to be the same.