steps in creating a using a relational database:
1. design schema, create schema using DDL
2. bulk load initial data
3. query and modify data

ad-hoc queries in high-level language
query language also used to modify data

queries return relations (compositional, closed)
when you get back the same type of object that you query = closure
compositionality = the ability to run a query over the result of a previous query

query languages
relational algebra – formal
greek symbols!!
SQL – actual (implemented) language