COSI 127b Study Guide - Midterm Guide: Superkey, Arity, Candidate Key
8 Mar 2020
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Document Summary
Data model is a framework for organizing/interpreting data. Key is any set of distinguishing attributes of a relation. Candidate key is any minimal set of possible keys. Union and set difference requires that each relation have the same number of columns with the same domain; needs arity and compatibility. Sql is standard data definition and manipulation language. Operations with null usually result in null, except for count which results in zero. Evaluation order is: from, where, group by, having, select, order by, into. Correlated nested query is query whose inner query references the outer relation. Transactions, or xactions, are atomic either the entire xaction is completed or none of it; execution results in either commit or rollback/abort. Acid properties of xactions are atomicity, consistency, isolation, and durability. Threats are programming error, system failures, and concurrency. Valid swaps include any that involve different elements, and reads of same element. Both read/write and write/write of same element result in conflicts.
