COSI 127b Lecture Notes - Lecture 3: Serializability, Data Integrity, Referential Integrity

• School: Brandeis University
• Department: Computer Science
• Course: COSI 127b
• Professor: Cherniack

Document Summary

A serializable schedule has the same result as a serial schedule of the same xactions. Ideally, only serializable schedules should be allowed, but it is hard to determine if a schedule is serializable. Therefore, most database systems approximate serializability, such that all schedules must be serializable and without conflicts. Valid swaps include any that involve different elements, and reads of the same element. Read/write and write/write of the same element result in conflicts. Given a precedence graph, a schedule is not conflict serializable when there is a cycle. A relation must be a set (the sql keyword primary key is used). Other possible candidate keys can be declared by using the sql keyword unique. Unlike primary keys, there can be multiple unique keys. Attach constraints to the value of an attribute. The not null keyword will prevent null values. The check keyword will place a condition on an attribute"s value.