CISC 332 Lecture Notes - Lecture 13: Peter Chen, Unique Key
10 Feb 2018
School
Department
Course
Professor
Document Summary
Basic for a number of other models and methods and design tools. A database is modeled as a collection of entities and relationships among entities. Entity - an object that exists and is distinguishable from other objects. Entities have attributes - people have names, addresses, . Entity set - set of entities of the same type that share properties. Relationship set - a mathematical relation among n>=2 entities, each taken from entity sets. An attribute can also be a property of a relationship set. Ex: the date which tracks when the student started being associated with the advisor. Entity sets of a relationship need not be distinct - each occurence of an entity set plays a role in the relationship. Domain - set of permitted values for each attr. Composite can be broken down into parts - ex: a name that is broken down into first, middle, and last.
