COMM 335 Lecture : Class 4 - Introduction to Database.pdf
Document Summary
Non unique primary keys - using first/last name as pk. Foreign key name does not correspond to the actual data (a pk called custid, is called custname in another table) Duplicate data across two tables (first/last name of a customer in two tables) Note: while it is possible to have a database with 1 table that fulfills all the user requirements, lots of duplication will occur (anomalies) Entity relationship diagram is a technique to model real objects in a database. Database users, builder, designer refer an object with different terms, such as: For the purpose of this course we will use crow"s feet notation. An artist could have 0 to many songs, a song can only have one artist. Entity: person, object, event, concept the user environment about which organization wishes to maintain data. For accounting databases: people are often involved (student, customer) Attributes: properties within the entity (last/first name of a customer)
