ACIS 1504 Lecture Notes - Lecture 13: Foreign Key, Unique Key, Data Model

• School: Virginia Tech
• Department: Accounting and Information Systems
• Course: ACIS 1504
• Professor: Jean Lacoste

Document Summary

Source data- most of data bases have 20-100 tables, most tables probably have 20-50 column in them/fields. Data model or logical representation of database/how we are going to store our data. That controls how we are going to get it out. Each box is going to be an entity. Name of entity at top ex: customer and order. Each field shows up at lower part of box ex: customer id first name last name email for customer. *****asked on exam how to complete one, pick out primary key and foreign key (foreign key customer id) Crows foot and 1 on outside of line = maximum. Can start on left side (l to r), says a single customer record can be related to 0 or many order records. Read erd, a customer has a minimum of zero and max of many orders. An order may belong to a minimum of one and maximum of one customer.