Exam 1 Database Management Flashcards
What is the goal of an information system?
Add Value to the User
To create an information system one must first understand?
The Business and the Information Needs of the User
Methodology
Build Models of the System
Models
Provide a representation of reality - Communicate with Users
Database Design
Two Steps - Conceptual Model and Implementation Model
Relational Database
Collection of related Entities/Tables
Table
Attributes/Columns, Rows/Instances
Association
A relationship between two or more entity classes
Attributes have data domain
An attributes set of possible values
Entity instance related to another entity instance
ex, An employee works in one department - Each department can work on many different products
Generalization Questions
Do we include the primary key that exists in the sub-classes as an attribute when we total the sum of attributes by adding the parent class to the sub class
-Disjointed vs. Non-Disjointed
Reflexive Relationship
Ex. An Employee can also be a manager
1 manager manages 1 or * workers
Therefore this is an association of an entity class back onto itself
Aggregation
Sales can have many items every item can exist in many sales
-Aggregation = One sale consisting of a set of items being sold
Computed Attributes
ex. Employee(Name, DateofBirth, /Age, Phone
{Age = Today - DateofBirth}
Entity classes describe the business rules of an organization - T/F
True
