CSCE 315 Lecture 4

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Commenting

• Write short summary about what a block of code does
• Include reason if possible
• Comment about something that is used to avoid errors (prevents code deletion
• units for numeric data
• range of allowable values.
• limitations on input data.

Database Systems

Designed to manage very large amounts of data, query that data, and pull out useful information.

• Efficiency
• Reliability
• Ease of access

Create structure (schema), and then populate it with data.

Entity-Relationship Model

• Entities are things
• Entity sets are collections of things
• Attributes are properties of entity sets

Relationships

One-to-One

A team can have One MVP

Many-to-One

a town can have many people in it

Many-to-Many

Senators can sponsor many bills, and a bill can be sponsored by many senators

Attributes can be added to relationsips and relationships can be multi-way:

• Person born in a hospital in a town (set of hospitals or relationship annotated with hospital name)

Generalizations: A Senator is an (isa) Elected official

Keys

Identifying a unique record by a value.

Baseball player identified by Number and Team attributes

Weak key needs help identifying:

• Player plays on a team. Team name on Team entity, number on player.

Avoid redundant data like storing team name on the player when the player is related to a team.

Don't use a separate entity if an attribute will suffice.