Database
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What is a data model?
An abstract model of which things to store and what information about them should be recorded
Define an entity in the context of a database
A thing about which data is to be stored
What are attributes in a database?
Characteristics or other information about entities
How are databases structured?
Databases are formed of tables which are used to store multiple entities
What does each row in a database table typically represent?
Each entity
What is an entity identifier?
An attribute given to each entity which is unique within that table
How can multiple attributes form an entity identifier?
Some database tables have multiple attributes which are combined to form the table’s entity identifier
What is the purpose of an entity description?
To describe how information is to be stored about entities
What is a primary key?
An attribute that provides a unique identifier for every entity in a database table
What is a foreign key?
An attribute in a table which is the primary key in another, related table
What is a link table?
A new table created when linking many-to-many relationships
What is database normalization?
The process of organizing a database to minimize redundancy and improve data integrity
What is the main goal of normalizing databases?
To ensure that entities contain no redundant or repeated data
What are the advantages of a normalized database?
Faster searching and sorting, easier maintenance, minimized duplication, improved data consistency
What characterizes a database in first normal form?
Must not contain any repeating attributes and has atomic data
Define second normal form in databases
Must satisfy first normal form and have any partial key dependencies removed
What is a partial key dependency?
Occurs when a non-key attribute doesn’t depend on the whole of the composite key
What conditions must a database meet to be in third normal form?
Must conform to second normal form and have no non-key dependencies
What does it mean when non-key attributes depend on the key?
All non-key attributes depend on the key, the whole key, and nothing but the key
What are the three possible degrees of relationship between tables in a database?
• one-to-one • one-to-many • many-to-many
Describe a one-to-one relationship with an example
Each car has one owner, and each owner has one car
Describe a one-to-many relationship with an example
Each driver can drive many different cars. Each car is driven by many different drivers
Describe a one to-many relationship with an example
Each car has many passengers. Each passenger sits in one car
What does an entity relationship diagram represent?
Graphically represents the relationships between tables in a database