Relational Data Model: Lesson 3 Flashcards
What is the advantage of a table?
It has structural and data independence
What is a group of related entities?
Entity set
What is the attributes specific range of values?
It is the attributes domain
What are the 2 important properties in a relational model?
Degrees and cardinality
What is a relational schema?
It is the textual representation of the database tables
What is the primary key?
It is an attribute that uniquely identifies any given entity(row)
What key is composed out of more than 1 attributes?
Composite key
What is a key attribute?
It is any attribute that is part of a key
A key that uniquely identifies each row is called what?
A superkey
What is a candidate key?
It is a superkey without redundancy
What is a foreign key?
An attribute whose values match primary key values in the related table
What is a foreign key used for?
To establish relationships between two tables
What is referential integrity?
FK contains a value that refers to an existing valid tuple (row) in another relation
What is a secondary key used for?
Key used strictly for data retrieval purposes
What is a data dictionary?
Provides detailed accounting of all tables found within the user/designer-created database
What does the data dictionary contain?
Contains all the attribute names and characteristics for each table in the system Contains metadata (data about data)
What is the index key used for?
Points the data location identified by the key
What is a unique index?
Index in which the index key can have only one pointer value (row) associated with it
