The Relational Model Flashcards
What are the three components of a data model?
- Structural part
- Manipulative part
- Integrity rules
Integrity rules ensure that the stored data is accurate.
What is a Relational Model based on?
2D tables, set theory, and relational algebra.
What is a Relation in the context of a relational database?
A table with columns and rows.
What does the Degree of a relation refer to?
The number of attributes it contains.
What does Cardinality indicate in a relation?
The number of tuples contained in a relation.
Tuble = Row
What is an Attribute in a relation?
A named column.
Fill in the blank: A _______ is a row of a relation.
Tuple
What is a Domain in the context of a relational database?
The set of allowable values for one or more attributes.
What is a Superkey?
An attribute or set of attributes that uniquely identifies a tuple within a relation.
What is a Candidate Key?
A minimal superkey that uniquely identifies a tuple without redundant attributes.
True or False: A candidate key can only involve one attribute.
False
What are the two properties of candidate keys?
- Uniqueness
- Irreducibility
What is a Primary Key?
A candidate key selected to identify tuples uniquely within the relation.
What is an Alternate Key?
Candidate keys that are not selected to be the primary key.
Fill in the blank: Relational database schema is a collection of appropriately structured _______.
relations
What is the significance of the order of attributes and tuples in a relation?
The order has no significance.
What must each cell of a relation contain?
Exactly one single (atomic) value.
What does the term ‘tuple’ refer to in a relational database?
A row of a relation.
What is an alternate key?
A candidate key that is not selected to be the primary key.
What is a foreign key?
An attribute that establishes a relationship between two tables by linking to the primary key of another relation.
Can a foreign key have duplicate values?
Yes, a foreign key allows duplicate values in a relation.
What is relational integrity?
The set of integrity constraints that ensure the data in a relational database is accurate.
What are the two principal integrity rules?
- Entity integrity rule
- Referential integrity rule
What does a Null represent in a database?
A value for an attribute that is currently unknown or not applicable.
True or False: A Null is the same as zero or spaces.
False
What does entity integrity ensure about primary key attributes?
Primary key attributes must be unique and not null.
What happens if a primary key value is duplicated?
Saving the record will give an error.
What is referential integrity?
It ensures the validity of foreign keys and consistency between linked tables.
What must a foreign key value do to maintain referential integrity?
It must match a candidate key value of some tuple in its home relation or be wholly null.
What issues can arise with entity integrity in a table?
Duplicate primary key values or NULL primary key values.
Fill in the blank: A _______ represents the absence of a value.
Null
Fill in the blank: The _______ ensures that no duplicate primary key values are allowed in a table.
Entity integrity
What is a relation?
A table
What is a relation schema?
It defined
What is relation schema?
A relation defined by a set of attributes and domain name pairs
What does referential integrity ensure?
That foreign keys are valid and consistency between linked tables
