Podcast
Questions and Answers
What is the correct terminology for the components of a relation?
What is the correct terminology for the components of a relation?
- Entity, instance, value
- Table, row, column
- Relation, tuple, attribute (correct)
- Set, element, property
What is a key characteristic of a relation in a database?
What is a key characteristic of a relation in a database?
- Tuples are distinct; there are no duplicates (correct)
- The order of attributes has significance
- Tuples can have duplicate values
- Attributes can have duplicate names
What is a super key in the context of database systems?
What is a super key in the context of database systems?
- A set of attributes that uniquely identifies a tuple within a relation (correct)
- The primary key of a relation
- An attribute that uniquely identifies a relation
- A foreign key referencing another relation
What is true about a candidate key in a database system?
What is true about a candidate key in a database system?
What is a composite key in a database system?
What is a composite key in a database system?
What does a foreign key represent in a database system?
What does a foreign key represent in a database system?
What does the entity integrity constraint state in a database system?
What does the entity integrity constraint state in a database system?
What is a base relation in a database system?
What is a base relation in a database system?
What represents a physically stored relation in the database?
What represents a physically stored relation in the database?
What is represented by an entity type in the ER model?
What is represented by an entity type in the ER model?
What is a relationship type in the ER model?
What is a relationship type in the ER model?
What is an attribute in the ER model?
What is an attribute in the ER model?
What is the difference between a composite attribute and a simple attribute?
What is the difference between a composite attribute and a simple attribute?
What is a multivalued attribute?
What is a multivalued attribute?
What is a derived attribute?
What is a derived attribute?
What does a value set or domain represent for an attribute?
What does a value set or domain represent for an attribute?
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Study Notes
Database Systems: Components and Terminology
- A relation consists of tuples (rows) and attributes (columns)
- Correct terminology: relation, tuple, attribute
- Attributes can have distinct names, but no duplicates
Properties of Relations
- Each cell contains exactly one atomic value
- Tuples are distinct, no duplicates
- The order of attributes has no significance
Keys
- A super key is a set of attributes that uniquely identifies a tuple within a relation
- A candidate key is a super key with no proper subset being a super key
- A primary key is a selected candidate key for each relation
- A composite key consists of more than one attribute
Foreign Keys
- A foreign key represents an attribute that matches the primary key of another relation
- Foreign keys must match a candidate key value or be null
Entity Integrity Constraint
- No attribute of a primary key can be null
Base Relations and Views
- A base relation is a named relation stored in the database
- A view is a dynamic result of relational operations on base relations
ER Model: Entity Types, Relationships, and Attributes
- An entity type represents a group of objects with the same properties
- A relationship type represents a set of meaningful associations among entity types
- An attribute is a property of an entity or a relationship type
Attributes in ER Model
- A composite attribute can be divided into smaller subparts
- A multivalued attribute can have multiple values for each entity
- A derived attribute is calculated from other attributes
- A value set or domain represents the set of all possible values for an attribute
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