Final - DB design Flashcards
What is the first phase of database design?
Characterize users’ data needs
This includes identifying who the users are and how to characterize their data needs.
What is the purpose of choosing a data modeling technique?
To select an appropriate method for representing data, such as relational model or E-R model.
What is a conceptual schema?
A representation that captures the users’ data needs, often designed by a data modeling team.
What is typically used to design a conceptual schema?
The E-R model.
What is the purpose of reviewing the schema?
To ensure it supports all functional requirements and that data required for all outputs is present.
What does mapping the conceptual model to a logical model involve?
Translating the conceptual schema into a logical structure that can be implemented in a database.
What is the E-R model?
A data model used in database design that maps meanings and interactions of real-world entities onto the conceptual schema.
Define ‘Entity’ in the context of E-R models.
An object that exists and is distinguishable from other objects.
What is an ‘Entity Set’?
A set of entities of the same type that share the same properties.
What is a ‘Relationship’ in E-R models?
An association among several entities.
Define ‘Relationship Set’.
A mathematical relation among n ≥ 2 entities.
List the entities of the Library example.
- Libraries
- Books
- Authors
What are ‘Attributes’ in the context of an entity set?
Properties possessed by all members of an entity set.
What is a ‘Domain’?
A set of permitted values for each attribute.
Define ‘Composite Attributes’.
Attributes that can be divided into other attributes.
Give an example of a composite attribute.
Address can be divided into street, city, state, postal_code.
What differentiates Single vs Multivalued Attributes?
Single has a single value; multivalued has a set of values for a specific entity set.
What is a ‘Derived Attribute’?
An attribute that can be computed from other attributes.
List the attributes of the library entities.
- Library: (ID, name, address, …)
- Book: (Title, publisher, ISBN, genre, …)
- Author: (ID, name, …)
What are ‘Cardinalities’ in E-R models?
They express the number of entities to which another entity can be associated.
Define ‘One-to-One’ cardinality.
An entity in A is associated with AT MOST one entity in B, and vice versa.
Define ‘One-to-Many’ cardinality.
An entity in A is associated with 0 or more entities in B, but an entity in B can be associated with AT MOST one entity in A.
Define ‘Many-to-Many’ cardinality.
An entity in A is associated with 0 or more entities in B, and vice versa.
What does an E-R diagram express?
The logical structure of a database graph.
What do divided rectangles in E-R diagrams represent?
Entity sets.
What do diamonds represent in E-R diagrams?
Relationship sets.
What do solid lines indicate in E-R diagrams?
Links between entity sets and relationship sets.
What do undivided rectangles represent in E-R diagrams?
Descriptive attributes of a relationship set.
What do dashed lines indicate in E-R diagrams?
Links between descriptive attributes and the relationship set.
What do double lines denote in E-R diagrams?
Total participation; every entity participates in at least one relationship.
What do double diamonds indicate?
An identifying relationship between a strong and weak entity set.
What is a strong entity set?
An entity set that has a primary key (PK).
What is a weak entity set?
An entity set that has no primary key (PK), so its PK is formed by the PK of the identifying entity set plus the weak entity set.
