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Questions and Answers
What are descriptive attributes used for?
What are descriptive attributes used for?
Record information about the relationship
Each relationship must be uniquely identified by the participating entities and descriptive attributes.
Each relationship must be uniquely identified by the participating entities and descriptive attributes.
False
Which type of relationship involves two entities in the same entity set?
Which type of relationship involves two entities in the same entity set?
Can an employee work in two locations for the same department? Yes/No. This is an example of ________ relationship.
Can an employee work in two locations for the same department? Yes/No. This is an example of ________ relationship.
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Match the key constraint with its description:
Match the key constraint with its description:
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What does total participation in a relationship mean?
What does total participation in a relationship mean?
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What does partial participation in a relationship mean?
What does partial participation in a relationship mean?
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What is a weak entity?
What is a weak entity?
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Attributes are inherited by subclasses in a class hierarchy.
Attributes are inherited by subclasses in a class hierarchy.
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What is the purpose of the Entity-Relationship (ER) model in database design?
What is the purpose of the Entity-Relationship (ER) model in database design?
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What is an entity in the Entity-Relationship model?
What is an entity in the Entity-Relationship model?
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An entity set is a collection of entities of the same ______.
An entity set is a collection of entities of the same ______.
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Entities in a given entity set have the same attributes with the same values.
Entities in a given entity set have the same attributes with the same values.
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What is a candidate key in database design?
What is a candidate key in database design?
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Match the following components of the ER model with their descriptions:
Match the following components of the ER model with their descriptions:
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Study Notes
Database Design and Administration
- The database design process consists of six steps:
- Requirement Analysis
- Conceptual Database Design (ER)
- Logical Database Design (Relational)
- Schema Refinement
- Physical Database Design
- Application and Security Design
Entity-Relationship Model
- The Entity-Relationship (ER) model is a popular conceptual data model used in database design.
- It describes the data to be stored and the constraints over the data.
Entities and Attributes
- An entity is an object in the real world that is distinguishable from other objects.
- An entity is described using a set of attributes whose values are used to distinguish one entity from another of the same type.
- An entity set is a collection of entities of the same type.
- All entities in a given entity set have the same attributes, but the values may differ.
- Attribute domain refers to the set of possible values for an attribute.
ER Diagrams
- ER diagrams can be used to present the ER model graphically.
Key
- A candidate key is a minimal set of attributes whose values uniquely identify an entity in the set.
- There can be more than one candidate key.
- The primary key should be chosen based on real-life possibilities rather than the current set of data.
Relationships
- A relationship is an association among two or more entities.
- A relationship can be represented by an ER diagram.
- A relationship set can be seen as a set of n-tuples.
Ternary Relationships
- A ternary relationship is a relationship between three entities.
- It can be represented by an ER diagram.
Recursive Relationships
- A recursive relationship is a relationship between two entities in the same entity set.
Key Constraints (Mapping Constraints)
- The mapping of a binary relationship can be classified into four cases:
- One-to-one
- One-to-many
- Many-to-one
- Many-to-many
One-to-One Relationship
- In a one-to-one relationship, an entity in A is related to at most one entity in B, and an entity in B is related to at most one entity in A.
One-to-Many Relationship
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In a one-to-many relationship, an entity in B can be associated with at most one entity in A, and an entity in A can be associated with one or more than one entity in B.### Key Constraints
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A child has a key constraint in a mother-of relationship set, indicated by an arrow in the E-R diagram.
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Intuitively, the arrow means that given a child entity, we can uniquely determine the mother-of relationship.
One-to-Many (1:N)
- In a one-to-many relationship, an entity in A is associated with one or more entities in B.
- Example: a mother has multiple children, but a child has only one mother.
Many-to-One (N:1)
- Similar to one-to-many, but an entity in A is associated with one entity in B.
- Example: an employee works in one department, but a department can have multiple employees.
Many-to-Many (M:N)
- An entity in A is associated with any number of entities in B, and an entity in B is associated with any number of entities in A.
- No restriction in the mapping, e.g., a customer can have multiple loans, and a loan can be associated with multiple customers.
Participation Constraint
- Imposes requirements on whether an entity participates in a relationship.
- Total Participation: each entity in the entity set must participate in at least one relationship.
- Partial Participation: an entity in the entity set may not participate in a relationship.
Participation Constraint Examples
- Every department is required to have a manager (total participation).
- Every employee must work for some department (total participation).
- Some employees may not manage departments (partial participation).
Entities
- There are two kinds of entities: strong and weak.
- Strong entity: has a primary key and can be distinguished from other entities in the same set.
- Weak entity: lacks a primary key and may not be distinguished from others without associations with entities in other sets.
Weak Entity Example
- Dependent entity set: lacks a primary key, and pname does not identify a dependent uniquely.
- The primary key of the employee (identifying owner) is required to identify a dependent entity.
- A partial key is a set of attributes that uniquely identify a weak entity for a given owner entity.
Class Hierarchies
- Allow classification of entities in an entity set into subclasses.
- Attributes are inherited by the entity set in the subclass.
- A class hierarchy can be viewed as a specialization or generalization.
- Two kinds of constraints can be specified with respect to ISA hierarchies: overlap constraints and covering constraints.
ISA Hierarchies Constraints
- Overlap constraints: determine whether two subclasses are allowed to contain the same entity.
- Covering constraints: determine whether the entities in the subclasses collectively include all entities in the superclass.
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Description
This quiz covers the basics of database design and administration, focusing on the Entity-Relationship Model, entities, attributes, keys, relationships, and advanced concepts like ternary and recursive relationships.
