Data Modeling - entity-relationship diagrams, relational model, constraints, relational algebra, relational calculus, Codd rules - One Line Questions
1.
In the relational model, what is a 'tuple'? —
A row in a relation.
2.
The Join operation (⋈) in relational algebra combines tuples from two relations based on: —
A condition on attributes.
3.
What is the relational model? —
A data model based on tables (relations) consisting of rows and columns.
4.
What is a 'foreign key' in the relational model? —
A set of attributes in one relation that refers to the primary key of another relation.
5.
The concept of a 'relation' in the relational model is formally defined as: —
A set of tuples.
6.
An oval shape connected to an entity or relationship in an ERD represents: —
An attribute
7.
What is the fundamental difference between a PRIMARY KEY and a UNIQUE constraint? —
A UNIQUE constraint can contain NULL values, while a PRIMARY KEY cannot.
8.
What is Relational Algebra? —
A procedural query language for the relational model.
9.
What is Relational Calculus? —
A declarative query language for the relational model.
10.
What is an 'attribute' in the relational model? —
A column in a relation.
11.
What is a 'primary key' in a relational table? —
A set of attributes that uniquely identifies a tuple and cannot be null.
12.
In Tuple Relational Calculus, a query is expressed as: —
A set of tuples satisfying certain conditions.
13.
According to Codd's rules, what must be supported for handling missing or inapplicable information? —
A systematic treatment of NULL values.
14.
What does the 'NOT NULL' constraint enforce on a column? —
The column cannot contain NULL values.
15.
Codd's Rule 6, the 'View Update Rule', states that: —
The system must support the modification of data through views.
16.
In an ERD, what does a rectangle typically represent? —
An entity set.
17.
What does a diamond shape represent in an ERD? —
A relationship
18.
What is a 'weak entity' in the context of ER diagrams? —
An entity that cannot be uniquely identified by its own attributes and requires a foreign key from another entity.
19.
What is the term for the number of attributes in a relation? —
Arity
20.
What is the term for the number of tuples in a relation? —
Cardinality
21.
Codd's Rule 9, 'Logical Data Independence', ensures that: —
Changes to the overall database schema do not affect applications.
22.
The Union operation (∪) in relational algebra requires that the two relations have: —
Compatible schemas (same number of attributes and compatible types).
23.
Which type of relational calculus focuses on specifying the variables that tuples must range over? —
Tuple Relational Calculus
24.
What is the primary advantage of using a declarative query language like SQL (which is based on relational calculus) over a procedural one like relational algebra? —
Better performance optimization by the DBMS.
25.
A CHECK constraint is used to: —
Ensure that values in a column satisfy a specified condition.
26.
Codd's Rule 2, the 'Guaranteed Access Rule', states that: —
Every distinct piece of data must be addressable using a primary key.
27.
Which constraint ensures that the values in a specific column are unique across all rows? —
UNIQUE constraint
28.
Which type of relationship in an ERD indicates that each instance of an entity can be associated with at most one instance of another entity? —
One-to-One (1:1)
29.
Codd's Rule 4 emphasizes the importance of: —
A dynamic and online data dictionary or catalog.
30.
Which relational algebra operator is used to select rows from a relation based on a condition? —
Select (σ)
31.
Which of Codd's rules states that the database must be logically representable and accessible through the relational model alone? —
Rule 1: Information Rule
32.
Which of Codd's rules implies that the database should not contain any 'foreign keys' in the traditional sense, but rather rely on relational algebra operations for relating tables? —
Rule 2: Guaranteed Access Rule
33.
Which of Codd's rules is often considered the most important for enforcing the relational model's integrity? —
Rule 2: Guaranteed Access Rule
34.
Which of Codd's rules is fundamental to the concept of relational algebra and calculus, stating that data manipulation must be supported by a high-level language? —
Rule 5: Comprehensive Data Sublanguage
35.
Which of the following is NOT a standard operator in Relational Algebra? —
Aggregate
36.
Which relational algebra operator is used to select columns from a relation? —
Project (π)
37.
Which relational algebra operator corresponds to the SQL `SELECT` statement that specifies columns? —
Project (π)
38.
Which relational algebra operator corresponds to the SQL `WHERE` clause? —
Select (σ)
39.
Which relational algebra operator is used to remove duplicate tuples from a relation? —
Union (∪)
40.
Codd's 12 Rules are a set of criteria for evaluating: —
The quality and functionality of relational database management systems (RDBMS).
41.
A 'participation constraint' in an ERD specifies: —
The minimum number of instances an entity must participate in a relationship.
42.
In the context of ER diagrams, a 'cardinality ratio' defines: —
The maximum and minimum number of instances of one entity that can be related to instances of another entity.
43.
What is the relationship between Relational Algebra and Relational Calculus? —
They are equivalent in expressive power; any query expressible in one can be expressed in the other.
44.
What is the primary purpose of an Entity-Relationship Diagram (ERD)? —
To represent the logical structure of a database and the relationships between entities.
45.
What is the purpose of the 'non-subversion' rule (Rule 12) in Codd's 12 rules? —
To ensure that the system cannot be used to bypass security.
46.
Which type of relational calculus focuses on specifying the domains (possible values) that attributes must take? —
Domain Relational Calculus
47.
What does Codd's Rule 8, 'Physical Data Independence', ensure? —
Application programs remain unaffected by changes in physical storage structures.
48.
What is the symbol for the Select operation in relational algebra? —
σ
49.
What is the symbol for the Project operation in relational algebra? —
π