Data modeling: ER diagrams, relational model, relational algebra and calculus, constraints and Codd rules. - One Line Questions

1. In tuple relational calculus, a query is expressed as: — { T | P(T) } where T is a tuple and P(T) is a condition
2. In domain relational calculus, a query is expressed as: — { <x1, x2, ..., xn> | P(x1, x2, ..., xn) } where xi are domain variables and P is a condition
3. A NOT NULL constraint ensures that: — A column cannot have a NULL value
4. A UNIQUE constraint ensures that: — A column cannot have duplicate values (excluding NULLs)
5. What does a double oval represent in an ER diagram? — A multi-valued attribute
6. A CHECK constraint allows you to specify: — A condition that must be true for each row's values
7. Which symbol in an ER diagram is used to represent a relationship between entity types? — A diamond
8. Which of the following best describes the relational model? — Data organized into tables (relations)
9. What does a line connecting an entity type and a relationship type signify in an ER diagram? — A link between the entity and the relationship
10. The Cartesian Product operation (A × B) between two relations A and B results in: — A relation containing all possible combinations of tuples from A and B
11. In an Entity-Relationship (ER) diagram, what does a rectangle typically represent? — An entity type
12. In the context of ER diagrams, what does an oval shape usually represent? —
13. The primary key is: — A chosen candidate key to uniquely identify tuples
14. In the relational model, a row in a relation is called a: — Tuple
15. The Join operation (⋈) in relational algebra typically combines tuples from two relations based on: — Matching values in specified attributes
16. Codd's Rule 2 (Guaranteed Access Rule) states that every scalar value in the database must be addressable: — By a table name, column name, and primary key value
17. The set of permissible values for an attribute is called its: — Domain
18. The number of attributes in a relation is known as its: — Degree
19. The number of tuples in a relation is known as its: — Cardinality
20. Codd's Rule 10 (Logical Data Independence) ensures that: — Changes in the logical structure (e.g., adding columns) do not affect applications
21. A candidate key is a superkey that: — Has no proper subset that is also a superkey
22. The fundamental difference between relational algebra and relational calculus is that algebra is __________ while calculus is _________. — procedural, declarative
23. Which type of relational calculus uses tuple variables? — Tuple relational calculus
24. A weak entity type is an entity type that: — Cannot be uniquely identified by its own attributes
25. The relationship between a weak entity type and its owner strong entity type is called: — Identifying relationship
26. Codd's Rule 4 requires that the database description (catalog) must be stored: — In the same relational system, allowing relational operations on it
27. The difference operation (A − B) in relational algebra returns tuples that are: — In relation A but not in relation B
28. Which relational algebra operation combines tuples from two relations that have the same attribute names and compatible domains, and where the tuples are identical in the common attributes? — Union (∪)
29. According to Codd's Rule 3, null values should be supported to represent: — Missing information or inapplicable information
30. An attribute whose value can be computed from other attributes is known as: — Derived attribute
31. The PRIMARY KEY constraint enforces which two constraints by default? — UNIQUE and NOT NULL
32. Codd's Rule 7 (High-level Insert, Update and Delete) states that the system must support: — Insert, update, and delete operations that can be applied to one or more rows
33. Which relational algebra operation selects rows from a relation based on a condition? — Selection (σ)
34. Which Codd rule states that the database must be logically representable using only the relational model, not as a network or hierarchy? — Rule 1: Information Rule
35. Which Codd rule ensures that users can perform all data manipulation and definition operations through the relational model's high-level language? —
36. Which Codd rule is related to the ability to update views? — Rule 6: View updating rule
37. Which relational algebra operation selects columns from a relation? — Projection (π)
38. Which of the following is a type of attribute that can be broken down into smaller sub-parts? — Composite attribute
39. In an ER diagram, a weak entity type is typically represented by a: — Double rectangle
40. What does Codd's Rule 9 (Physical Data Independence) guarantee? — That changes in physical storage (e.g., file organization) do not affect application programs
41. A foreign key is an attribute or set of attributes in one relation that refers to: — The primary key of another relation
42. What is the primary purpose of an ER diagram? — To describe the logical structure of a database
43. What is the purpose of constraints in a relational database? — To enforce data integrity rules
44. Relational calculus is a procedural query language. — False
45. Codd's Rule 11 (Integrity Rule) ensures that integrity constraints must be stored in the relational catalog and enforced by the DBMS. — True
46. What is a column in a relation called in the relational model? — Attribute
47. Which type of relational calculus uses domain variables? — Domain relational calculus
48. A superkey is a set of attributes that: — Uniquely identifies a tuple
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