MCQs~Databases~Relational Model and Normalization

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1 Database normalization is the process of organizing the fields and tables of a relational database to minimize redundancy. Normalization usually involves dividing large tables into smaller (and less redundant) tables and defining relationships between them. The objective is to isolate data so that additions, deletions, and modifications of a field can be made in just one table and then propagated through the rest of the database using the defined relationships. Edgar F. Codd, the inventor of the relational model, introduced the concept of normalization and what we now know as the First Normal Form (1NF) in 1970.[1] Codd went on to define the Second Normal Form (2NF) and Third Normal Form (3NF) in 1971,[2] and Codd and Raymond F. Boyce defined the Boyce-Codd Normal Form (BCNF) in 1974.[3] Informally, a relational database table is often described as "normalized" if it is in the Third Normal Form.[4] Most 3NF tables are free of insertion, update, and deletion anomalies. A standard piece of database design guidance is that the designer should first create a fully normalized design; then selective denormalization can be performed for performance reasons.[5] A typical example of normalization is that a unique ID is stored everywhere in the system but its name is held in only one table. The name can be updated more easily in one row of one table. A typical update in such an example would be the RIM company changing its name to BlackBerry.[6] That update would be done in one place and immediately the correct "BlackBerry" name would be displayed throughout the system. 1. Every time attribute A appears, it is matched with the same value of attribute B, but not the same value of attribute C. Therefore, it is true that: A. A? B. B. A? C. C. A? (B,C). D. (B,C)? A. 2. The different classes of relations created by the technique for preventing modification anomalies are called: A. normal forms. B. referential integrity constraints. C. functional dependencies. D. None of the above is correct. 3. Page 1

2 A relation is in this form if it is in BCNF and has no multivalued dependencies: A. second normal form. B. third normal form. C. fourth normal form. D. domain/key normal form. 4. Row is synonymous with the term: A. record. B. relation. C. column. D. field. 5. The primary key is selected from the: A. composite keys. B. determinants. C. candidate keys. D. foreign keys. 6. Which of the following is a group of one or more attributes that uniquely identifies a row? A. Key B. Determinant C. Tuple D. Relation 7. When the values in one or more attributes being used as a foreign key must exist in another set of one or more attributes in another table, we have created a(n): A. transitive dependency. B. insertion anomaly. C. referential integrity constraint. D. normal form. 8. Page 2

3 A relation is considered a: A. Column. B. one-dimensional table. C. two-dimensional table. D. three-dimensional table. 9. In the relational model, relationships between relations or tables are created by using: A. composite keys. B. determinants. C. candidate keys. D. foreign keys. Answer: Option D 10. A functional dependency is a relationship between or among: A. tables. B. rows. C. relations. D. attributes. Answer: Option D 11. Table is synonymous with the term: A. record. B. relation. C. column. D. field. Answer: Option B 12. Which of the following is not a restriction for a table to be a relation? A. The cells of the table must contain a single value. B. All of the entries in any column must be of the same kind. C. The columns must be ordered. D. No two rows in a table may be identical. Explanation: (A) The cells may or may not contian values (NOT NULL or NULL) Page 3

4 (B) is strict to enforce and varies across databases (C) Columns can be in any order, it does not affect the table structure/the relation (D) Can be identical for all non-unique fields (columns) 13. For some relations, changing the data can have undesirable consequences called: A. referential integrity constraints. B. modification anomalies. C. normal forms. D. transitive dependencies. Answer: Option B Explanation: (You can find a nice discussion here: There are Three types of MODIFICATION ANOMALIES Insertion Anomaly: failure to place information a new database entry in all the places in the database where information about a new entry needs to be stored. Deletion Anomaly: failure to remove information about an existing database entry when it is time to remove that entry. Update Anomaly: update of a database involves modifications that may be additions, deletions, or both. Thus "update anomalies" can be either insertion or deletion anomaly. "These problems with the addition and deletion of data, normal everyday stuff, have to be considered when designing, decomposing relations into new relations, determining primary keys, foreign keys, and the like. As can be seen by these examples disaster can strike, if we fail to properly normalize our data." 14. A key: A. must always be composed of two or more columns. B. can only be one column. C. identifies a row. D. identifies a column. 15. An attribute is a(n): A. column of a table. B. two dimensional table. Page 4

5 C. row of a table. D. key of a table. 16. A relation in this form is free of all modification anomalies. A. First normal form B. Second normal form C. Third normal form D. Domain/key normal form Answer: Option D 17. If attributes A and B determine attribute C, then it is also true that: A. A --> C. B. B --> C. C. (A,B) is a composite determinant. D. C is a determinant. 18. A tuple is a(n): A. column of a table. B. two dimensional table. C. row of a table. D. key of a table. 19. If attribute A determines both attributes B and C, then it is also true that: A. A --> B. B. B --> A. C. C --> A. D. (B,C) --> A. 20. Page 5

6 One solution to the multivalued dependency constraint problem is to: A. split the relation into two relations, each with a single theme. B. change the theme. C. create a new theme. D. add a composite key. Explanation: ( Consider this example of a database of teaching courses, the books recommended for the course, and the lecturers who will be teaching the course: Course Book Lecturer AHA Silberschatz John D AHA Nederpelt William M AHA Silberschatz William M AHA Nederpelt John D AHA Silberschatz Christian G AHA Nederpelt Christian G OSO Silberschatz John D OSO Silberschatz William M Because the lecturers attached to the course and the books attached to the course are independent of each other, this database design has a multivalued dependency; if we were to add a new book to the AHA course, we would have to add one record for each of the lecturers on that course, and vice versa. Put formally, there are two multivalued dependencies in this relation: {course} -->> {book} and equivalently {course} -->> {lecturer}. Databases with multivalued dependencies thus exhibit redundancy. In database normalization, fourth normal form requires that either every multivalued dependency X -->> Y is trivial or for every nontrivial multivalued dependency X -->> Y, X is a superkey. Page 6

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