Question

, Univ Section«, InstructorName, Semester, BuildingCode, Roome, TimePeriod, Weekdays, CreditHours). This represents classes taught in … # Consider the relation CLASs(Course#, Univ Section«, InstructorName, Semester, BuildingCode, Roome, TimePeriod, Weekdays, CreditHours). This represents classes taught in a university, with unique Univ_Section#. Identify what you think should be various candidate keys, and write in your own words the constraints under which each candidate key would be valid.

Short answer

The candidate keys could be Univ_Section# and the composite key (Course#, InstructorName, Semester, TimePeriod). For Univ_Section#, the constraint is it should be unique for each class. For the composite key, the constraint is an instructor cannot teach the same course at the same time in the same semester.

Step-by-step solution

Understanding the Relation

The given relation is CLASS with attributes Course#, Univ Section#, InstructorName, Semester, BuildingCode, Room#, TimePeriod, Weekdays, CreditHours. The unique identifier mentioned is Univ_Section#. The other attributes do not have unique constraints directly mentioned.

Identifying Candidate Keys

A good candidate key would be Univ_Section# as per the question. Another plausible candidate key could be a composite key of (Course#, InstructorName, Semester, TimePeriod), assuming a teacher does not teach the same course in the same semester at the same time.

Defining Constraints

The constraints under which the above keys would be valid are: For Univ_Section#, the constraint is that it should be unique for each class. For the composite key (Course#, InstructorName, Semester, TimePeriod), the constraint is that an instructor cannot teach the same course at the same time in the same semester.

Key concepts

Relational Databases

To understand the underpinnings of candidate keys, a fundamental grasp on what a relational database is becomes essential. A relational database is a type of database that stores and provides access to data points that are related to one another. These databases are structured to recognize relations among stored items of information. For example, in a university database, different relations (or tables) could be established for students, classes, and faculty.

Each table within a relational database is a collection of data items organized in a set of formally-described columns. In our exercise example, the relation (or table) named CLASS has columns like InstructorName, Semester, and BuildingCode, that all bear some relation to the concept of a university course.

Importance of Cleanness and Accuracy

In terms of maintenance and retrieval of data, relational databases must prioritize the accuracy and cleanness of data. Even a small error or redundancy can lead to substantial complications across the complex web of relationships. This is why identifying candidate keys, ensuring proper constraints, and employing methods like database normalization are vital steps in database design and management.

Database Normalization

Database normalization is the process of organizing a database in a way that reduces redundancy and dependency of data. It involves dividing large tables into smaller, more manageable pieces with relationships between them that give structure to the database.

In practice, normalization often involves multiple stages, referred to as 'normal forms', each with specific requirements and benefits.

Benefits of Normalization

The primary benefits are two-fold: it ensures data is logically stored (preventing anomalies during data operations), and it enhances data integrity. Consider our CLASS table - without adequate normalization, there could be multiple entries for the same class with slight variations, leading to confusion and errors. By identifying appropriate candidate keys and employing normalization techniques, a consistent and non-redundant representation of the data is maintained.

Primary Key Constraints

Within the realm of relational databases, the concept of primary key constraints is crucial. A primary key is a specific choice among the candidate keys available for a database table. The primary key must contain unique values, and it cannot contain null values.

In our textbook example, while the Univ_Section# could serve as a primary key due to its uniqueness, additional candidate keys were also considered.

Enforcing Uniqueness and Integrity

The primary key constraint enforce that each row in a table can be uniquely identified by the values in the primary key column(s), which is what makes the data retrieval efficient and reliable. This constraint provides the table with a reliable way to enforce the uniqueness of data, hence supporting the integrity of the dataset. It is critical that primary key constraints are planned carefully during the database design phase to avoid future complications and to maintain the structural integrity of the relations within the database.