Final answer:
Multi-valued fields are not allowed in relational databases due to the principle of the relational model that dictates each field should contain only one value per record. Instead, normalization and separate tables are used to handle multi-valued attributes.
Step-by-step explanation:
The question asks whether multi-valued fields are allowed in relational databases. The correct answer is that multi-valued fields are not allowed in relational databases.
This is because the relational model is based on the concept that each field (also known as attribute or column) within a table should contain only one value per record (or tuple). This principle is part of the rules defined by the database normalization process, which aims to reduce redundancy and improve data integrity.
In a case where multi-valued attributes are necessary, separate tables are created to handle the relationships, often with the use of foreign keys.
This helps to ensure each field contains a single value, maintaining the integrity of the relational structure. The process of dividing a table into more-related tables to store data separately is referred to as normalization. It can help avoid problems such as update anomalies, insert anomalies, and delete anomalies;
however, this might have an impact on the speed of retrieving and updating data, depending on the complexity of the database structure and the relationships between the tables.