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Mobiprep has created last-minute notes for all topics of Relational Model to help you with the revision of concepts for your university examinations. So let’s get started with the lecture notes on Relational Model.
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Relational Model
Question 1 - Explain various anomalies in Relation Model.
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Question 2 - Explain insertion, deletion and updation anomalies in Relational Database.
Answer
Insertion anomaly - Insertion of a tuple is not possible in the referencing relation if the referencing attribute of the tuple is not present in the referenced relation. This is called an insertion anomaly.
Deletion anomaly - Deletion anomaly occurs in the referenced relation. A tuple in the referenced relation cannot be deleted if the referencing attribute is used by the referencing relation. This is called deletion anomaly.
Updation anomaly - Updation anomaly occurs in the referenced relation. A tuple in the referenced relation cannot be updated if the referencing attribute is used by the referencing relation. This is called updation anomaly.
Question 3 - What do you understand by Referential integrity?
Answer - Referential integrity is used to establish relationships between tables in a relational database. The primary key and the foreign key are used to maintain referential integrity between the tables. Referential integrity is achieved by the following two constraints:
The addition of any row in the referencing table can be done only if the corresponding primary key is present in the referenced relation.
The deletion of any row in the referenced table can be done only if all the records with the corresponding foreign key in the referencing relation are deleted.
Question 4 - Define Relational Database.
Answer - A relational database is a type of database that stores it’s data in the form of tables that are related to one another. Each table in the relational database is divided into rows and columns.
Question 5 - Explain Relational Database Management System in detail.
Answer - A Relational Database Management System is a software system that is used to manage the relational database. It helps us to access the database using queries. It allows us to execute SQL queries to perform insertion, deletion, and updation operations on the relational database.
Examples: MySQL, Oracle etc.,
Question 6 - What are the advantages of using relational database?
Answer - The following are the advantages of using a relational database:
A relational database consists of data in the form of tables that are easy to interpret.
Insertion, deletion, and updation operations can be performed easily.
Redundant data can be removed easily.
The implementation cost is less.
Availability of standard design tools to implement a relational database.
Join operations can be performed easily.
Question 7 - What are the Codd rules for a relational database?
Answer -
Foundation Rule: The RDBMS must be capable of managing the entire database.
Information Rule: Data stored must be a value of some cell in the table.
Guaranteed Access Rule: Every data element must be accessible by the table name, its primary key, and the name of the attribute whose value to be determined.
Systematic Treatment of NULL: NULL values must only correspond to missing, unknown, or not applicable values.
Active Online Catalog: The database schema must be stored in an online catalog, so that the authorized users can view the structure of the database.
Comprehensive Data Sub-language Rule: The database must be accessible by a language.
View Updating Rule: Views created for various purposes must be automatically updatable to the system.
High-level insert, update and delete rule: The database should support insert, delete, update operations. The database should also support set operations like union, intersection, and minus.
Physical data independence: The conceptual or external view of data must not be affected by changes in the physical location of the tables and their indexes.
Logical data independence: Addition or deletion of attributes of a relation must not affect the user’s view of the table.
Integrity independence: Modification of integrity constraints should not enforce modification at the application level.
Distribution independence: Data distribution over various locations should not be visible to end-users.
Non-Subversion Rule: Integrity rules should not be subverted or bypassed by low-level access.
Question 8 - What are the constraints in relational database model?
Answer -
1. Domain constraints
The attributes in the table must be of the specified data type
Multi-valued attributes should not be present in the database. All the values in the database must be atomic.
2. Key constraints
Every tuple in a relation must be unique.
The primary key cannot take a NULL value
3. Referential integrity constraints
The addition of any row in the referencing table can be done only if the corresponding primary key is present in the referenced relation.
The deletion of any row in the referenced table can be done only if all the records with the corresponding foreign key in the referencing relation are deleted.
4. Entity integrity constraints
All the primary key values must be unique. The primary key value must be NULL.
Question 9 - Define Attribute and Tuple in relational database.
Attribute: A column in a relation is called an attribute. The attributes define the properties all the items in the table.
Tuple: The rows or records in a table are called tuples. The tuples are characterized by the attributes.
Question 10 - Define Cardinality and Degree of a relational database.
Cardinality: Cardinality of a relation is the number of rows or tuples in that relation.
Degree: Degree of a relation refers to the number of columns or attributes in that relation.
Question 11 - Define Primary key.
Answer - A primary key of a relational database is the minimal group of attributes (columns) that identify each row in a table uniquely. A relation cannot have more than one primary key. The value of the primary key of a tuple cannot be NULL. Modification of the primary key value is not permitted.
Question 12 - Define Foreign key.
Answer - The foreign key is used to define the relationship between two tables. The foreign key of one table refers to the primary key of another table. The foreign key is used to maintain data integrity between two tables in a relation.
Question 13 - Define Candidate key.
Answer - The candidate key is the set of all attributes in a relation that identify each tuple uniquely. The candidate key cannot have any redundant attributes. Only one among the candidate keys is chosen as the primary key.
Question 14 - Define Super key.
Answer - A super key is the set of attributes which can uniquely define each tuple in a relation. A relation can have one or more super keys.
Question 15 - What is an Alternate key?
Answer - A table has more than one minimal set of attributes that can uniquely define a tuple (candidate keys). But, only one among them is chosen as the primary key. The candidate keys other than the primary key are called alternate keys.
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