Database Foreign Key and Relation Schema
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What is a foreign key?

  • An attribute in one table that links to a primary key in another table (correct)
  • An attribute that cannot be null
  • A primary key of a relation used in the same table
  • A unique identifier for each row in a table

    • In a binary relationship where the entity on the 'one side' is designated as the parent, which statement is true?

  • The relationship must be many-to-many.
  • The parent entity has many child entities. (correct)
  • The child entity can exist independently of the parent entity.
  • The parent entity is merged with the child entity.

    • A relation can contain duplicate tuples if it is well-structured.

    False

    What does a relation schema represent?

    <p>The name of the relation with its attributes.</p> Signup and view all the answers

    It is possible to merge three tables into one when both entities participate partially in a relationship.

    <p>False</p> Signup and view all the answers

    What do you call the primary key copy of one entity that appears as a foreign key in the relationship table?

    <p>Foreign key</p> Signup and view all the answers

    A foreign key references the primary key of another ________.

    <p>table</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Foreign Key = Links two tables by referencing a primary key Relation Instance = A finite set of tuples in a relation Well-Structured Relation = Contains minimal redundancy and logical attributes Relation Schema = Describes the name and attributes of a relation</p> Signup and view all the answers

    In a many-to-one relationship, the parent entity is located on the ______ side.

    <p>one</p> Signup and view all the answers

    Match the entities with their respective roles in a binary relationship:

    <p>Parent Entity = One side of relationship Child Entity = Many side of relationship Foreign Key = Link to parent entity Primary Key = Unique identifier for each record</p> Signup and view all the answers

    Which of the following is NOT a property of a table/relation?

    <p>Repeating groups are allowed</p> Signup and view all the answers

    The sequence of rows in a relation is insignificant.

    <p>True</p> Signup and view all the answers

    What is the requirement for a well-structured relation?

    <p>It should have minimal redundancy and allow operations without errors.</p> Signup and view all the answers

    What is the primary purpose of ER-to-Relations mapping?

    <p>To create relations for the logical data model</p> Signup and view all the answers

    In a relational schema, a strong entity is represented by a composite attribute.

    <p>False</p> Signup and view all the answers

    What attribute of an entity is generally set as the primary key in a relational schema?

    <p>Key attribute</p> Signup and view all the answers

    The entity set with __________ attributes must have its child attributes mapped as simple attributes in the relational schema.

    <p>Composite</p> Signup and view all the answers

    Match the type of attribute to its corresponding mapping in a relational schema:

    <p>Single-valued = Mapped as attributes in the relation Composite = Mapped as child attributes, parent is ignored Multi-valued = Requires a separate table for the multi-valued attribute Primary key = Uniquely identifies tuples in the relation</p> Signup and view all the answers

    Which of the following statements accurately describes how a strong entity set is mapped into a relational schema?

    <p>Single-valued attributes are represented directly as table attributes</p> Signup and view all the answers

    A composite attribute is represented in a relational schema by including the composite attribute itself.

    <p>False</p> Signup and view all the answers

    What happens to an entity occurrence in a relational schema?

    <p>It is represented by a tuple in the corresponding relation.</p> Signup and view all the answers

    What does the lossless-join property enable us to do?

    <p>Find any instance of the original relation from smaller relations</p> Signup and view all the answers

    The third normal form (3NF) is considered the highest level of normalization necessary for most applications.

    <p>True</p> Signup and view all the answers

    What is the key requirement for a table to be in First Normal Form (1NF)?

    <p>It should only have single (atomic) valued attributes.</p> Signup and view all the answers

    For a table to be in Second Normal Form (2NF), it must meet the requirements of First Normal Form and not have __________.

    <p>Partial Dependency</p> Signup and view all the answers

    Match the following normal forms with their descriptions:

    <p>First Normal Form = Single valued attributes Second Normal Form = No partial dependencies Third Normal Form = No transitive dependencies BCNF = Stronger than 3NF</p> Signup and view all the answers

    Which of the following is NOT a requirement for First Normal Form (1NF)?

    <p>Columns can contain multiple values</p> Signup and view all the answers

    An attribute is fully functional dependent on another if it is dependent on any part of the attribute.

    <p>False</p> Signup and view all the answers

    What is the primary goal of normalization in database design?

    <p>To eliminate redundancy and ensure data integrity.</p> Signup and view all the answers

    What is the main goal of the third normal form (3NF)?

    <p>To ensure referential integrity and eliminate redundancies</p> Signup and view all the answers

    A transitive dependency occurs when a non-prime attribute depends directly on a prime attribute.

    <p>False</p> Signup and view all the answers

    What should be done to remove a transitive dependency?

    <p>Divide the table and move the non-prime attribute to another table.</p> Signup and view all the answers

    In the context of BCNF, if a functional dependency is represented as A → B, then A must be a __________.

    <p>super key</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>3NF = A level of database normalization that eliminates transitive dependencies BCNF = A stricter version of 3NF that requires functional dependency constraints Transitive Dependency = When a non-prime attribute is dependent on another non-prime attribute Prime Attribute = An attribute that is part of a candidate key</p> Signup and view all the answers

    Which of the following is true about BCNF?

    <p>A table in BCNF must also satisfy all conditions of 3NF.</p> Signup and view all the answers

    In the example of the employee database, the table initially satisfies BCNF.

    <p>False</p> Signup and view all the answers

    What happens when a non-prime attribute depends on a prime attribute?

    <p>It does not create a transitive dependency.</p> Signup and view all the answers

    Study Notes

    Foreign Key

    • A foreign key is an attribute or set of attributes in one table that matches a primary key of another table, establishing a relationship.
    • It serves as a cross-reference between tables, linking data to maintain referential integrity.
    • A foreign key may not be unique and can appear multiple times in the referencing table.

    Relation Schema

    • A relation schema defines the structure of a database table, including its name and attributes, e.g., customer(customer_id, customer_name, customer_gender).
    • Relation instances consist of a finite set of unique tuples without duplicates.

    Well-Structured Relation

    • A well-structured relation has minimal redundancy and maintains logical coherence among attributes.
    • It permits efficient data insertion, modification, and deletion without inconsistencies.

    Properties of a Table/Relation

    • Each table has a unique name distinct from others in the database.
    • There are no duplicate rows, ensuring uniqueness for every entry.
    • Tables do not have repeating groups or multivalued attributes.
    • Each column consists of entries from the same domain based on its data type, including numeric, string, date, and logical values.
    • Operations between different data types are not allowed, and each attribute must have a unique name.

    Transforming E-R Diagrams into Relational Models

    • ER diagrams are transformed into relational models for implementation in RDBMS.
    • Steps in this transformation include representing entities, relationships, normalizing relations, and merging relations.
    • The mapping process specifies the schema, primary keys, and any foreign key references.

    Strong Entity Set Representation

    • Strong entities are mapped as tables with single-valued attributes turned into table attributes.
    • Key attributes become primary keys in the relational schema.

    Composite Attribute Handling

    • Composite attributes are converted with child components represented as simple attributes; parent attributes are ignored.
    • For example, customer_name may be broken down into customer_fname, customer_fathername, and customer_gfatherName.

    Multivalued Attribute Conversion

    • For entities with multivalued attributes, each entity and relationship is converted to separate tables.
    • Relationships are managed to ensure primary keys reference foreign keys appropriately.

    Binary Relationship Handling

    • In M:1 or 1:M relationships, the 'one' side is the parent entity, and the 'many' side is the child entity.
    • After creating tables for both entities, the child's table receives a foreign key reference to the parent's primary key.

    Normalization Forms

    • Normalization is a process aimed at minimizing redundancy and preserving data integrity within relations.
    • Normal forms include: First Normal Form (1NF), Second Normal Form (2NF), Third Normal Form (3NF), Boyce-Codd Normal Form (BCNF), and Fourth Normal Form (4NF).

    First Normal Form (1NF)

    • Achieved when all attributes contain single, atomic values and each column has unique names.
    • Values in each column must originate from the same domain, with no changes to the attribute domain over time.

    Second Normal Form (2NF)

    • Requires that the table is in 1NF and devoid of partial dependencies.
    • Full functional dependency must exist, meaning no non-key attributes depend on only part of a composite key.

    Third Normal Form (3NF)

    • Composed of two conditions: the table must be in 2NF and free of transitive dependencies.
    • Any non-prime attribute must not depend on other non-prime attributes to promote referential integrity.

    Boyce-Codd Normal Form (BCNF)

    • A stricter version of 3NF that addresses anomalies where multiple candidate keys exist.
    • A table is in BCNF if, for every functional dependency, the determinant must be a super key.

    Example of BCNF Violation

    • In a table with employee data, dependencies such as EMP_ID → EMP_COUNTRY and EMP_DEPT → {DEPT_TYPE, EMP_DEPT_NO} illustrate that neither EMP_ID nor EMP_DEPT alone are keys, violating BCNF.

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    Description

    This quiz explores the concepts of foreign keys, relation schemas, and well-structured relations in databases. Understand how these elements work together to maintain referential integrity and ensure efficient data management. Test your knowledge on properties of tables and relations to enhance your database skills.

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