Database Concepts: Triggers and Keys
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Questions and Answers

Which of the following describes the highest level of data abstraction in a database?

  • View level (correct)
  • Physical level
  • Logical level
  • File level

    • What is one of the primary purposes of a Database Management System (DBMS)?

  • To prevent data backup
  • To enforce integrity constraints (correct)
  • To increase data redundancy
  • To allow unlimited user access

    • Which integrity rule states that a foreign key can either be NULL or match a primary key in another table?

  • Entity Integrity
  • User-defined Integrity
  • Domain Integrity
  • Referential Integrity (correct)

    • What is the term for the number of tuples present in a table at any given time?

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

    Which of the following is a disadvantage of a file processing system?

    <p>Data isolation</p> Signup and view all the answers

    What is the purpose of a foreign key in a relational database?

    <p>To link two tables by referencing tuples in another table</p> Signup and view all the answers

    Which of the following best describes a cursor in PL/SQL?

    <p>A mechanism for iterating through a set of rows returned by a SQL statement</p> Signup and view all the answers

    What is a candidate key in the context of a database?

    <p>A minimal super key that can uniquely identify tuples in a relational table</p> Signup and view all the answers

    What characterizes Boyce-Codd Normal Form (BCNF) in a database normalization process?

    <p>Every functional dependency has a determinant that is a super key</p> Signup and view all the answers

    In terms of functional dependency, what does it signify when we say 'A determines B'?

    <p>If A is known, there is exactly one value of B that corresponds to it</p> Signup and view all the answers

    Study Notes

    Database Triggers

    • Triggers execute either once per statement or once per row that is inserted, updated, or deleted.
    • There are twelve events for which triggers can be defined for a single table
    • Triggers can call database procedures written in PL/SQL.

    Stored Procedures

    • Stored procedures are database objects that perform user-defined tasks.
    • They contain a set of compound SQL statements.
    • Stored procedures execute SQL commands and return results to clients.
    • They are used to reduce network traffic.

    Super Key

    • A super key is a set of one or more attributes that collectively identify a unique entity in an entity set.
    • Example: {SSN} and {SSN, Cust_name} are both super keys for the customer table.

    Candidate Key

    • Candidate keys are minimal super keys, meaning they have no proper subsets.
    • Candidate keys are essentially the primary key used in SQL.
    • Example: {SSN} is the candidate key for the super key {SSN, Cust_name} in the customer table.

    Primary Key

    • The primary key is chosen to uniquely identify tuples (rows) in a relation (table).

    Foreign Key

    • A foreign key in relation R is a set of attributes used to identify or refer to a tuple in another relation S.
    • R is the referencing relation and S is the referenced relation.
    • The foreign key in R must correspond to a superkey in S, which is typically the primary key of S.

    Cursor

    • A cursor is a pointer to a context area in PL/SQL.
    • It holds the rows returned by a SQL statement.
    • The set of rows held by a cursor is called the active set.

    Functional Dependency

    • Functional dependency describes a relationship between attributes in a relation (table).
    • If attribute A functionally determines attribute B, then the value of A uniquely determines the value of B.

    Database Management System (DBMS)

    • A collection of programs that enables user interaction with a database.
    • Provides functionalities for defining, constructing, and manipulating the database for various applications.

    Database System

    • The database and the DBMS software together constitute the database system.

    Advantages of DBMS

    • Controls data redundancy.
    • Restricts unauthorized access.
    • Provides multiple user interfaces.
    • Enforces integrity constraints.
    • Offers backup and recovery mechanisms.

    Disadvantages of File Processing System

    • Data redundancy and inconsistency.
    • Difficult data access.
    • Data isolation.
    • Data integrity issues.
    • Concurrent access is not possible.
    • Security problems.

    Data Abstraction Levels

    • Physical Level: Lowest level, describes how data is stored.
    • Logical Level: Describes the data stored and the relationships between them.
    • View Level: Highest level, describes only a part of the entire database.

    Integrity Rules

    • Entity Integrity: Primary key cannot have a NULL value.
    • Referential Integrity: Foreign Key can be NULL or a valid primary key value in another relation.

    Extension and Intension

    • Extension: The number of tuples in a table at any instance, which is time-dependent.
    • Intension: Constant values representing the table's name, structure, and constraints.

    Data Independence

    • Applications are independent of the storage structure and data access strategy.

    Relation

    • A relation is defined as a set of tuples.

    Degree of a Relation

    • The number of attributes in a relation schema.

    Relationship

    • An association among two or more entities.

    Relationship Set

    • A collection or set of similar relationships.

    Relationship Type

    • Defines a set of associations or a relationship set among a given set of entity types.

    Degree of Relationship Type

    • The number of entity types participating in the relationship type.

    Data Definition Language (DDL)

    • A language used to define the database schema through definitions.

    View Definition Language (VDL)

    • Defines user views and their mappings to the conceptual schema.

    Data Manipulation Language (DML)

    • Allows users to access and manipulate data organized according to the data model.

    DML Compiler

    • Translates DML statements into low-level instructions understood by the query evaluation engine.

    Query Evaluation Engine

    • Executes low-level instructions generated by the DML compiler.

    ###DDL Interpreter

    • Interprets DDL statements and records them in tables containing metadata.

    Query

    • User commands for interacting with a database.
    • Classified into DDL and DML.

    Correlated Subquery

    • A subquery referencing columns from the its parent query in its WHERE clause.
    • Columns from the subquery cannot be referenced elsewhere in the parent query.

    Product and Join Operations

    • Product: Combines every row from one relation with every row from another.
    • Join: Combines rows from one relation with related rows from another.
    • The resulting relations from these operations are not the same.

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    Description

    This quiz covers essential database concepts, focusing on triggers, stored procedures, super keys, and candidate keys. Test your understanding of how these elements function in database management systems and their significance in data integrity and performance.

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