9618 · 8.2
Database Management Systems (DBMS) flashcards
Revision flashcards for Cambridge 9618 Database Management Systems (DBMS) (syllabus 8.2). Flip, recall, then mark a real past-paper question.
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What is a DBMS (Database Management System)?
A software package that enables users to define, create, maintain, and control access to a database. It acts as an intermediary between the user and the database.
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What is Data Definition Language (DDL)?
The component of a DBMS used to define the database structure and schema. Commands include CREATE TABLE, ALTER TABLE, and DROP TABLE.
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What is Data Manipulation Language (DML)?
The component of a DBMS used for managing data within the schema. Commands include SELECT, INSERT, UPDATE, and DELETE.
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What is Data Control Language (DCL)?
The component of a DBMS used to control access and permissions for users. Commands include GRANT and REVOKE.
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What is the Data Dictionary?
A centralised repository of metadata (data about data). It stores definitions of all schema objects, such as table names, column names, data types, and constraints.
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What is Data Independence?
The ability to modify the database schema at one level without affecting the schema at a higher level. There are two types: physical and logical.
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What is Physical Data Independence?
The ability to change the physical storage of data (e.g., moving to a new hard drive, changing file organisation) without affecting the logical schema or application programs.
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What is Logical Data Independence?
The ability to change the logical schema (e.g., adding a new column to a table) without having to rewrite existing application programs. This is harder to achieve than physical independence.
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What is Concurrency Control?
The DBMS's mechanism for managing simultaneous operations on the database by multiple users without them interfering with each other. This prevents data inconsistency.
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What is a key benefit of a DBMS regarding data integrity?
A DBMS enforces data integrity rules (e.g., data types, constraints, referential integrity) centrally, ensuring that all data entering the database is valid, regardless of the application used to enter it.
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Common mistake: Confusing DDL and DML.
DDL defines the 'container' (the table structure). DML manages the 'contents' (the data inside the tables). Remember: Definition vs. Manipulation.
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What is the role of a DBMS in backup and recovery?
A DBMS provides mechanisms to automatically back up the database and restore it to a consistent state after a hardware or software failure, ensuring data durability.