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Introduction to Databases

• Databases are organized collections of related data.
• Data comprises facts that are recorded and have inherent meaning.
• Examples include names, phone numbers, and addresses.
• Databases represent aspects of the real world, often termed the "miniWorld".
• Any changes to the miniWorld must be reflected in the database.
• A database is a logically coherent collection of data, not just any random set of data.
• Databases are designed with a specific purpose, a target audience of users, and related applications.

Database Structure

• A database's structure is defined by the different types of files and records it contains.
• The structure must be carefully chosen to meet specific needs.
• Records within files are related to one another in certain ways.

Data Management Systems (DBMS)

• A DBMS is a general-purpose software system facilitating database definition, construction, manipulation, and sharing among multiple applications and users.
• Database definition involves specifying data types, data structures, and constraints for storage in the database.
• A DBMS stores the database definition as a catalog or dictionary, often called metadata.
• Building a database involves physically storing data on the system's storage media.
• Database manipulation includes functions such as querying to retrieve specific data, updating data to reflect changes in the miniWorld, and reporting on data.
• Database sharing allows concurrent access by multiple users and applications to a single database.

Relational DBMS Examples

• Oracle
• IBM DB2
• SAP Sybase
• Microsoft SQL Server
• Microsoft Access
• MySQL
• PostgreSQL

Database System Architecture

• A database system comprises a database and the DBMS software.
• Components include application programs, queries, software for processing queries, and accessing stored data and metadata.

Example: University Database

• A university database stores data on students, courses, and grades.
• It has five files: STUDENT, COURSE, SECTION, GRADE_REPORT, and PREREQUISITE.

Data Redundancy in File Processing Systems

• Data redundancy arises when multiple copies of the same data are stored in different files.
• This leads to wasted storage space, data inconsistencies, and difficulties in maintaining data updates.
• Changes to a file may need corresponding changes in multiple programs.
• Limited control over data access and maintenance.
• Longer development times for systems.

Advantages of Database Systems

• Data integrity, reduced redundancy, and data consistency are ensured.
• Data independence: programs are isolated from data storage details; changes to data structures do not require code changes.
• Data security via access control mechanisms.
• Data sharing: multiple users access and share data.
• Data integrity: DBMS enforces specific constraints that maintain data consistency.
• Data privacy: controls access to sensitive information.

Data Modeling

• Data modeling provides concepts for describing the structure of a database including entities, attributes, and relationships.
• Common modeling methodologies include Entity-Relationship (ER) diagrams.

Data Views

• Data views are specific perspectives or presentations of a database tailored to individual user needs.
• It may provide a subset of the database or incorporate derived data from other files.

DBMS Operations: Queries and Transactions

• Queries retrieve data from the database.
• Transactions encompass various data operations (reading, writing, updating, deleting).
• Proper transaction handling ensures data consistency.

Database Users and Roles

• End-users interact directly with the database.
• System administrators (or DBA) manage users and resources for the database system.
• Database designers define data structures and relationships.
• Application programmers create and maintain software for the database system.

DBMS Levels

• External level describes the portion of the database that's seen by a particular user.
• Conceptual level provides a high-level view of the entire database.
• Internal level provides the physical storage characteristics of the database.

DBMS Languages

• Data Definition Language (DDL) defines the database structure.
• Data Manipulation Language (DML) describes operations on the data.
• Data Query Language (DQL) is used for querying data.

Data Integrity and Security

• Database systems enforce data integrity and security constraints.
• Constraints specify permissible kinds of data to be stored in a database.
• They ensure data consistency and accuracy.