Introduction to Databases

Introduction to Databases

• Data: Known facts that can be recorded and have an implicit meaning (e.g., names, mobile numbers, grades).
• Information: Data that is processed and organized to be meaningful.

File Based Systems

• File-based systems: Early attempts to computerize manual filing systems. They work well for small amounts of data, but not for large numbers of items or complex analysis.
• Disadvantages of file-based systems:
  • Data Isolation: Difficult to access information scattered across different files due to varying formats.
  • Data Redundancy: Duplicated data in separate systems can lead to inefficiencies, inconsistency and wasted resources.
  • Data Dependence: Changes in data structure require complex code modifications.
  • Integrity Problems: Difficult to enforce constraints (e.g., salary limits) and atomicity (transactions completing entirely or not at all).
  • Security Problems: Limited control over access rights and auditing capabilities.
  • Limited Data Sharing: Only one user can access a file at a time.
  • Disaster Recovery: Limited or non-existent recovery from hardware or software failure.

Database Systems

• Database: A collection of related data.
• Database Management System (DBMS): Software that enables users to create, maintain and interact with databases, defining, constructing, and sharing them.
• Database Application: Programs interacting with the database during execution.
• Miniworld: The real-world aspect represented by the database.

DBMS Functions

• Defining a database: Specifying data types, structures, and constraints. This definition is stored as metadata in a database catalog.
• Constructing a database: Storing data on storage media controlled by the DBMS.
• Manipulating a database: Querying, updating, deleting, and retrieving data.
• Sharing a database: Allowing multiple users and programs simultaneous access.
• Protecting a database: Providing system protection against hardware/software failures, and security protection against unauthorized access.

Database Advantages

• Control of data redundancy: Integrating files to avoid redundant copies of the same data.
• Data consistency: Updates are performed once and available immediately to all users.
• Data sharing: Simultaneous access for multiple users.
• Improved data integrity: Enforcing data constraints to ensure accuracy.
• Multiple views of the data: Providing different perspectives of the data for various users.
• Improved security: Enforcing security measures against unauthorized access.
• Program data independence: Reducing dependence on data structures.
• More information from the same amount of data: Data can be analyzed and used in different ways.
• Improved backup and recovery services: Robust mechanisms to restore data.

Database Languages

• Procedural Languages: Users specify data requirements and how to retrieve them.
• Declarative (nonprocedural) Languages: Users specify data requirements without detailing retrieval methods.
• Data Definition Language (DDL): Defines database structure (tables, attributes, data types, and constraints).
• Data Manipulation Language (DML): Manipulates data within the database (insert, update, delete, retrieve).
• Query: A statement requesting data retrieval.

Database Environment

• Users: Databases are used by various individuals and systems, including students, teachers, administrators, and application systems.
• DBMS Examples: Oracle, MySQL, Access.
• Database Roles:
  • Database Administrator (DBA): Responsible for authorizing access, coordinating use, monitoring performance, and acquiring resources.
  • Database Designer: Identifies data to be stored and chooses appropriate database structures.
  • End Users: Access the database for querying, updating, and reporting.
  • System Analysts and Application Programmers: Translate end-user requirements, interact with database designers, and develop database applications.

When Not to Use Databases

• Consider regular files for simple, well-defined applications that are not expected to change, embedded systems with limited storage, and applications with no multi-user access.

An Example: University Database

• Information: Stores data about university students, courses, and grades.
• Data Records: Students, Courses, Sections, Grade reports, Prerequisites.
• Database Catalog: Stores metadata about the database (e.g., table names, data types, constraints).

Benefits of Databases

• Data Management: Provides a structured, efficient way for storing and managing data that is more flexible and secure than traditional file-based systems.
• Enhanced Information Retrieval: Makes it easier to access and analyze data to get insights and make better decisions.
• Improved Data Integrity: Ensures consistency, accuracy, and reliability of data with data constraints.
• Shared Access and Collaboration: Enables multiple users to access and manage data simultaneously.
• Scalability: Can accommodate growing amounts of data and user demands.