Database Essentials: Concepts, Architecture, and Management

Core Database Concepts

Registration

The set of fields that describe an object.

Field

A feature of an object that stores a value.

Database

A collection of records or data that contain relevant information.

Database Applications

Databases are fundamental across various sectors, including:

• Banks
• Airlines
• Universities
• Credit Card Transactions
• Telecommunications
• Finance
• Sales
• Production
• Human Resources

Levels of Data Abstraction

Physical Level

This is the lowest level of abstraction, describing how data is actually stored.

Conceptual Level

This is the next higher level of abstraction, describing what data is stored in the database and the relationships between data.

External Level (View Level)

This is the highest abstraction level, describing only a part of the database relevant to specific users.

Data Models

Register-Based Logical Models

Used to describe data at the conceptual and external levels.

Physical Data Models

Used to describe data at the lowest level. Unlike logical data models, very few physical models are commonly used.

Database Administrator (DBA) Role

The Database Administrator (DBA) is the person in charge and has full control over the database system. Its main functions include:

• Schema Definition

  The original database schema is created by writing a set of definitions, which are translated by the DDL compiler into a set of tables permanently stored in the data dictionary.

• Definition of Storage Structure and Access Methods

  This involves creating appropriate storage structures and access methods by writing a set of definitions, which are then translated by the data storage and definition language compiler.

• Granting Data Access Authorization

  This allows the database administrator to regulate which parts of the database can be accessed by different users.

• Specifying Integrity Constraints

  These are a series of restrictions stored in a special system structure, accessed by the database manager whenever a system update is performed.

Database User Types

Sophisticated Users

These users interact with the system without writing programs, instead formulating their queries in a database query language.

Specialized Users

Some users write sophisticated, specialized database applications that do not fit within the traditional data processing framework.

Naive Users

These unsophisticated users interact with the system by calling one of the permanent application programs previously written for the database system. A naive user is essentially an end-user who utilizes the database system without needing to understand its internal design; for example, a cashier.

ANSI 3-Schema Database Architecture

The ANSI/SPARC architecture defines three levels of database abstraction:

Internal Level

This level has an internal schema that describes the physical storage structure of the database. It uses a physical data model, and the only data that truly exists is at this level.

Conceptual Level

This level has a conceptual schema that describes the structure of the entire database for a community of users. It hides physical storage details and works with logical elements such as entities, attributes, and relationships.

External Level (View Level)

This level has several external schemas or user views. Each schema describes a specific view of the database for a group of users, hiding the rest.