Understanding Database Concepts: Definitions and Models
Understanding Database Concepts
Tip: A set of characters that have a specific meaning.
Information: Specific data according to user needs.
Field: A space filled with requested data.
Registration: Fields of similar or different types filled with information.
File: A collection of records following a defined structure.
Database: A collection of files created to encompass and reduce information. Its three components are hardware, DBMS software, and the data being handled.
DBMS (Database Management System): Its objective is to store, use, and manipulate information within the database.
Database Schema: A logical organization of data.
DBA (Database Administrator): A professional responsible for managing the database.
Data Abstraction
There are three levels of data abstraction:
- Physical Level: The lowest level.
- Conceptual Level: The highest level of abstraction.
- View Level: The final view or result.
Data Definition and Relationships
Data Definition: Describes the data type and length of a field, including attributes (features), data, and total record concept.
Relationship between Data: Defined as the relationships between data types of records, linking them together.
Data Models
Data Model: A simulation of reality.
Primary Key: Key attributes that uniquely identify a single entity.
What is Data Modeling?: The collection of conceptual tools for describing data, relationships between them, associated data semantics, and consistency restrictions.
Types of Data Models
There are three main types of data models:
- Object-based logical model
- Record-based logical model
- Physical data model
The object-based logical model describes data at the conceptual and view levels.
The Entity-Relationship (ER) model represents reality through entities.
Tangible entities are those we can touch, while intangible entities are those we cannot see or touch.
The characteristics of database entities are called attributes.
The record-based logical model is used to register and represent reality, as well as the relationships between entities.
The three sub-models are:
- Relational Model
- Network Model
- Hierarchical Model
The relational model displays relationships between tables through rows (tuples) and columns (attributes).
The network model represents data through collections of records, with relationships represented by links.
The hierarchical model is similar to the network model, but data is organized in a tree structure instead of a graph.
The physical data model describes data at the lowest level and includes unified models of ASIC and memory.
Instances and Schemas
Instance: The state of a database at a given time, including data and accumulated updates.
Schema: The logical description of the database, providing names of entities and their attributes.
Data Independence
Physical Data Independence: The ability to modify the physical schema without requiring changes to the conceptual schema.
Logical Data Independence: The ability to modify the conceptual schema without requiring changes to application programs.
Data Definition Language (DDL)
DDL is used to define the database schema through a series of definitions expressed in a specific language. The result is a data dictionary.
Data Manipulation Language (DML)
There are two types of DML:
- Procedural DML: Requires the user to specify both the data needed and how to retrieve it.
- Non-Procedural DML: Requires the user to specify only the data needed, without specifying the retrieval method.