A data is a symbolic representation of a quantitative or qualitative attribute or variable.

Symbolic: it can be numeric, algorithmic, alphabetical, spatial, and so on.

Quantitative: data that is always referred to numbers.

Qualitative: they are those that answer the question, which. Here may exist data such as color, feelings, etc.

Data are information, so they describe empirical facts, events, and entities.

In order to analyze the data, first we have to organize them or tabulate them. The processing of the data is what will provide us with the respective information, when we talk about a data set.

Database Concepts

Database: is a set of information that belongs to the same context. Data set that is systematically structured and stored.

Table: type of data modeling where the data that is collected by a program is stored. We could say that a table is similar to a spreadsheet, in that the data is stored in rows and columns.

The tables are composed of two structures:

1. The field that refers to the name of the column, which must be unique and have an associated data type.
2. The records that correspond to each row in the table, where the data and records are composed.

Why is it important to use a database?

1. Greater independence.
2. Greater availability.
3. Greater security.
4. Reduced redundancy: a single piece of data can be used by multiple files, avoiding replication.
5. Greater efficiency in data capture, encoding, and entry.
6. Greater coherence.
7. Greater efficiency.
8. Greater informational value.

Data Model: shows the logical structure of the database, including the relationships and constraints that determine how the data is stored and accessed. It is a collection of conceptual tools to describe the data, their relationships, semantics, and consistency constraints. Data models provide a way to describe the design of the database at the physical, logical, and view levels.

Data models can be classified as:

1. Entity-Relationship (E-R) Model, which is based on a perception of the real world consisting of a collection of basic objects called entities and the relationships that exist between them.

* An entity is a thing, a real-world object that is distinguishable from other objects.
2. Relational Model, which is a collection of tables to represent both the data and their relationships, and it is the most widely used model.
3. Object-Oriented Data Model, which can be considered an extension of the entity-relationship model, incorporating concepts such as encapsulation, methods or functions, and object identity.
4. Semi-Structured Data Model, which allows the specification of data where individual data elements of the same type may have different sets of attributes.
5. Network Data Model.
6. Hierarchical Data Model.

Uses of Entity-Relationship Diagrams:

1. Database design.
2. Database problem-solving.
3. Enterprise information systems.
4. Business process reengineering (BPR).
5. Education.
6. Research.

Basic Notions of Entity-Relationship Model:

1. Set of Entities.
2. Set of Relationships.
3. Set of Attributes.

Set of Entities: entities that share the same properties or attributes. Entities are typically represented by rectangles. An entity has a set of properties.

Set of Relationships: a relationship is an association between two or more entities, represented by a diamond.

Set of Attributes: attributes are represented by ellipses, which describe properties possessed by each member of a set of entities. Within each entity, there must be an attribute that serves as an identifier.

Database Management System (DBMS), or Sistema Gestor de Base de Datos in Spanish, is a collection of programs whose objective is to serve as an interface between the database, the user, and the applications. Another way to explain it is that the DBMS acts as a client in managing the database and communicates with the server.
Characteristics of a DBMS:

1. Information abstraction.
2. Independence.
3. Minimal redundancy.
4. Consistency: ensuring that redundant information is updated consistently.
5. Security.
6. Integrity.
7. Backup and recovery.
8. Concurrency control: simultaneous access to the database management system.
9. SQL makes use of relational algebra and calculus to retrieve information from our database.

DISTINCT: is used to avoid retrieving duplicate records based on a certain field. For example:
SELECT DISTINCT names FROM professors;

Note: Not all database systems support the SELECT TOP clause. MySQL supports the LIMIT clause to select a limited number of records, while Oracle uses FETCH FIRST n ROWS ONLY and ROWNUM.

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