Introduction to Database Chapter 1

Introduction to Database Systems (fourth edition)

Introduction to the first chapter

Data: The symbolic records describing things are called data, which can be digital, text, graphics, images, sounds, languages, etc., and various forms of data can be digitized and stored in a computer.

Database: A collection of large amounts of data stored in a computer, organized, and shareable over a long period of time.

The data in the database is organized, described and stored according to a certain data model, which has small redundancy, high data independence and expansibility, and can be shared for various users.

A database management system (DBMS) is a layer of data management software that is located between the user and the operating system. The main functions are:

data definition function;

Data organization, storage and management;

Data manipulation function (increase and deletion check);

Transaction management and operation management of database;

The establishment and maintenance function of database;

other functions;

The three phases of data management include: the human management phase, the file system phase, and the database system phase.

Features of the database system:

Data structure (is one of the main characteristics of the database, but also the essential difference between the database system and the file system)

High data sharing, low redundancy, easy expansion

High data independence (including physical independence and logical independence)

Unified management and control of data by DBMS

Data model is the core and foundation of database system. Can be divided into two categories, one is the conceptual model, one is the logical model and the physical model. The first type of model is mainly used for database design, and the second is for DBMS implementation.

Component elements of the data model:

Data structures (hierarchy, mesh, and relational structures are named as hierarchical models, mesh models, and relational models, respectively)

Data manipulation (query and update two major categories)

Integrity constraints for data

Links between two and more than two entity types: one-to-many, one-to-many, many-to-more

The E-r diagram provides methods for representing entity types, attributes, and contacts:

Entity type: The rectangle is used to indicate the name of the entity in the rectangle box;

property, represented by an ellipse, and connected with a non-oriented edge to the corresponding entity type.

Contact: With a diamond, the diamond box is indicated by the contact name, and the non-oriented side with the relevant entity type connected together.

The hierarchical database not only stores the data itself, but also stores the hierarchical relationships between the data. There are two common ways to implement this:

Adjacency method and link method.

The commonly used methods of network structure are: Link method (including one-way link, bidirectional link, ring link, link to the first, etc.), as well as the Guide element array method, binary array method, index method and so on.

Relational model

The three-level pattern structure of the database system is that the database system is composed of the outer mode, the mode and the internal mode three.

A database has only one mode and one internal mode, and multiple external modes.

A pattern, also known as a logical pattern, is a description of the logical structure and characteristics of all data in a database, and is a common view of all users ' data.

The external mode is the contempt of the logical structure and characteristics of the local data that the database user can see and use, and is the data view of the database user.

The internal mode is also the storage mode, which is the description of the data physical structure and storage method, and is the representation of the data inside the database.

The database management system provides a two-layer image between level three modes:

External mode/mode image

Mode/Internal mode image

These two layers of images ensure that the data in the database system can be more specific logical independence and physical independence.

Introduction to Database Chapter 1