Introduction to the--1 of database system

1. Four basic conceptual data of the introduction 1.1 database

Symbolic records describing things are called data.

The meaning of data is called the semantics of data, and the data is inseparable from its semantics. If the semantics of data 93 can be scores, numbers

Database

Refers to a long-term, organized, shareable collection of large amounts of data.

With a small redundancy, high data independence and ease of scalability

Database management System

is the basic software of a computer.

Function:

Data definition Features

Data organization, storage, and management

Data manipulation Capabilities

Transaction management and operation management of the database

Database building and Maintenance functions

Other functions (such as communication between database systems and other software systems in the network)

Database system

A system consisting of databases, database management systems, applications, and database administrators to store, manage, process, and maintain data

1.2 Data Model

The data model is an abstraction of the characteristics of real-world data.

according to the different purpose of the model application, it is divided into conceptual model, logical model and physical model.

Conceptual model

Also known as the information model.

Model data and information according to the user's point of view.

for database design.

Extended:

Logical model

including hierarchical model, mesh model, relational model, object-oriented data model, object relational data model, semi-structured data model, etc.

Model data according to the computer system's point of view.

For the implementation of the database management system.

Physical model

Describes how the data is represented and accessed within the system, and is intended for computer systems.

The abstraction of the lowest level of data

The implementation of the logical model to the physical model is mainly implemented by the database management system.

Data Model components: data structure, data manipulation, integrity constraints

Data

Describes the constituent objects of a database and the connections between objects

is a collection of the described object types and is a description of the system's static characteristics.

Data manipulation

A collection of actions that are allowed to be performed on instances (values) of various objects (types) in a database, including operations and related operational rules

is a description of the dynamic characteristics of the system

Integrity constraints for data

is a set of integrity rules

Basic and general integrity constraints that reflect and stipulate the data must be observed (divided into entity integrity, referential integrity constraints)

use of the data Model :

Transform all the involved objects of the real world into conceptual models

Design a conceptual model into a logical model

The database management system is responsible for translating the logical model into a physical model

1.2.1 Conceptual model

Key Concepts

Entity entities: objects that exist and can be distinguished from each other, abstract concepts or relationships, can all be called entities. such as: A student, an elective course, a working relationship between the teacher and the faculty

Property attribute: An attribute that an entity has is called a property. such as the time of admission, name

Code key: A property that uniquely identifies an entity. such as school number

Entity entities Type: A class of entities and the common attributes they have. such as students (school number, name ...) ）

An entity set entity set: A collection of entities of the same type. Like all students

Contact Relatioship: A connection between entities (usually referred to as a link between entity sets). A pair of one or one-to-many, many-to-many

Representation method

Entity-contact method, described by E-r diagram

1.2.2 Logical Model

The main logical data model:

Hierarchical Models && Mesh models

The hierarchical model and the mesh model are collectively referred to as the format model

The unit of data structures in a formatted model is a basic level of contact (two records and one-to-many links between them)

Hierarchical model

There is only one root node (the root node has no parent nodes).

Each non-root node has only one parent node.

Mesh model

You can have multiple root nodes.

Each non-root node can have multiple parent nodes.

Advantages: High Query efficiency

Disadvantages: Complex structure, poor data independence, poor scalability, difficult to use, difficult to maintain.

Relational model

Based on rigorous data concepts.

Correspondence Relationship:

Relationship--table

Tuples--Rows

Code--An attribute group

Domain--a set of values that have the same data type. The value range of a property is derived from a domain

Component-a property value in a tuple

Relationship pattern--a description of the relationship. such as the relationship name (attribute 1, property 2, ..., attribute N)

Principle:

Each component of a relationship must be a non-divided data item

three major integrity constraints:

Entity integrity, referential integrity, user-defined integrity

Advantages: High data independence, strong scalability, easy to understand and easy to maintain.

Disadvantage: The query efficiency is lower than the formatted data model. The DBMS must optimize the user's query request

Object-oriented data model

Object Relational Data Model

Semi-structured data model

1.3 Structure of the database system

From the perspective of the database application developer, the database system typically uses a three-level schema structure (internal structure).

From the point of view of database end user, the structure of database system is divided into single user structure, master-slave structure, distributed structure, client-server, browser-Application server/database multi-layer structure, etc. (external structure).

Schema schema

A description of the logical structure and characteristics of all data in a database

Description of only type type involved

Example instance

A specific value of the pattern

Three-level mode structure

External mode

Also known as sub-mode or user mode

A description of the logical structure and characteristics of the local data that the database user, including the application and end users, can see and use

Is the data view of the database user

is a logical representation of the data associated with an application.

Mode

Also called logical view

is a description of the logical structure and characteristics of all data in the database

is a public data view for all users

Internal mode

Also known as storage mode

Is the description of the data physical structure and storage method

is to organize the data structures that are defined in the global logical structure and their linkages according to a certain physical storage strategy

Is how the data is organized inside the database

Level two image feature

External mode/mode image

When the mode changes, the external mode/mode image is changed so that the external mode does not change

Applications are written in an out-of-the-way mode, and applications do not change, ensuring logical independence between data and programs

Mode/Internal mode image

Changes in the mode/internal mode image when the storage structure of the database changes, so that the mode does not change

Ensures the physical independence of data and programs

1.4 Composition of the database system

Hardware platforms and databases

Memory, disk, data transfer

Software

DBMS, DBMS-enabled operating system, advanced language development/compilation tools with DB interface, DBMS-centric application development tools

Personnel

DBA, System analyst, application programmer, user

1.4.1 DBA Responsibility

Determine the content and structure of information in a database

Determine the storage structure and access policy of the database

Defining security requirements and integrity constraints for data

Use and operation of monitoring database

The improvement and reorganization of database and reconstruction

Introduction to the--1 of database system