Introduction to Database Systems Study notes-Chapter One introduction

Introduction to the database System--Chapter I. INTRODUCTION

• Written in front: Winter holiday, except relatives and classmates dinner, King Glory and other games on the game to spend a little time, self-thought to take a little time to learn the database and Android, to the next semester and build a project to lay a lost foundation. In order to spur themselves, set a small goal ( one billion ), each three days I will publish a database or Android learning notes. Or the words that your talent can't hold your ambition, then calm down and learn .

Database System Overview

Terminology and basic concepts commonly used in databases

Basic concepts of databases

• ( data )

data is the basic object stored in the database , you can define the data as follows: The symbolic records describing things are called data; symbols describing things can be numbers, text, images, graphics, sounds , etc. is a format or method of representing and storing data in a computer.

name	Sex	Date of birth	Place of birth	our Department	Admission Time
Li ming	Man	19980202	Sichuan Province	Computer Department	2016

The computer is often described as: (Li Ming, Male, 19980202, Sichuan, computer Science, 2016) the student's name, gender, etc. are organized together to form a record . The student record here is a description of the student's data. Such data are structured.

• databases (database , DB)

A database is a warehouse where data is stored and stored in a certain format. Strictly speaking, the database is a long-term existence in the computer, organized, shareable a large number of data sets. * Data are organized, described and stored according to a certain data model, with smaller redundancy and higher data independence.
The database has: permanent storage, organized, can share three basic features.

• Database Management Systems (DB Management system DBMS)

The database management system is a layer of data management software which is located between the user and the operating system.

• Basic functions of database management system
  • Data definition Features
  • Data organization, storage and management
  • Data manipulation functions
  • Management and operation of database affairs
  • Establishment and maintenance of database
  • Other features

• Database Systems (DB system DBS)

database system refers to the system which is introduced into the database, which is composed of database, database management system, application system and database administrator.

The development process of data management

Data Management refers to the classification, organization, coding, storage, retrieval and maintenance of the data, which is the central problem of processing. Data processing refers to the collection of various data, storage, processing and dissemination of the sum of a series of activities.

• Human Management Phase (the 1950s)

• 1. Data not saved
• 2. Application Management Data
• 3. Data is not shared: Data is program-oriented, and a set of data can only correspond to one program

• 4. Data is not independent

• File System Phase (20th century 50-60 generation)

• Features of file System Management data
  • 1. Data can be stored for a long time
  • 2. File System Management Data
• The file system has the following disadvantages
  • 1. Poor data sharing, large redundancy
  • 2. Poor data independence

• Database System phase (after the 1960s)
• See below

Characteristics of the database system

• Structured data
  The database system realizes the structure of the whole data, which is one of the main characteristics of the database. The so-called "overall" structure refers to the data in the database is no longer only for an application, but for the whole organization, the data is connected.

• High data sharing, low redundancy, easy expansion
  The database system looks at and describes the data from a holistic perspective, and the data is no longer oriented to an application but to the entire system, so data can be shared by multiple users and multiple applications. Data sharing can greatly reduce data redundancy and save storage space.

• High data independence
  • Physical independence: The data is independent of the user application and the database stored on disk.
  • Logical independence: The user's application and the logical structure of the database are independent of each other

Data independence is guaranteed by the DBMS's level two image feature.

• Unified management and control of data by DBMS

DBMS must provide several aspects of data control functions

• Secure (security) protection of data
• Data integrity (Integrity) Check
• Concurrency (Concurrency) control
• Database Recovery (Recovery)

A database is a large, shared collection of data that is stored in a computer for long periods of time

Data model

The data model is an abstraction of the real-world data characteristics, which means that the data model is used to describe the data, organize the data, and manipulate the data.

Component elements of the data model

• Data

  There are two types of data structure Description: One is related to the type, content, nature of the object, and a class of objects related to the connection between data. The data structure is a collection of the described object types, and is a static description of the system.

• Data manipulation

  Data manipulation refers to a collection of instances (values) of various objects (types) in the database that allow operations to be performed, and the database is primarily queried and updated (including insert, modify, delete) two large classes of operations. is a description of the dynamic operation of the system.

• Integrity constraints for data

  The integrity constraint of the data is a set of integrity rules. Integrity rules are the constraints and dependencies of data and their relationships in a given data model to limit the state of the database and the state of the data model. The data model should reflect and prescribe the basic general integrity constraints that this data model must adhere to.

Three main data models

• * * Hierarchical Model * *

  The hierarchical model uses a tree structure to represent various entities as well as the relationships seen by entities.

This is a summary link to the "tree" chapter of Java Learning

• A basic feature of the hierarchical model is that any given record value can show its full meaning only if it is viewed by its path, and no child record value can exist independently from the parent record value.
  

• Hierarchical model data manipulation and integrity constraints: no corresponding parent node value can not insert its child node value, if the parent node value is deleted, then the corresponding child node value is also deleted.

• Mesh model

  In the database, putting the satisfies (1) allows more than one node without a parent (2) a node can have more than one parent condition of the basic hierarchical contact set called the mesh model.

• Personal sensory mesh model to some and a graph similar
  This is a summary link to the "diagram" chapter of Java Learning

• Relational model

• Data structure of relational model
  • Relationship: A relationship refers to a table
  • Tuples: A row in a table is a set of
  • Properties: A column in a table is a property
  • Code: A property group in a table that uniquely identifies a tuple
  • Domain: The value range of a property
  • Component: A property value for tuples
  • Relationship patterns: A description of the relationship

The relationship model requires that the relationship must be normalized, that is, the requirement relationship must meet certain normative conditions, and the most basic one is that each component of the relationship must be an irreducible data item, and no table is allowed in the table.

Database system Architecture

From the point of view of database management system, the database system usually adopts three-level pattern structure, which is the system structure inside the database management system.
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 and so on. This is the architecture outside the database system.

• Concepts of "type" and "value"
  • "Type" means a description of the structure and properties of a class of data
  • "Value" is a specific assignment of the type

• Pattern: The logical structure and characteristics of all data in a database are described, only the description of the type is involved, and no specific value is involved.

  Three-level schema structure of database system

• Mode

  Schema, also known as logical mode, is a description of the logical structure and characteristics of all data in the database, and is the public view of all users. There is only one schema for a database. It is the middle tier of the database system schema structure. DBSM provides schema description language (schema DDL) to strictly define patterns.

• External mode

  The external mode is a description 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. Outer mode is a subset of patterns. A database can have multiple external schemas. DBSM provides a sub-schema description Language (sub-schema DDL) to strictly define sub-schemas.

• Internal mode

  A database has only one internal mode. It is a description of the physical structure and storage of the data, and is how the data is represented inside the database. DBSM provides internal mode description Language (internal mode DDL) to strictly define inner mode

Two-level image system architecture for the database

• * * External mode/mode image

  The schema describes the global logical structure of the data, and the external schema describes the local logical structure of the data. Each external mode, the database system has an external mode/mode image, which defines the corresponding relationship between the external mode and the pattern. When the schema changes, there is a database administrator to change the image of each external mode/mode, which can keep the external mode unchanged.

• Mode/Internal mode image

  There is only one pattern in the database, and there is only one inner mode, so the schema/internal schema mapping is unique, it defines the correspondence between the global logical structure of the data and the storage structure.

Summary

Took a little time to write this summary, there are some knowledge points or summary is not in place, the knowledge of the collation of some is not reasonable, the latter will slowly increase the change. Spent a day or so to read the introduction of the database system introduction, in the process of writing this summary there is always a thought is in the end should not write, write whether there is no use. In fact, there is no use I do not know, but since the decision to write, it is necessary to continue to write down, decided to go deeper understanding do not stop. Put your ideas to work to achieve this is the thing to do!

Introduction to Database Systems Study notes-Chapter One introduction