Basic knowledge about oracle Database 2

Basic knowledge about oracle Database 2

Oracle beginners series II

Basic Database knowledge

This article combs basic database knowledge that has been forgotten, and may not be remembered at all. In either case, remember it. If you cannot remember it, write it down.

First, I would like to ask the following questions:

What is the basic database knowledge?

Okay, let's get started with the directory.

My mailbox: appdevzw@163.com

Public Account: HopToad

Welcome from all walks of life

 

1. Basic Concepts

Concepts are concepts. Everyone should not be confused about these terms. But they must understand the definition, understanding can comprehend, and understanding can be used freely and then innovated.

1.1 data

Data is the symbol used to describe things and is the basic object stored in the database.Yes, that's right. It's a basic object. A database is used to store data. What does it save? Of course, data comes from the thing itself. Any thing contains a lot of information, and data needs to be abstracted from the thing. For example, my mailbox is appdevzw@163.com, my address, Hangzhou Binjiang, etc, next door Old Wang is also Hangzhou Binjiang. Well, this is not normal. His address data must be the same as mine.

1.2 Database

A DataBase is a set of data that is organized, described, and stored according to a certain data model. The data in the database has a small degree of redundancy and a high degree of data independence. data can be shared and managed by the database management system in a unified manner.

Note the following:

First of all, this is very important based on a certain data model, instead of making some data together;

The second point is relatively small redundancy and high data independence. This is relatively small and high, which is comparable to some of the legal provisions of our country. There is no specific indicator to consider ~

Third, we can achieve data sharing and unified management. This is very important. It is difficult to achieve this without the above features.

1.3 Database Management System

DataBase Management System (DBMS) is the System software used to manage databases.

For example, ORACLE, SYBASE, And my SQL.

1.4 Database System

A database system is formed after the database and database management system are combined with the computer system. Generally, database systems are composed of databases, operating systems, database management systems, development tools, application systems, database administrators, and database user groups.

For example, after an ORACLE is installed, a database is created, and then the operating system and application system on the server are used as the database system.

2. database features

There are four basic concepts. Remember to get started. Haha

Then let's take a look at the features of the database. These features are exactly the same as described in the Database concept.

2.1 Data structuring

In the conceptData ModelAll applications are organized, not a specific application. Isn't the storage structure of the program itself oriented to an application?

2.2 sharing

Databases are designed for the entire system and serve multiple users and applications. All data needs to be shared to reduce data redundancy for different applications and provide data consistency.

2.3 independence

Independence is mainly to consider the relationship with the application, decoupling the database from the application, so that the database can run independently of the application.

2.4 unified management and control

Considering the difficulty of achieving the above three points, it is difficult to think about it. We have to have a system, that is, the database management system, to manage data security, integrity, concurrency, backup, and recovery in a unified manner.

3. Data Model

In the Database concept, the database is organized according to a certain data model, so there are two problems.

A) What is a data model?

B) Why is this data model required?

These two questions are answered together.

Let's expand it,

Data Model:InSoftware EngineeringData Model is definedDataHow to input and outputModel. It includes three main elements: data structure, data operations, and data constraints.

Looking at the three major elements of the data model, I was amazed. I remember that the data structure was an important course in the computer science field, and the mechanical nature of the data structure was born, and it was quietly drifting here.

In fact, the three major elements are the supplement of the digital-analog model concept, and the expansion of the data model concept is the three major elements concept. Of course, this understanding may not be appropriate. Remember one sentence first:Data Model is the abstraction of data features.

Data Models are divided into three types based on different application layers: Conceptual Data Model, Logical Data Model, and physical data model.

Data Models are divided into hierarchical models, mesh models, relational models, and object-oriented models based on different data structures.

The first question is basically finished here. Let's proceed.

Second, let's look at the data model, which can be understood based on the classification of application layers. The conceptual data model is a world model oriented to database users and used to describe the conceptual structure of the world, this model is independent of all database management systems. The logic model is visible to users and also related to the support of the database management system. This model is user-oriented and system-oriented; A physical model is a computer-oriented model that describes the organizational structure of data on the media. It is related not only to the database management system, but also to the operating system and hardware.

At this point, we understand that the data model describes how data is stored on our computers step by step. Isn't that the concept of a database.

 

4 Database System Design Steps

The database design is divided into six phases:

1) Demand analysis stage

Collect System Requirements and create Requirement Description documents.

This is to know what the customer needs.

2) Conceptual Structure Design Stage

The requirements are summarized and abstracted to form a conceptual model independent of a specific DBMS.

This is not a conceptual data model.

3) Logical Structure Design Stage

A logical database model supported by DBMS is derived based on the conceptual model. This model must meet the user needs of database access, consistency, and operation.

This is the logic data model design.

4) Physical Structure Design Stage

Select the physical structure that best suits the application environment for the Logical Data Model.

Well, this is the physical data model design.

5) database implementation stage

Establish a database based on the above design structure, and test run the database system at the same time.

Coders started coding.

6) Database Operation and Maintenance

The above five stages are the database development and design stages, and the test section has been summarized.

At last, it was the turn of DBA to show up.