[Test] database system principle-detailed explanation (Chapter 1), detailed explanation of legend monster Database

[Test] database system principle-detailed explanation (Chapter 1), detailed explanation of legend monster Database

I still remember the first time I read this book, it was very messy, especially the three or four chapters. I didn't understand this book very well. I just drew two flowcharts and did not dare to post them, I hope you can get your guidance.

The topic of the following blog is the first chapter:

After the explanation by Mr. Mi that morning, he no longer feared this book. As Mr. Mi said, he thought it was very simple, but the fact was that it was very simple. Let's take a look at how simple it is!

This chapter focuses on some basic concepts. Although the basic concepts are boring, they cover the content of the entire book. This chapter mainly covers two categories:Data and database. Data includes the development of data management technology and the description of data to abstraction. Databases include database systems and database management systems.

 

1. Historical Development of Data Management Technology

With the development of the times, the amount of data has become more and more, so we cannot use the traditional manual method to process data. At this time, the data management technology has emerged. It has gone through four stages: manual management, file system, database, and advanced database. That is, fromProfile Program-application-oriented application system-object-oriented development.

 2. Data description to abstraction

The process from data description to abstraction is from the specific representation in the computer to the database design.

Data description has gone through three stages: Concept, logic, and physical

1. concept description:Speaking of concepts, We have to contact entities, entity sets, attributes, and entity identifiers.We can regard an object as an object. An object has attributes and has a unique name, that is, an identifier. The object set is the class, that is, the object set.

2. logical description:An object contains multiple attributes. It is equivalent to a record in the database, and each attribute in the record is a field. Multiple records constitute a file, the key code uniquely identifies these records.

3. Physical description:Physical descriptions are used to describe the units used to store data. For example, bit, byte, word, block, etc.

However, entities are not isolated from each other, and they are associated.

The above three articles are about the representation of data in the computer, so how can we turn it into reality. Changing from a computer to a real world is an abstract process.

The four models of database design are shown in the figure below:

(1) the conceptual model serves users and database designers to communicate with each other. It is based on user requirements and the overall logical structure of data.

(2) The logical model serves database designers and programmers to communicate with each other. Based on database implementation, it expresses the overall logical structure of the database.

(3) The Internal Model stores data, and the External Model is the part of data used by the user.

Layer-3 mode and two-level image:

The layer-3 mode is the right half of the graph. It represents the entire process from database storage to database logic implementation to user data. There are two images. First, the images from the external mode to the logical mode are stored in the external mode, and then the images from the internal mode to the logical mode are stored in the internal mode.

3. DBMS and DBS

We can distinguish from one definition: DBS are a collection of DBS, hardware, software, and DBAs. DBMS is a core component of DBS, that is, DBS include DBMS.

DBMS working mode:

DBMS accepts data requests from applications, converts them to lower-layer commands, operates databases, processes database query results, and then reports the results to users.

DBMS main functions:Here we will feel familiar with it. Isn't DDL or DML the thing we just learned? The database protection function is just a new name, it is not the DCL we have learned before. I also learned DD before.

Let's look at DBS again. We mentioned above that it is composed of DB hardware, software, and DBA. The global structure of DBS is to connect modules from four levels: disk-DBMS-interface-user.

Summary: This course by Mr. Mi makes us feel that learning is very simple. We should be good at finding relationships, turning new knowledge into old knowledge, and making knowledge no longer isolated.

Principles of Self-tested Database Systems

The main task is to design a database with reasonable structure, convenient use and high efficiency for a department and organization according to application requirements with the support of DBMS.
Gain an in-depth understanding of the working principles of the database system and master the use of Data Language SQL.

2011 answers to the principles of the Self-tested Database System

I want to find the answer to the principle of the 2011 self-test database system. I suggest you go to school and find the information sharing center. There is a lot of information there.