Hierarchy is an idea and an idea.

Hierarchy is an idea and an idea.
The database has a three-tier mode and two-tier image. This layer is designed as needed and has certain functions for each layer. This design concept of "performing their jobs" is not only used in databases, but also a typical ISO 7-layer model with hierarchical functions on the network. This "hierarchy" is an idea. When people face a problem, they always need to find a simple and reliable solution. The idea of "layering" guides people to separate this problem from the same angle, form their respective layers, and then ensure the collaboration and mutual connection between each layer through a "Connection Mechanism. Next we will use this three-tier model to introduce the "layering" idea.Logical Model:To design a database system, you first need to have a general understanding of the system from the perspective of user requirements, which generates a summary model, then this rough model is converted into a logic concept model in computer technology, which generates a logic model (which can be understood as follows, A model is a summary model designed by a person who does not understand computers. A more professional model is a logical model .)
It solves the Global Logical Structure of databases implemented by computers.
External Model:If the database system needs to be used by programmers, in many cases programmers do not need all the data, so they need to design a small model that is convenient for programmers to use. This is an external model.
Solved the DB point of view from the user's perspective.
Internal Model:The bottom layer of the database system, that is, the logic thinking, should consider how to organize data storage on computer hardware. In this way, a model is proposed, which is the internal model.
This solution solves the hardware structure of DB.Contact:Later, in Computer Implementation, various models work collaboratively through the image mechanism.
The fundamental source of stratified thinking is abstraction. Database hierarchy is different in degree of data abstraction, so different models are created based on different levels of abstraction. Various layers collaborate to complete a huge amount of tasks in the system.
Is Stratified Teaching a teaching mode?

Stratified Teaching Mode Seminar [1] 2. it is conducive to the improvement of classroom efficiency. First of all, it is a new teaching method for teachers to level-by-level teaching at different layers. It is necessary to comprehensively strengthen teaching management and boldly carry out teaching management.

How to layer paragraphs

Section Division Method
Segmentation refers to the part in which the author combines the content in a certain way to express the central idea, that is, the logical Section, also known as the meaningful section.
There is no absolute standard for segmentation, but there is a basic requirement: it can reflect the author's ideas and show the context of the subject of the text. This "Train of Thought" and "context" refers to the conception sequence and writing steps of the author during writing. How can students correctly grasp the conception sequence and writing steps of the author while learning the text? How can we draw a paragraph accurately? First, you must master the segmentation steps, and then select the correct segmentation method.
I. Segmentation steps
The segmented steps can be summarized into four words: "Read, think, query ." "Read" refers to reading the full text, clarifying the author's ideas and presenting the context of the text, which is the key to segmentation. "Thinking" refers to the main content of each natural section; "returning" refers to merging the natural sections with one or more closely related content to make them a righteous section; "check" is to first associate the meaning of each paragraph with the full text center to check whether it is consistent, and then link the meaning of each paragraph to see whether it constitutes a rigorous whole.
Ii. Segmentation
The vertical segmentation method and horizontal segmentation method are used for segmentation.
To master these two methods, we must first understand the concepts of vertical structure and horizontal structure. The so-called vertical structure refers to the article structure arranged in the order of occurrence and development of things. Narrative text (Note) mostly belongs to the vertical structure. The "horizontal structure" refers to the article structure that divides the content to be recorded and explained into several horizontal planes and is carried out in parallel from several aspects. Plain text is usually in this structure.
(1) the vertical segmentation method follows the vertical structure segmentation method, which is called the vertical segmentation method. It generally includes the following two types:
1. segmented by the sequence of things, which is common in narrative.
2. segmented by time sequence.
In general, the development of its events is clearly marked by the time sequence, or by the location conversion sequence. Therefore, it is necessary to grasp the time term and azimuth term of the text during segmentation as an important basis to divide the meaning section. Arrange the narrative of the materials in chronological order. You can use the time word capture method to segment the documents. The occurrence and development of events often come along with the passage of time. Therefore, when segmentation is used, we need to determine which method is the most important and select an appropriate method.
(2) The horizontal segmentation method is called the horizontal segmentation method according to the "horizontal structure. There are also two types:
1. segmentation is classified by the nature of things. This classification segmentation method is mostly used for plain text.
2. segment by spatial location conversion. This type of segmentation method is mostly used to record the narration of people in different locations.
In addition to the vertical segmentation method and the horizontal segmentation method, there are also segmented by character appearance order and by the author's narrative method. Segmentation By Character appearance sequence is generally applicable to scripts.
In some texts, there is often a transitional section linking up and down. When the section is segmented, will it belong to the upper section or the lower section? Generally, you can consider the following two aspects:
1. Argumentative transitional section, based on the focus of its discussion, consider its local ownership.
2. the narrative transition section considers its upper and lower attribution based on its foothold in the narrative, which is generally divided below.
Of course, the method for dividing paragraphs is not just the one mentioned above, but is not listed here.
It should be noted that paragraph division in an article is often more than one method.
Paragraph Division should prevent the following situations: one is chaotic thinking, and the Division standards from beginning to end are inconsistent; the other is not paying attention to the ownership of the transitional sentence between paragraphs; there is also a formula for segmentation. No matter what kind of articles, all three sections will lead to incorrect segmentation.
It is not difficult to segment an article. As long as you think carefully, follow the rules, and practice more, you will be able to divide it correctly.

Summary
The principle of induction section is an important means to understand the content of the text and grasp the author's ideas. It is also a prerequisite to grasp the main content of the text and summarize the central idea.
The general purpose of an induction section is to check whether students understand this section. It is an important symbol of understanding the main content of this section. It is the basis for reading a text and an important training for cultivating students' analytical generalization ability.
Induction paragraphs have three requirements: one is to reflect the main content of the paragraph; the other is simple and clear syntax, and the other is to reflect the main content of the article. Among the three requirements, the first is the most basic. Only by grasping the main content of a paragraph can we make it concise in terms of language expression. By grasping the main content of a paragraph, each paragraph can become the outline of the article.