PHP Infinitus Classification Principle

Concept

PHP Infinite Classification Principle A more vivid metaphor is like a tree. This tree It has its own roots, then the trunk, branches and leaves. The further forward, the denser it becomes. This is the same as classification. The further you go down, the more columns there are for classification, just like the pre-installed PCs that everyone uses. For the WINDOWS operating system, you can try to create a new folder in a folder and then create a new one in this new folder, and keep going. You can understand what infinite level is.

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##Principle

First of all, we assume that there is such a three-level classification, News→PHP News→PHP6.0 is out. If we want to find the news "PHP 6.0 is out", we can click on the news first, and then click on the PHP news to find it out. That is, we can search down level by level through the grandfather class, and in turn we can As long as you know the parent class of a subclass, you can find it. In this way, when we design the database, we can design one more field of parent class ID to achieve unlimited classification. The parent class ID in the database is particularly important. Next, we can use recursive and iterative methods to complete infinite classification. Classification production. For a deeper understanding, we can use the metaphor of a family tree and a descendant tree.

The family tree is one of the manifestations of Infinitus classification, and the other is the descendant tree. The difference can also be seen from the Chinese meaning.

Genealogy, it is now popular in many places to build a family tree. How to build a family tree is to find an ancestor for yourself, find it from generation to generation, and form a system. What is compiled in this way is called a family tree. A family tree is similar, starting from a node and looking upwards for its parent node, and then looking for the parent node's parent node until it cannot be found. According to this search, a tree-like structure formed is called a family tree.

The descendant tree is the opposite. The descendant tree is similar to the genetic diagram in the biology book. It starts from a node and searches for its child nodes, and then searches for the child nodes of the child node until the search is completed. The tree structure formed in this way is called a descendant tree.

Recursive flow chart

Iterative flow chart

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