File management: logical structure

文件管理：文件的逻辑结构

逻辑结构：在用户看来,How the data inside the file is organized
物理结构：在OS看来,How the data of the file is placed in external storage（磁盘）中的

1.1 无结构文件（流式文件）

无结构文件：The internal data of the file is composed of a series of binary streams or character streams

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1.2 有结构文件（记录式文件）

有结构文件：Consists of a set of similar records.如数据库表
A record consists of multiple data items
One data item in each record is designated as a key,Used to uniquely distinguish this record

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According to whether the storage space occupied by each record is equal,Divided into fixed-length records and variable-length records
定长记录
可变长记录

1.2.1 顺序文件

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1.2.2 索引文件

Fixed-length records can be accessed randomly,That is, you can jump directly to the location you want to visit
Variable-length records cannot be accessed randomly,You cannot jump directly to the location you want to visit,You can only search backwards from the beginning,为了解决这个问题,We build an index table for the file
索引表本身是定长记录的顺序文件

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1.2.3 索引顺序文件

每个记录对应一个索引表项,Sometimes it occurs that the index table occupies more storage than the file itself,So we lead to the index order file

index table on the left,On the right is the sequence file