Why do directory structures have to exist in a file system?

The most fundamental reason for the directory structure is that files based on the same filename cannot co-exist in one directory, otherwise, the computer would not be able to distinguish these files when addressing them by filename. Other than that, the biggest advantage of the directory structure is to categorize the files. But, if we consider the scenario in life, a directory is equivalent to a box or a shelf, in the case of having two books with the same title, that is, two books with the same name, can only one book be put in a box? Books with the same title are placed together on a shelf in a library, when has it ever been stipulated that the books placed on a shelf cannot have the same title (name)?

No, it was not a must in a file system, there was an operating system called CP/M that had no directory in its file system, it was popular in the 70s to 80 ages of last century. After that, all file systems were built based on one directory structure which is also the only structure type that exists in a file system (for example, all files in C disk are under the root directory of C or its subdirectories, so they’re all in one directory), and this situation has lasted for about 50 years, all applications and database software developed base on it, until now nearly no new space to develop anymore, what if the only one directory structure being replaced by multiple graph structures which have many kinds of file structures including directory? Would this open a new window for the file system and operating system development?

In this paper, first, a non-directory file system scheme is presented that allows files with the same filename to coexist in a directory, and then a method for building file system structures using tags, including directories and other types so that files can be easily classified into one or more multitype structures, is presented for file systems that allow tags, whether directories or non-directories. Finally, by combining these two chapters, a new file system is proposed with new file manager interfaces and new methods for file manipulation.

For details of the paper, please visit:  https://docs.google.com/document/d/1iw1QNMpeCYAimWHWxTmLqNlSG0yTEY10oR7VcGNUWNY/edit?usp=sharing