什么是Flat File

"Flat"which means it has no structure for indexing and there are usually no structural relationships between the records.

一个flat file即可以是纯文本文件(plain text file)，也可以是二进制文件(binary file)。

纯文本文件

plain text is the data (e.g. file contents) which represent only characters of readable material but not its graphical representation nor other objects (images, etc.). It may also include a limited number of characters that control simple arrangement of
text, such as line breaks or tabulation characters.

The encoding has traditionally been either ASCII, sometimes EBCDIC. Unicode-based encodings such as UTF-8 and UTF-16 are gradually replacing the older ASCII derivatives limited to 7 or 8 bit codes.

二进制文件

Binary files are usually thought of as being a sequence of bytes, which means the binary digits (bits) are grouped in eights. Binary files typically contain bytes that are intended to be interpreted as something other than text characters. Compiled computer
programs are typical examples; indeed, compiled applications are sometimes referred to, particularly by programmers, as binaries. But binary files can also mean that they contain images, sounds, compressed versions of other files, etc. — in short, any type
of file content whatsoever.

Some binary files contain headers, blocks of metadata used by a computer program to interpret the data in the file. The header often contains a signature or magic number which can identify the format. For example, a GIF file can contain multiple images, and
headers are used to identify and describe each block of image data. The leading bytes of the header would contain text like GIF87a or GIF89a that can identify the binary as a GIF file. If a binary file does not contain any headers, it may be called a flat
binary file.