I would say that a text file is one which, when sequentially read, has is a simple transformation from the bytes to a sequence of characters in one or more character repertoires (lists), fully consuming all bytes with none remaining, except any file-termination codes. This transformation may be direct mapping using the values of the bytes, or may involve mapping sequences of bytes to some other number (e.g. UTF-8), or may involve a simple state machine (e.g. ISO 2022), for example, (but surely nothing requiring a stack or random access.) The result and initial objective of parsing the file is a single sequence of characters.I would say that a binary file, when used in distinction to "text file", is one which uses potentially more complex transformations, where the result and initial objective of parsing the file will be a data structure or event stream.
So a ZIP file containing an uncompressed XML file is not a text file, because there are some bytes that are not intended to map to characters. But a file with a single DNA sequence as a packed string probably counts as a text file.
{You might say that therefore a file containing artificial languages like markup is a text file that is also like a binary file (in that you end up with a data structure or event stream.)}Text and binary are also names used to represent different modes in some applications: e.g. in FTP a text file may have its newlines replaced with platform specific newlines (a la text/* MIME type) and perhaps even be transcoded, while a binary file will be kept byte-for-byte intact (a la application/* MIME type.) This usage for modes should not cloud the usage relating to files.
So the test of a text file is "can I read it?" but "is it intended to be a sequence of characters from some repertoire with a 'simple' O(n) sequential mapping from the bytes"?
Something like that.Cheers
RickOn Mon, Nov 25, 2013 at 1:25 AM, Costello, Roger L. <costello@mitre.org> wrote:
Hi Folks,
Distinguishing "text" versus "binary" is important.
On October 30 we had a discussion titled, "Is the binary file format dead?"
During that discussion John Cowan made an excellent distinction between binary and text files. I thought it would be useful to summarize the distinction.
The universe of computer files falls into two categories:
1. Binary files
2. Text files
By convention we normally restrict "binary" to files which are not interpretable as streams of characters. [John Cowan]
The word "text" is applied to files which are interpretable as streams of characters.
Of course any text file is also a binary file, since the class of text files is obtained from the class of binary files by applying restrictions. But it would be confusing to call a text file a binary file; it would be like calling a cat a mammal: correct but imprecise.
/Roger
