Re: [xml-dev] [Philosophical] What is an XML document?

> <Greeting>Hello, world!</Greeting>

This may be an encrypted message... Much more than it seems... It may mean different things on different date-times...

And 10 thousand years from now archaeologists may accidentally discover it and have different theories about its meaning...

And generally it may not be possible to say which is the message and which is the noise -- depends on the observer. What some people think is the noise may be the really interesting content for others.

Thanks,

Dimitre

On Sat, Jun 4, 2022 at 11:00 AM Roger L Costello <costello@mitre.org> wrote:

Hi Folks,

There is a file on my laptop that consists exclusively of these characters:

<Greeting>Hello, world!</Greeting>

Question: Is the file an XML document?

Answer: No, it is simply a text file.

Evidence to support my answer: I opened Notepad, dragged and dropped the file into Notepad, and subsequently Notepad displayed the file's content as a linear sequence of characters, i.e., text.

Philosophical Discussion:

An XML document is "in the eye of the beholder." That is, to Notepad my file is just text, but to Apache Xerces my file has a structure consistent with the XML specification and therefore -- to Xerces -- it is an XML document.

In order for a file to be considered an XML document, two things must align:

1. The application assessing the file must have internalized the grammar rules specified in the XML specification.

2. The application must process the file to determine that the file has a structure consistent with the grammar rules.

Only if 1 and 2 are satisfied may the application pronounce "Yes, this is an XML document."

Let's dig a bit deeper...

Clearly the following is a linear sequence of characters:

<Greeting>Hello, world!</Greeting>

It only becomes an XML document when an XML-aware application has processed it (assessed it) and determined compliance with the XML grammar. The most common method of determining if an input string conforms to a grammar is to lexically analyze the string into tokens and then see if the tokens matches a specified grammar; along the way an in-memory "parse tree" is created. If we successfully create a complete parse tree, then we have an XML document. If we have an XML document, then we have successfully created a complete parse tree. An XML document is a parse tree.

No one would deny that a parse tree is a "data structure." Therefore an XML document is a data structure.

Do you agree with my line of reasoning? Where does my logic go astray?

/Roger

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Cheers,

Dimitre Novatchev

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