XML Language – Understanding Why XML is Called a Language

language-designlanguagesmarkupxml

I've been wondering why XML has an L in its name.

By itself, XML doesn't "do" anything. It's just a data storage format, not a language! Languages "do" things.

The way you get XML to "do" stuff, to turn it into a language proper, is to add xmlns attributes to its root element. Only then does it tell its environment what it's about.
One example is XHTML. It's active, it has links, hypertext, styles etc, all triggered by the xmlns. Without that, an XHTML file is just a bunch of data in markup nodes.

So why then is XML called a language? It doesn't describe anything, it doesn't interpret, it just is.

Edit: Maybe my question should have been broader. Since the answer is currently "because XML was named after SGML, which was named after GML, etc" the question should have been, why are markup languages (like XML) called languages?

Oh, and WRT the close votes: no, I'm not asking about the X. I'm asking about the L!

Best Answer

The real answer is XML has an L in the name because a guy named Raymond Lorie was among the designers of the first "markup language" at IBM in the 1970'ies. The developers had to find a name for the language so they chose GML because it was the initials of the three developers (Goldfarb, Mosher and Lorie). They then created the backronym Generalized Markup Language.

This later became standardized as SGML (Standardized General Markup Language), and when XML was created, the developers wanted to retain the ML-postfix to indicate the family relationship to SGML, and they added the X in front because they thought it looked cool. (Even though it doesn't actually make sense - XML is a meta language which allows you to define extensible languages, but XML is not really extensible itself.)

As for your second question if XML can legitimately be called a language:

Any structured textual (or even binary) format which can be processed computationally can be called a language. A language doesn't "do" anything as such, but some software might process input in the language and "do" something based on it.

You note that XML is a "storage format" which is true, but a textual storage format can be called a language, these term are not mutually exclusive.

Programming languages are a subset of languages. E.g. HTML and CSS are languages but not programming languages, while JavaScript is a real programming language. That said, there is no formal definition of programming language either, and there is a large grey zone of languages which could be called either data formats or programming languages depending on your point of view.

Given this, XML is clearly a language. just not a programming language - though it can be used to define programming languages like XSLT.

Your point about namespaces is irrelevant. Namespaces are an optional feature of XML and do not change the semantics of an XML vocabulary. It is just needed to disambiguate element names if the format may contain multiple vocabularies.

Edit: reinierpost pointed out that you might have meant something different with the question than what I understood. Maybe you meant that specific vocabularies like XHTML, RSS, XSLT etc. are languages because they associate elements and attributes with particular semantics, but the XML standard itself does not define any semantics for specific elements and attributes, so it does not feel like a "real language".

My answer to this would be that XML does define both syntax and semantics, it just defines it at a different level. For example it defines the syntax of elements and attributes and rules about how to process them. XML is a "metalanguage" which is still a kind of language (just like metadata is still data!). As an example EBNF is also clearly a language, but its purpose is to define the syntax of other languages, so it is also a metalanguage.

Related Solutions

XML – Why XML is Not Called EML

I took a very pleasant tour through W3C, Google, and Wikipedia and finally found the answer: an annotated XML spec where we find an excerpt of an email from the inventor of the name, James Clark, an email from chairman Jon Bosak who suggested to use the X letter, and some other ideas for names and the final votes:

Votes | Acronym | Full Name
------+---------+--------------------
5     | XML     | Extensible Markup Language
4     | MAGMA   | Minimal Architecture for Generalized Markup Applications
3     | SLIM    | Structured Language for Internet Markup
1     | MGML    | Minimal Generalized Markup Language

This is Jon Bosak's reply to James Clark's suggestion to name it "Extensible Markup Language" and gave birth to the acronym:

In my opinion, the U-combinations won't fly, but if we allow "X" to stand for "extensible", then I could live with (and even come to love) XML as an acronym for "extensible markup language", and I hereby now throw it into the list of current proposals.

^{(Emphasis mine)}

Some bonus - from some old reports of the XML Special Interest Group that I found while looking for some original quote that could answer the question:

M.15 Should the spec refer to XML as "The Extensible Markup Language" or as "Extensible Markup Language" without a definite article (e.g. in the first sentence)?

The WG elected to give no guidance to the editors on this issue (in the full expectation that the result would depend on which editor touched the file last).

Rationale: after several minutes' discussion and increasing hilarity, no consensus had been reached, but the end of the allotted time for the conference call had.

HTML vs XML vs XHTML – Key Differences and Relations

HTML and XML are both markup languages (hence the *ML). XML is a generic markup language suitable for representing arbitrary data, while HTML is a specific markup language suitable only for representing web pages.

HTML and XHTML are both subsets only of SGML, except that XHTML has additional specifications so that it also validates as XML. Think of XML as XHTML's influential godfather.

Because of this relationship to SGML across all 3 of these languages, there are a lot of similarities, but they are all considered different languages. However, much of what defines these languages is their restrictions on SGML.

HTML restricts SGML by defining a list of tags that are allowed to be used.
XML restricts SGML by not allowing unclosed or empty start and end tags, and forces attributes to be explicit. XML also has a large number of additional restrictions that are not found in SGML.
XHTML restricts SGML with the tags from HTML (with some exclusions, such as frameset, et al), and with the tag and entity restrictions from XML.

You may find this document helpful, although the technical terms may be hard to digest. http://www.w3.org/TR/NOTE-sgml-xml-971215

XML is not a metalanguage for defining markup languages. Really that's just SGML. XML is simply a data formatting markup language. Your quoted source is using technical terms imprecisely, which is why they are confusing.

Purposes

XML is for defining your own data format. If you wish to pass data between two systems, XML is often the way to do it.

If, for example, you needed to pass a sales order from your website to your billing system, you could create this XML payload:

<order id="12345">
    <name>John Doe</name>
    <item id="443">Adult Diapers</item>
</order>

Your website would then send that XML to your billing system, which could then parse the data from that XML.

XHTML and HTML are obviously just for web pages. XHTML's primary purpose is to remove a lot of the ambiguity that we had in previous years (decades) of web development. Back in the late 90s when I started, we were using HTML 3.2 which allowed for seriously sloppy code. HTML 4+ and XHTML try to remedy that by either strongly suggesting or enforcing explicit closing tags, explicit attributes, and disallowed tags, which makes it easier on both browsers and humans, and avoids unexpected differences in behaviour cross-browser.

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XML – Why XML is Not Called EML

HTML vs XML vs XHTML – Key Differences and Relations

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