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All Rights Reserved. W3Schools is Powered by W3. Depending on how elaborate rules you allow in your grammar, differently sophisticated machines are required to prove that a given word can actually be produced by the grammar.
The example given above is a regular grammar, which is the most simple and least powerful. The next powerful class of grammars are called context-free. These grammars are also very simple to verify. XML unless I'm overlooking some obscure feature I'm not aware of can be described by a context-free grammar. The classification of grammars forms the Chomsky Hierarchy of grammars and therefore languages. That is, there exists a machine that, given a word that actually belongs to the language, derives a proof that it can be produced by the grammar within finite time, and will never output a wrong proof.
Such a machine is called a verifier. Note that the machine may never halt when given a word that doesn't actually belong to the language. Clearly, we want our programming languages be described by less powerful grammars for the benefit of being able to reject invalid programs within finite time.
Schemata are an addition to XML that allow refining the set of well-formed documents. A well-formed document that follows a certain schema is called valid according to that schema. For example, the string. Schema validation can also be done by an algorithm that is guaranteed to halt after finite amount of steps for every input. Such a program is called a validator or a validating parser. Schemata are defined by so-called scema definition languages , which are a way to formally define grammars.
You can define a set of rules that gives XML documents an interpretation as descriptions of computer programs. More generally, you can serialize the abstract syntax tree of almost any programming language quite naturally into XML, if this is what you want. In computer science, formal language is just a set of strings, usually infinite and often described using rules two common versions of those rules are regular expressions and formal grammars.
Note that this means that all a language needs is syntax , language doesn't need to describe what each valid string means that's called semantics. Now, this means that programming languages are formal languages that also have semantics, which describes some computation.
And for example XHTML is a formal language, whose semantics describe roughly and informally how a hypertext document looks and behaves. Technically, binary formats are also languages, but they're not called that way. The term "language" is reserved for human-readable formats.
XML is a meta-language. You use it to define specific languages. Languages never do anything, they just allow us to express things. Also, it is not true that XML is a "storage language". Just the opposite, in fact. You can store XML docs however you please. XML is better thought of as a transfer language.
If you don't think XML "does" anything, you'll have to explain how it is that many systems e. It's a lamentable abuse of XML, but it exists in the wild, and that just one of many examples. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Why is XML called a "language" exactly? Ask Question.
Asked 5 years, 7 months ago. Active 5 years, 7 months ago. Viewed 25k times. I've been wondering why XML has an L in its name. I'm asking about the L! Improve this question. Mr Lister. Mr Lister Mr Lister 1, 3 3 gold badges 12 12 silver badges 18 18 bronze badges.
On what do you base your requirement that a language has to "do" something? I don't see that in any of the definitions at dictionary. Just like Swahili is only understood if both understand it. Or a medical journal article is understood if the reader understands that part of the language. It's no different. And people make up the definitions. Markup language is a common term en.
MrLister: "Those are human languages, not computer languages" A language is a language. At its most extreme, even English requires contextual information which dialect is being used to understand unambiguously. Doesn't stop it from being a language.
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