XML, SGML, HTML are all the same things?

[Howerski]

I know that for most of the internet application runs on XML or HTML tags but SGML has also there? Are XML, HTML and SGML are the same thing, what are main points? Are different from each other?

[Expertz]

SGML is the mother tongue, and has been used for describing thousands of different document types in many fields of human activity,from transcriptions of ancient Irish manuscripts to the technical documentation for stealth bombers, and from patients’ clinical records to musical notation.
SGML is very large and complex, however, and probably overkill for most common office desktop applications.
Wheras, XML is an abbreviated version of SGML, to make it easier to use over the Web, easier for you to define your own document types, and easier for programmers to write programs to handle them.
It omits all the complex and less-used options of SGML in return for the benefits of being easier to write applications for, easier to
understand, and more suited to delivery and interoperability over the Web. But it is still SGML, and XML files may still be processed
in the same way as any other SGML file.
And,HTML is just one of many SGML or XML applications—the one most frequently used on the Web. Technical readers may find it more useful to think of XML as being SGML– rather than HTML++.
cheers

[Michael25]

Hi,
The Extensible Markup Language (XML) is a general-purpose specification for creating custom markup languages. It is classified as an extensible language because it allows its users to define their own elements. Its primary purpose is to help information systems share structured data, particularly via the Internet, and it is used both to encode documents and to serialize data.

Standard Generalized Markup Language ( SGML) is an ISO Standard metalanguage in which one can define markup languages for documents. SGML provides an abstract syntax that can be realized in many different concrete syntaxes. For instance, although it is the norm to use angle brackets as tag delimiters in an SGML document—per the reference concrete syntax defined in the standard—it is possible to use other characters instead if a suitable concrete syntax is defined in the document's SGML Declaration.

HyperText Markup Language(HTML), is the predominant markup language for Web pages. It provides a means to describe the structure of text-based information in a document — by denoting certain text as links, headings, paragraphs, lists, and so on — and to supplement that text with interactive forms, embedded images, and other objects. HTML is written in the form of tags, surrounded by angle brackets. HTML can also describe, to some degree, the appearance and semantics of a document, and can include embedded scripting language code (such as JavaScript) which can affect the behavior of Web browsers and other HTML processors.

Hope this will hope you to understand the basic difference between the XML, HTML and SGML.