Relation and differences between SGML, XML, HTML and XHTML What is Markup Language:

What is Markup Language? Markup language designed for processing and presentation of Text. Markup Language is human readable in comparison of other languages which have special syntax.

As ML indicates XML and HTML are markup languages.XML is generic while HTML is specific there are some specified tag and attributes that can be used in HTML  but XML can use any USER defined tag or attribute. HTML is suitable for web designing.

SGML is super set while all three (HTML, XML, XHTML) are subset with their own limitations. You can well-formed HTML is XHTL.

SGML: SGML stands for Standard Generalized Markup Language. There is no restriction at all. Any tag can open anywhere without closing of previous tag. Empty opening and closing tags are allowed. You can only attribute value without its name.

XML: A well-formed SGML with proper closing and ending of tags is called XML. Some declaration that were allowed in SGML but not allowed in XML.

1.       DATATAG

2.       OMITTAG

3.       RANK

4.       LINK…etc

HTML : HTML contains some specified tags. Well formed is not mandatory.

XHTML: will contains specified HTML tags and attributes but well form ness is mandatory.

Purpose

Xml is used to pass data from one system other. Or we used it as a database to store the data.

HTML is used to display content on web pages.

HTML may be well formed or not. But some browser need a well formed HTML to display the content. That’s why XHTML required. A website is use don many devices now like Mobile, Tab Computer and HTML has some complexity so a more strict HTML was required to reduce the overhead to read un well -formed HTML.

XHTML Rules

1.       Tag name and attributes name should be in small case.

2.       Attribute value should be properly quoted.

3.       Well-formed

4.       Non empty tag should have closing tag.