Xml xsl dtd schema html

XML: xetensible Markup Language Extensible Markup Language

SGML: Standard Generalized Markup langauage standard general markup language. It is powerful and can define the language of the markup language.

XML is a simplified subset of SGML, reflecting the relationship between data and data.

The current XML versions are 1.0 and xml1.1, and the most used is 1.0.

 

Is XML an extension of HTML ??

The full name of HTML is hypertext markup language (Hypertext Markup Language). In fact, HTML and XML are at different levels in the markup language.

HTML has a standard tag. If a custom tag is used, it will not be recognized by the browser.

XML does not have a standard markup language and can be created at Will (the metalanguage of the Markup Language)

 

Relationship between sgml html and XML

SGML appeared before the Web. It is a metalanguage that defines the markup language.

HTML and XML have evolved from SGML. html is a descriptive language defined in SGML and is an application of SGML. Its DTD is defined as a standard. XML is a subset of SGML. To be precise, XML is still SGML.

HTML cannot define applications. XML can define new applications.

 

XML describe the thing itself

XSL modifies XML and allows it to install the specified format for display. Therefore, XML achieves data and display separation.

DTD and Schema are used to restrict legal tags in XML. If XML does not have any restrictions, tags can be defined at will. After adding DTD or schema, you can only use corresponding tags, it facilitates cross-platform data and cross-language interaction. DTD is a previous version, such as 2.3dtd, 2.2dtd, and 2.1dtd. It is named 2.4xsd and 2.5xsd from 2.4.

In javaee development, it is necessary to clarify the DTD and XSD, such as The namespace and XML restrictions of Web. xml and struts2.xml.