XML vs HTML
XML stands for EXtensible Markup Language. It is defined in the XML 1.0 specification, which is developed by the W3C (World Wide Web Consortium). XML provides a standard way, which is also simple, to encode data and text such that the content could be exchanged across driver hardware, operating systems and applications with little human intervention. HyperText Markup Language, widely known as HTML is also a leading markup language for web pages. HTML is the basic building block of web pages. Web browser reads the HTML document and composes them into visual or audible web pages.
XML
XML is a markup language that is used to transfer data and text between driver hardware, operating systems and applications with little human intervention. XML provides tags, attributes and element structures that can be used to provide context information. This context information can be used to decode the meaning of the content. This makes it possible to develop efficient search engines and perform data mining on the data. Furthermore, traditional relational databases are suitable as XML data because they could be organized in rows and columns but XML provides less support for data with rich content such as audio, video, complex documents, etc. XML databases store data in a structured, hierarchical form which allows queries to be processed more efficiently. XML tags are not predefined and the users can define new tags and document structures. Also, new internet languages such as RSS, Atom, SOAP, and XHTM were created using XML.
HTML
HTML as mentioned earlier is a markup language that has a set of mark up tags. HTML markup tags, which are usually called HTML tags are used to describe web pages. Typical HTML documents contain HTML tags as well as plain text required for the content of web pages. HTML tags could be identified easily in a HTML document since they are surrounded by angle brackets (e.g. <HTML>). HTML tags are typically inserted in to a document in pairs, where the first tag is the start tag (e.g. <b>) and the second tag is the end tag (e.g. </b>). The task of a web browser (e.g. Internet Explorer, Firefox, etc.) is to read a HTML document and display it as a web page. The browser uses the HTML tags to interpret the content of the page, but the HTML tags themselves are not displayed by the browser. HTML pages can embed images, objects and scripts written in languages like JavaScript. Furthermore, HTML can be used to create interactive forms.
Difference between XML and HTML
Even though, XML and HTML are both markup languages, there are some fundamental differences between them. HTML mainly consists of tags that define the appearance of the content, while XML tags generally define the structure and the content of data (and the actual appearance is defined by an associated style sheet). Secondly, XML is extensible, since the XML tags can be defined by the user for a specific application, while HTML tags are defined by W3C.