Posted in Interesting, Programming, Web Tech

XML, XTHML and SGML

XML is eXtensible Markup Language is a markup language developed by W3C(World Wide Web Consortium).
It defines a set of rules that are self descriptive.
It is designed to store and transport information or data which is wrapped in non-predefined tags unlike HTML which has predefined tags. The author of XML has to define the tags and document structure.

XML separates data from presentation. That is, it carries the data but does not carry any information about how to display it. The formatting and displaying is taken care of by HTML. A typical XML document is tree structure that starts with a root and branches to leaves. XML has syntax rules and any XML document that conforms to these syntax rules is said to be “Well Formed” XML document.

XHTML stands for eXtensible HyperText Markup Language. It is almost similar to HTML but more stricter than HTML. XHTML is developed by combining HTML and XML. Where is it strict?

  • XHTML DOCTYPE is mandatory
  • XHTML document must have one root element
  • <html>, <head>, <title>, and <body> are mandatory
  • XHTML elements must be in lowercase, properly nested and closed

SGML stands for Standard Generalized Markup Language is a standard for specifying a document markup language or tag set. Such a specification is called Document Type Definition(DTD). Therefore, it is not considered language in itself but a metadata.

SGML was derived from GML (Generalized Markup Language), which allowed users to work on standardized formatting styles for electronic documents. Apparently HTML and XML use SGML principles. Meaning, SGML is a superset of HTML and XML.

Posted in Open Source, Web Tech

SVG – Scalable Vector Graphics

What is SVG?

SVG is Scalable Vector Graphics. SVG is a XML based format to represent vector based graphics. It is used to draw two dimensional vector images, which support animation. SVG allows three types of graphic objects: vector graphics, raster graphics, and text

Can SVG be rendered in webpages?

Yes, SVGs can be rendered in webpages using an html tag using attributes like height and width.

Some facts about SVGs

SVG can be created using any text editor.

Since they are XML based, SVG images are searchable, indexable and can be scripted and compressed

SVG is an Open Standard

Being text format,  size is larger as compared to binary formatted graphics.

Posted in Web Tech

Web Services: the way machines communicate over network

A web service is a way of communicating or interacting machine-to-machine over a network using Internet protocol to exchange data. HTTP and XML is the basis of web services. The software system that requests data is a service requester, whereas the software system that would process the request and provide the data is a service provider.

The rules for communication describing web services and how to access them are defined in a file called WSDL, stands for Web Services Description Language. WSDL is written in XML. WSDL is a document written in XML. The document describes a Web service. It specifies the location of the service and the operations the service exposes.

A directory called UDDI (Universal Description, Discovery and Integration) defines which software system should be contacted for which type of data. Once the software system finds out which other system it should contact, it would then contact that system using a special protocol called SOAP (Simple Object Access Protocol). The service provider system would first validate the data request by referring to the WSDL file, and then process the request and send the data under the SOAP protocol.