What Is XML Schema and What You Need to Know

 XML Schema: The Basics XML basically stands for "Extensible Markup Language". It's main job is to allow for the transportation and storage of data, it is fundamentally different to HTML because it serves a different purpose. HTML is principally about the displaying of information whereas XML is as stated above, about carrying information.

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So why has XML come about? Quite simply in the early days of the world wide web, websites were a lot simpler animal with most websites comprising of static html pages and typically viewed on fixed PC's. But as time went on this changed dramatically with the introduction of hand held devices, laptops, wireless technology and other devices.

The problem arises in the difference in platforms and browsers of standard PCs to wireless types, they are not particularly compatible with many elements of the standard HTML language and as a result, people viewing straight HTML webpages on wireless devices found sections if not whole parts the websites they were looking at, invisible or missing.

The solution was found quite quickly by programmers who created a standard language that would be compatible for both wireless and non wireless platforms and so allowed web pages to be viewed in the same way. This standard language was called XML and it was a great way to define data and allow data to be viewed on any machine or browser in much the same way. This evolution soon lead to XHTML and XSL specifications being developed which allowed XML files to be turned into webpages by defining style and structure, again this meant you could view a webpage as intended by the author the same on any browser or device.

So What's An XML Schema Then? Put simply an XML schema is a set of rules or specification if you like, that a programmer would use to describe the structure of an XML document. For example with a database schema will describe the data that can be contained in a database (table structure, data types, etc.) An XML Schema is much the same for an XML document, it is effectively a rule set.

Prior to an XML Schema, the standard was set by something called DTD or Document Type Definition, which programmers would use to structure their XML documents, however the XML Schema standard is now universally seen as the replacement for DTD. The XML Schema was first created by Microsoft and then later adopted by the W3, it has evolved over the years and is now controlled by the W3C under the XDS standard, Microsoft's standard was the XDR but this is now defunct and the XDS is the defacto standard for describing XML documents.

So what does an XML Schema do? Put simply it allows data to be communicated in a format that is universal and so it allows a sender to transport data to the recipient and for the recipient to understand the data i.e. interpret the data using a set standard that is universal. For example, there are many formats to display the date and time, some put the month first, some the year. The XML Schema for date requires that all dates be in YYYY-MM-DD format.

An XML Schema has many data types that are built in for the purposes of defining data. This is achieved through the use of attributes. For example, string, decimal, Boolean, integer, date and time are all examples of XML schemas attributes.