What is XML?

Defining XML

To understand what an XML format and its code are, it’s important to take a closer look at its history. The markup language was created by the World Wide Web Consortium (W3C) in 1996. The W3’s goal was to create a language that could help define document types as well as offer the ability to create your tags (unlike HTML, its close relation – see below). The resulting markup language type enables you to tag how data is defined on the page before being shared with another system as an XML file.

So long as both systems speak the same XML language – i.e., use tags they can both interpret – then both can ‘understand’ the XML file format. When XML is deployed correctly, this ensures any data file can be stored, transmitted, and then used, reproducing the same data and its structure every single time it is accessed.

Do bear in mind that XML documents only store any data within a file. It cannot do anything with the file. Instead, software is required to carry out basic functionality such as sending or receiving the data.

Harnessing the Hierarchy

Importantly, the above sample shows the hierarchical nature of XML documents. For instance:

• You create the root element. In this case, the root element is  .
• Contained within this root element are all other elements – known as ‘child elements’.
• There are three child elements in the above example – the three different tags.
• Within these are further child elements including  and .

The tags used show what each data type is with the plain text acting as the data itself. Also, notice how the content is indented. This is not to help systems process the XML file but to aid humans scan through the XML file and its hierarchical order more easily so any errors or oversights can be spotted and resolved.

Creating an XML document or editing one doesn’t require a costly specialist application either. After all, XML is plain text so a text editor, online XML editor, or a web browser can be used.

What is XML Schema?

A schema acts as a ‘definition’ of the XML document. This means it profiles key rules and limits for how the XML file is structured as well as controls for content and data types – and crucially, how they interact with one another within the document. Combined, this ensures that the XML’s data integrity is protected at all times, even when being processed between different apps, and even systems.

The two key schema languages are Document Type Definition (DTD) and XML Schema Definition (XSD). XSD is the most used language in XML documents because of its rich feature sets, powerful data typing capabilities, and more. However, some sectors require specific functionality from their schemas that XSD is not optimized for.

For instance, industries that leverage computer graphics-related data deploy the Scale Vector Graphics (SVG) schema to write their XML files. The SVG schema is ideal for web design/development, user interfaces, and other applications as it was specifically created for the description of two-dimensional vector graphics. Other specialist schema languages include Mathematical Markup Language (MathML) and Chemical Markup Language (CML), their specific uses are self-explanatory.

What is XML syntax?

If XML schemas such as XSD are all about detailed specs for the XML document to ensure it is valid, XML syntax offers a set of rules for managing and governing the overall structure of an XML file. For example, XML syntax can cover text content such as self-closing elements (a single piece of information with no need for additional content) or an XML declaration (used at the beginning of the document to profile key information such as character coding), and which XML version the doc is using.

What are the different versions of XML?

XML has been around since 1998 when 1.0 was published by the W3C. XML 1.1 touched down in 2004 to address several existing issues as well as introduce new features. While no new version has been launched since 2004, a Second Edition of 1.1 (2006) and a Third Edition (2017) were introduced to boost XML’s stability.

What are the differences between XML vs HTML?

If you are familiar with HTML, the way XML files deploy tagging will look very familiar – but there are two key differences between the markup languages:

HTML is used to show how data should be presented onscreen with a web browser able to understand it. The XML file format is used to show how the data should be structured and look with an application able to process and present the data correctly.

Software, though, can only do this if it has been programmed to understand the XML tags used in the XML file format. This introduces XML’s key strength compared to HTML. The latter has a fixed list of tags that can be used. However, XML is extensible, allowing you to create as many of your unique tags as you want to manage your data sets.

Crucially, XML documents can be utilized – or offer a supporting role – in many different areas of an IT strategy. From data processing and going cloud-native to block storage and building bots, XML’s versatility and flexibility make it an essential tool for any business committed to using the full potential of all enterprise assets.

What are the disadvantages of XML?

One of XML’s great strengths is its exceptional versatility, enabling users to tag their data however they wish via custom tagging. Ironically, this also represents XML’s Achilles Heel: The need for the XML file’s receiver – such as an application – to understand each unique tag or set of rules. After all, what’s the point of a perfectly tagged XML file if it can’t be read, interpreted, and acted on by the applications receiving it?

To overcome this issue, XML files can be supported by an XML stylesheet (XSLT), which can be shared between the two parties. These can be utilized to create a standardized XML format, language, and rules between the entities so all information and characters can be shared and read effortlessly without anything being ‘lost in translation’.

To minimize this issue further, sectors such as finance and e-commerce have created XML dictionaries to ensure all XML files can be deciphered and read by defining set rules. These seek to bring uniformity to tag definitions and can be embedded in XML documents to remove any potential compatibility issues at source.