What Is XML?

XML is a term that gets thrown around the publishing industry a lot, but what does it actually mean?

First, XML stands for Extensible Markup Language. XML doesn’t do anything; instead, it lets you describe what something is. It's a text format that lets you define information for computer-to-computer communication. Basically, it’s a way to let two programs that speak different languages talk to each other.

It’s best to think of XML as content without form: XML is what's in the background describing what everything is, then how it looks is determined by where that information is being used. Some familiar examples of XML-based languages include: XHTML for the web, IDML for InDesign, and ONIX for book information.

Elements

Elements are the building blocks of XML. Think of these elements like descriptors, adjectives attributed to the content. Each bit of content gets described by the element. Elements are made up of opening and closing tags, and the content goes between these tags.

Elements look like this:

<tag>content</tag>

Or, for something publishing-specific, like this:

<Title>Canadian Book Market</Title>

XML allows you to describe infinite amounts of information, but it's the receiving program that decides what to do with it. If an online store receives your file, it will take that title tag and know to post it as the title on its website. Some programs act on more of the described information than others, so to be on the safe side it’s best to provide more, rather than less, information to avoid blanks.

For example, if a book has a Canadian author, you would want to add an element that says the author is Canadian. Even if some receivers of the XML file won’t process it, some will and it will be to your advantage.

XML always sounds big and scary, but really it’s just another version of something we’ve been doing for years in publishing: marking up documents in the same way you would a manuscript.

The publishing-specific XML language for transferring information about your books is called ONIX. If you’re interested in learning more about ONIX, we have you covered in our blog post: What Is ONIX?