Understanding YAML

So far, we've looked at CSV, XML and JSON as data on the web solutions, all of which are text-based and all of which are fairly easy to read. In this chapter, we'll examine another entry in the data on the web sweepstakes, one that relies on visual spacing to provide structure. I am, of course, referring to YAML. The YAML does not, as some would think, stand for Yet Another Markup Language. Rather, it's a recursive acronym that's short for, YAML Ain't Markup Language because so little markup is actually used.

It was first proposed in 2001 and created by the wonderfully named Ingy dot Net, along with partners Clark Evans and Oren Ben-Kiki. You can find the latest version as well as reference material at the yaml.org site. Don't be taken aback by the purely textual page, the page itself is written in YAML format. The creators of YAML refer to it as a Human-readable data serialization standard. Which, ironically, is somewhat less human understandable than YAML code itself.

Here, we're seeing a user with a first name, last name, and state specified. Notice the complete lack of quotes and how quickly you can grasp what's going on. YAML unlike many markup languages which are white space agnostic, uses positioning for structure and simple characters as delimiters. Specifically, structure is determined by indentation using spaces, not tabs. That's important. The name value pairs, or as they are called in YAML, key value pairs, are separated by a colon.

As noted before, strings don't require quotes. Although in some cases, like a zip code, you might want to use them to distinguish your string from a number. To indicate a list item, you use a hyphen, which just coincidentally is how I write out my list by hand so it makes a lot of sense to me. The indented structure, because it doesn't use any delimiters that you have to escape, is great for including other code like HTML, XML, or JSON and it can all be included as a YAML data object.

Because it's purely a representation of data and there are no executables, security for YAML is pretty high, although I understand certain parsers have to be careful. Such parsers are available in all major languages including C++, Java, JavaScript, .NET, Perl, PHP, Python, Ruby, and many others. Like all markup languages, the only way you really understand what YAML is all about is to start using it. So, let's get to it beginning in the next lesson.