YAML and JSON
YAML was invented in April of 2001. Well it started then... It's still being invented at some levels. I happened to be one of the primary 3 guys who spent several years and countless email hours inventing it.
Technically YAML and JSON aren't even related. And just for the record neither are YAML and XML. Wikipedia pretty muchs gets it right in the first sentence definition for each of these:
- XML is a ... markup language.
- YAML is a ... data serialization format.
- JSON is a ... data interchange format.
NOTE: I'm not talking about XML from here on. This post is about YAML and JSON.
One day, early on in JSON's existence, someone noticed that JSON is a pure subset of YAML. Well this wasn't completely true, but enough so that both camps adjusted their specs to make it true. The whole concept is freaky because YAML showed up years before. My only rationale is that YAML was so ambitious. We tried to make it look like everything. And we got really lucky with JSON. Anyway it's all history at this point...
So what are the differences then? In a nutshell JSON handles all the common cases for turning data into text and back into data. YAML handles all the cases so it can be a serious data serialization language. This makes JSON almost trivial to implement, and YAML almost impossible. So even though YAML was first, JSON caught on like wildfire. Since JSON is a subset, it really doesn't have anything YAML doesn't. Except a cool logo. YAML has no logo!
Here's a list of what YAML does have:
- YAML has two ways to show collections (hashes and arrays): (Python-like) indentation and (JSON-like) braces.
- YAML has many scalar quoting styles. Unquoted, double quoted, single quoted, literal block, and flow block. JSON uses double quotes for all strings.
- YAML has data typing. It uses a taguri based system for explicit typing, and also supports implicit typing. JSON supports only String, Number and Boolean scalar types.
- YAML supports multiple references to identical nodes, including circular references. JSON does not.
- In YAML, a hash (mapping) key can be any node (including another hash, array or aliased node reference). In JSON a key is always a String. It should be noted that YAML goes beyond the capabilities of most programming languages in this regard. Only Ruby has full object key support, afaik.
- YAML allows a "stream" to consist of multiple "documents", or top-level nodes. These can be any node of course. In JSON you can only have one top level object, and it must be a hash or an array (not just a scalar).
I think all of these things make YAML a great serialization format, and avoiding all these things make JSON a great data exchange format.