I’d like to start a discussion of data serialization formats, in the context of Elixir. The rest of this note is a combination of personal opinions and links to useful resources; feel free to jump in with your own clues, pointers, reactions, war stories, etc. (ducking…)

edn

edn (extensible data notation) is a subset of Clojure, extracted by Rich Hickey. edn has a rich set of built-in data types, most of which are a good match for Elixir. In addition, it has a mechanism for extending this set with custom data types.

However, because edn is closely tied to Clojure, Transit (see below) may be a better choice for interoperability. For details, see edn’s GitHub page and eden’s Hex page.

JSON

JSON is a subset of JavaScript, extracted by Douglas Crockford. Although JSON shines at interoperability and standardization, it has very limited (and JavaScript-specific) data types. So, for example, I wouldn’t recommend it for cases where one needs to retain and/or transmit specific data types.

JSON is also poorly suited for generating human-readable documents. It’s possible to include comments by using data elements, but this is a hack. And, although it’s quite possible to format JSON nicely, many programmers don’t make the effort. So, a lot of JSON “in the wild” is difficult for humans to read.

JSON-LD (JavaScript Object Notation for Linked Data) is a JSON-based method of encoding linked data. Thus, it can take the place of RDF-encoding formats such as N-Triples, RDF/XML, and Turtle.

TOML

TOML is an acronym for “Tom’s Obvious, Minimal Language”, referring to its creator, Tom Preston-Werner. Although TOML has very limited data types, it excels at generating human-readable documents.

Because the top of each “section” (i.e., sub-tree) can be encoded as a path, TOML works well for encoding deeply-nested hierarchical structures:

[a.b.c.d]
  e = 42

Transit

Transit is conceptually similar to edn, in that it is an extensible format with strong data type capabilities. However, it is considerably less tied to the Clojure language. Also, its “wire format” uses JSON or MessagePack. For details, see transit_elixir’s Hex page.

YAML

YAML (“YAML Ain’t Markup Language”) is generally well suited to writing by humans, although the need for multiple levels of indentation can become an issue for deeply nested trees. Also, the syntax definition is rather large, so reading some YAML documents can be difficult. Finally, because YAML “in the wild” isn’t well standardized, interoperability can be an issue.