1. Technology
You can opt-out at any time. Please refer to our privacy policy for contact information.

Structure of a JSON Document


JSON (JavaScript Object Notation) is a data serialization format for communicating between applications. It's a text format that features a lightweight syntax and closely mirrors the common data structures in modern programming languages such as Ruby's Arrays and Hashes. JSON can be used in a variety of places, but its most common use is to be consumed from a web API.

The format of a JSON document is quite simple. There are only two organizational structures: an ordered list (which will be mapped to a Ruby Array) and a key/value list (mapped to a Ruby Hash). The syntax is also simple, using only the brace characters { and }, bracket characters [ and ], delimiters , and : and the double-quote character ".

In addition to these two data structures, JSON provides a small amount of data types.

  • Strings - A quotes string in double quotes.
  • Numbers - An unquoted positive or negative number, with scientific notation supported.
  • Boolean values - The unquoted strings true and false.
  • Null value - The unquoted string null, the equivalent of nil in Ruby.

Below is an example JSON document describing the employees of a company. The top-level structure of the document is a Hash in brackets { and }. There are a few key/value pairs describing the top positions, and key/value pairs with Arrays as the values describing the employees in various departments.

  "CEO": "William Hummel",
  "CFO": "Carlos Work",
  "Human Resources": [
    "Inez Rockwell",
    "Kay Mcginn",
    "Larry Conn",
    "Bessie Wolfe"

  "Research and Development": [
    "Norman Reece",
    "Betty Prosser",
    "Jeffrey Barclay"

The top-level element of the document is a Hash. It has two key/value pairs, one for the CEO and one for the CFO. The values for both of these keys are simple strings. The next two key/value pairs hold Arrays. The keys are strings as before, but the values are Arrays of strings enclosed in brackets [ and ].

While this was a simple example, that just goes to show how simple JSON really is. There isn't much to JSON, unlike XML where all manner of meta-information can exist in attributes and such. Also, unlike XML, JSON sticks to Arrays and Hashes for its document structure, whereas XML is much more free-form. While this may sound like a disadvantage at first, it quickly becomes apparent that JSON covers just about every use case for XML while keeping things simple.

  1. About.com
  2. Technology
  3. Ruby
  4. Tutorials
  5. Using JSON: Structure of a JSON Document

©2014 About.com. All rights reserved.