XML, YAML, JSON; Differences and Similarities

Data is moved around a lot in today’s digital space; sensors, IoT devices, social media platforms, user interactions on websites and applications, transactions in financial systems, and more. Governments, corporations, businesses, and individuals all make decisions based on available data. Data serialization helps different computer systems understand each other by translating information into a common language. It's like translating a message so that everyone can communicate effectively, making things run smoothly in the digital world. This is essential for developers to build efficient, and interoperable software applications that can effectively exchange, store, and process data in various contexts.

In this article, we will explore the 3 popular text-based data serialization formats, i.e. XML, YAML, and JSON, and their similarities and differences. You should be able to choose the right data format for your next project. This article requires that you have a basic understanding of HTML and data structures i.e. primitive data types.

XML (eXtensive Markup Language)

XML is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. It is defined by the W3C's XML 1.0 Specification and by several other related specifications, all of which are free open standards.

It is a markup language, meaning that it uses tags to identify and structure data, making it easy to understand and parse. It is a simple, flexible, and adaptable language that is used for data exchange, storage, and transmitting data across different applications. Additionally, XML is self-descriptive, platform-independent, vendor-independent, and extensible, and requires documents to be well-formed and valid according to specific rules and guidelines.

In programming, XML can be used to create configuration files, internet messaging, object persistence, data auditing, and visualization.

An XML tree structure is a hierarchical representation of an XML document, where each element is a node in the tree. This structure consists of the root node, the topmost element that represents the entire document. We can have the parent node, which is the element that contains other elements, the child node, an element that is contained in another element, and the sibling node which are elements that have the same parent node.

Here is the basic structure of an XML document;

<parent>
  |-- <child1>
  |    |-- <grandchild1>
  |    |-- <grandchild2>
  |-- <child2>
  |    |-- <grandchild3>
  |-- <child3>

XML syntax is much like HTML; it contains one or more elements that have both the start tags and end tags. Each element has a type, identified by name, and may have a set of attributes that has a name and a value. Every start tag must have a corresponding end tag. Empty elements must not include white spaces between the tags. Elements have a type that is determined by the name value. XML tags and structure are not predefined, unlike HTML. The author must define the structure and tags.

Let’s consider the example below;

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <database>
    <username>admin</username>
    <password>password</password>
    <host>localhost</host>
  </database>
  <server>
    <port>8080</port>
    <timeout>300</timeout>
  </server>
</configuration>

In this example, the XML file defines configuration settings for a database and a server. At the top of the document is the XML declaration which specifies the version of XML being used.
XML is used for exchanging data across different platforms. In some cases, it is used as a configuration file as it provides a human-readable and easy-to-parse format for storing settings and preferences. Other areas in document management such as storing and retrieving data, web services with SOAP (Simple Object Access Protocol) and REST (Representational State of Resource) web services, localization and internationalization for translating text and formatting data for different languages and regions, etc.

YAML (YAML Ain't Markup Language)

YAML, which rhymes with “Camel”, is a human-friendly, data serialization language designed to work well in modern programming languages. YAML is a user-friendly choice for data handling and processing because it uses few structural characters to provide information.

YAML supports primitive data types such as strings, numbers, boolean, maps, and arrays, allowing for the representation of diverse data structures. Programming languages that are built around these primitive data structures work well with YAML including Javascript, Perl, Python, PHP, and Ruby.
The syntax and structure of YAML documents are designed to be human-readable and intuitive, portable between programming languages, match the native data structures of dynamic languages, have a consistent model to support generic tools, support one-pass processing, (i.e. to parsed document sequentially from start to finish without needing to revisit previously parsed parts), be expressive and extensible, and lastly be easy to implement and use. It relies on consistent indentation using spaces (not tabs) to indicate nesting levels within the document.

For example;

fruits:
  - apple
  - banana
  - orange

In this snippet, the list of fruits is indented with two spaces under the key "fruits," indicating that it is a child element of the "fruits" key. Each item in the list is further indented under the list indicator "-" with two additional spaces, showing their association with the list.
The indentation determines the hierarchy and relationships between data elements, such as key-value pairs and lists;

# Configuration settings for a web server
server:
  # Server settings
  port: 8080        # Port number for the webserver
  host: localhost   # Hostname for the webserver
  ssl_enabled: true # Whether SSL is enabled

database:
  # Database connection settings
  type: mysql            # Type of database (e.g., MySQL, PostgreSQL)
  host: db.example.com   # Hostname for the database server
  port: 3306             # Port number for the database connection
  username: admin        # Username for database authentication
  password: secure_password # Password for database authentication
  database_name: web_db  # Name of the database to connect to

The example above shows how YAML's indentation-based hierarchy is used to represent the relationships between different configuration settings in a clear and structured manner. The ‘#’ provides explanations and context for each section and key-value pair.

YAML's benefits include readability and expressiveness, but it also poses challenges. Its whitespace rules and flexibility can cause confusion and mistakes, and there are security risks with poorly crafted YAML data. YAML’s lack of standardization and learning curve, along with possible performance issues and schema validation complexities, require careful handling by developers using YAML in various applications.

JSON (JavaScript Object Notation)

JSON (JavaScript Object Notation) is a lightweight data interchange format. It is known for its simplicity and minimalism. It uses a lightweight, text-based format to represent data structures consisting of key-value pairs and arrays, making it highly efficient for transmitting and parsing data over the internet. It stands tall as one of the most favored methods for structuring data, offering simplicity, flexibility, and compatibility across various platforms and programming languages.
It is a lightweight data-interchange format that is easy for humans to read and write and straightforward for machines to parse and generate. Its syntax is derived from JavaScript object notation, but JSON is language-independent, making it versatile for use across different programming languages.
JSON data is organized into key-value pairs, where each key is a string and each value can be either an object enclosed in curly braces {} made up of key-value pairs separated by colons: arrays enclosed in square brackets [] containing comma-separated values, strings enclosed in double quotes, numbers representing numeric values, booleans representing true or false values, and null representing an empty value.

{
  "name": "John Doe",
  "age": 30,
  "isStudent": false,
  "address": {
    "street": "123 Main St",
    "city": "Anytown",
    "country": "USA"
  },
  "languages": ["JavaScript", "Python", "Java"]
}

The above example represents information about a person named John Doe (string), aged 30 (numeric), not currently a student(boolean value), address (object), and language (array).

JSON's versatility and simplicity make it suitable for a wide range of use cases across various industries and domains. It is a lightweight and easy-to-read data interchange format. It is widely used for data exchange between web servers, web applications, and mobile apps. Its simplicity and flexibility make it a popular choice for many applications and services. JSON is also used for data storage and serialization and is supported by many programming languages. Its versatility and ease of use have made it a standard format for data exchange and storage.

Though JSON is very popular, it has its downside. Lack of comments which makes it challenging for developers to add explanatory notes, explicit support of data types resulting in issues with data validation, limited error handling leading to potential runtime errors or data corruption, and schema evolution making it difficult to manage data structures over time are areas that could be addressed to solidify JSON’s position as a versatile reliable data-interchange format.

Choosing the Right Format

The table below summarizes the use cases for XML, YAML, and JSON.

The table above focuses only on the use cases, making it easier to compare the suitability of XML, YAML, and JSON for each scenario.

Conclusion

In conclusion, the evolution of data serialization continues to be driven by the need for simplicity, readability, flexibility, and performance. While JSON and YAML have gained significant adoption, there is ongoing innovation and exploration of new serialization formats to meet the evolving needs of modern software development.