XML, which stands for Extensible Markup Language, is a text-based markup language derived from SGML (Standard Generalized Markup Language). XML’s primary purpose is to facilitate the sharing of data across different systems, particularly systems connected via the internet.

Here are some key features and aspects of XML:

  1. Structure and Syntax:
    • XML provides a structured format for data, with a set of rules for encoding documents in a format that is both human-readable and machine-readable. It uses tags, elements, and attributes, similar to HTML, to structure data.
  2. Self-descriptive:
    • XML documents are self-descriptive; the data structure and types are part of the document itself. This makes XML documents easy to understand and process.
  3. Platform Independent:
    • Being a text-based format, XML is platform independent. This allows for the easy sharing of data between different system architectures.
  4. Extensible:
    • XML is extensible, meaning that it supports a user-defined tag structure allowing for the creation of customized markup languages.
  5. Validation:
    • XML supports the ability to define a schema (using technologies like DTD or XML Schema) which can be used to validate the structure and content of XML documents ensuring they adhere to predefined rules and structures.
  6. Transformation and Presentation:
    • XML documents can be transformed and presented in various ways using technologies like XSLT (Extensible Stylesheet Language Transformations) and CSS (Cascading Style Sheets).
  7. Data Exchange:
    • XML is widely used for data exchange, configuration files, and in web services like SOAP (Simple Object Access Protocol). It allows for structured data exchange between many different types of applications.
  8. Internationalization:
    • XML supports internationalization and localization as it can handle different human languages and encoding schemes.
  9. Parsing:
    • XML data needs to be parsed by an XML parser to be used in other applications. There are many XML parsers available in different programming languages.
  10. Verbosity:
    • One common criticism of XML is its verbosity, which results in larger file sizes compared to other data formats like JSON or Protobuf, potentially leading to slower data transmission and parsing.
  11. Legacy Systems:
    • Although newer technologies like JSON have become more popular in many use cases, XML is still widely used, especially in legacy systems and certain domains like healthcare (HL7), finance, and telecommunications.

XML has played a pivotal role in the evolution of data interchange and has been foundational in the development of many modern web technologies and standards.