XML Fundamentals

XML (eXtensible Markup Language) is a text-based format used to store and transport structured data. Unlike HTML, which focuses on displaying information, XML is designed to describe and organize data in a readable and flexible way. It allows developers to define their own tags, making it suitable for many different types of applications and data exchange systems.

An XML document must follow strict structural rules. It must contain a single root element that encloses all other elements. Elements must be properly nested and every opening tag must have a matching closing tag. This strict structure ensures that XML documents can be reliably processed by software systems.

XML documents are composed of elements and attributes. Elements represent the main structure of the data, while attributes provide additional information about those elements. Attributes appear inside the opening tag and usually describe properties or metadata related to the element.

XML naturally represents hierarchical data structures by nesting elements inside one another. Parent elements contain child elements, forming a tree-like structure that is easy for both humans and machines to understand.

XML can represent collections of similar items by repeating the same element within a parent container. This approach is commonly used for lists such as records, products, or messages.

XML elements can contain text content that represents data values. Because XML uses certain characters as part of its syntax, special characters such as <, >, and & must be written using escape sequences.

A well-formed XML document follows the basic syntax rules of XML. These include having a single root element, properly nested tags, and correctly written attributes. Well-formed documents can be parsed and processed by XML tools and applications.

XML documents can be validated against a schema or definition that specifies the allowed structure and data types. This ensures that the document follows a predefined format and contains the expected elements and values.

XML is widely used for exchanging structured data between different systems and applications. Because it is text-based and platform-independent, it allows data to be shared reliably across networks and between software written in different programming languages.