What is XML?
What is XML?
Published: 02 Apr 2023 10:32
Extensible Markup Language (XML) is a versatile markup language and file format designed to store, transmit, and reconstruct arbitrary data.
Unlike HTML, which focuses on how data looks, XML focuses on what data is. It provides a flexible set of instructions for encoding documents in a way that is readable by both humans and machines. This makes it a cornerstone for database entries, financial transactions, and cross-platform content creation.
The Building Blocks of XML
A "well-formed" XML document relies on a strict logical structure:
Root Element: The "parent" tag (e.g.,
<library>) that contains all other data in the file.Nested Elements: Child tags (e.g.,
<book>,<author>) that describe specific data points.Self-Terminating Tags: For null or empty data, a forward slash is used to close the tag immediately (e.g.,
<para />).Custom Extensibility: Authors can define their own tags (like
<ISBN>or<Publisher>) to suit their specific needs.
Restricted Characters (Entities)
Certain characters are reserved for XML syntax. To use them within text, you must use predefined entities:
| Symbol | Entity Code | Description |
|---|---|---|
| < | < |
Less than (Open angle bracket) |
| > | > |
Greater than (Close angle bracket) |
| & | & |
Ampersand symbol |
| " | " |
Double quotation mark |
The Advantages
Platform-Neutral: Works on any system or programming language.
Unicode Compatible: Can transport data in any human language.
Separation of Concerns: Data can be updated in XML without changing the GUI presentation.
The Disadvantages
Verbose: Redundant syntax leads to larger file sizes than JSON.
No Array Support: Lacks native support for array structures.
Complex: Can be less readable and more expensive to transmit at scale.
Final Thoughts
While newer formats like JSON have gained popularity for their brevity, XML remains a fundamental pillar of web technology. Its strict validation through DTD and Schemas ensures data integrity, making it indispensable for enterprise-level systems. Understanding XML isn't just for developers—it's for anyone who wants to grasp how modern websites and databases communicate behind the scenes.
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