- What is XML?
- Basic Features of XML Files
- What is the Structure of an XML File?
- What is XML Used For?
- When and Where is XML Used?
- Basic Terms Related to XML
- Technical Advantages of XML
- Disadvantages of XML
- XML vs JSON
- Real-Life Examples of XML
- Most Frequently Asked Questions About XML
- Conclusion
As technology continues to evolve, the storage, sharing, and organization of data have become increasingly important. At this point, XML (Extensible Markup Language) files play a crucial role in carrying and storing structured data. So, what is an XML file, what is it used for, and why is it used so widely? Here are the details you need to know about XML files.
What is XML?
XML is the abbreviation for "Extensible Markup Language." It means "Genişletilebilir İşaretleme Dili" in Turkish. It was developed by W3C (World Wide Web Consortium) and standardized in 1998.
It is a markup language like HTML, but the fundamental difference is that it is used to carry and define data. While HTML focuses on displaying data, XML focuses on describing what the data is.
Basic Features of XML Files
• Contains user-defined tags (e.g.,
• Has a hierarchical (tree structure) data structure.
• Is platform and software independent.
• Supports Unicode character sets like UTF-8 or UTF-16.
• Has a commenting feature ().
• Enables the structuring of data.
What is the Structure of an XML File?
XML files consist of opening and closing tags. Here is a simple example:
<?xml version="1.0" encoding="UTF-8"?>
In this example:
•
• Sub tags:
• Each tag has a closing tag ().
• The data is readable and meaningful.
What is XML Used For?
1. For Data Transport
XML is ideal for performing data exchange between systems in a standard structure. For example, an e-commerce site can send product information to another system in XML format.

2. In Web Services
SOAP-based web services are based on XML format. Data exchange in APIs can be achieved using XML.
3. Configuration Files
Configuration settings in platforms such as Java, .NET, and Android are done using XML (example: web.config, AndroidManifest.xml).
4. For Data Storage
XML can be used instead of a database, especially for small datasets.
5. Office Applications
Microsoft Office (especially Word and Excel) uses XML-based file formats (.docx, .xlsx, etc.).
6. In Sectoral Documents
Many structural data such as invoices, customer information, order records, and product catalogs can be stored using XML.
When and Where is XML Used?
XML is used not only for transporting data but also for structuring that data. Developers prefer XML in both web services and local applications. It is especially common in the following areas:
• Information transfer between software systems
• Mobile application configurations
• Data exchange in web applications
• Banking and e-invoice systems
Additionally, XML files can also be converted to HTML using technologies like XSLT for data presentation to end users. However, it is not as visualization-focused as HTML.
Basic Terms Related to XML
• DTD (Document Type Definition): The schema that defines the structure of an XML file.
• XSD (XML Schema Definition): Defines the data types and structure of XML content.
• XPath: Used to query specific pieces of data in XML documents.
• XSLT: Used to convert XML data into different formats (e.g., HTML).
• XML Parser: The software component that reads and parses the XML file.
Technical Advantages of XML
• Platform Independence: XML works everywhere regardless of operating system or software.
• Wide Compatibility: Almost all programming languages support XML.
• Unicode Support: Can handle characters in all languages smoothly.
• Ability to Add Comments: It is possible to leave descriptive notes within the code.
• Extensibility: Users can create custom tags according to their needs.
Disadvantages of XML
• File Size: Due to the abundance of tags, it can be larger compared to alternatives like JSON.
• Efficiency: XML parsing is relatively slower.
• Lack of Visual Presentation: Does not produce visual output directly; it needs to be transformed.
XML vs JSON
| Feature | XML | JSON |
|---|---|---|
| Data Structure | Hierarchical (tree structure) | Object/array-based |
| Readability | Can be relatively complex | Simpler |
| File Size | Larger | Smaller |
| Schema Support | DTD, XSD | JSON Schema |
| Adding Comments | Yes | No |
Real-Life Examples of XML
• RSS Feeds: Content updates on blog/news sites are done using XML.
• e-Invoice Systems: In Turkey, the e-document formats of the Revenue Administration are XML-based.
• Banking and Finance: Money transfers and reporting can be done via XML.
• Mobile Applications: Interfaces and configurations in Android applications are defined using XML.
Most Frequently Asked Questions About XML
Why are XML files used so widely?
The main reasons for the widespread use of XML are:
• Operating independently of the platform
• Readable by both humans and machines
• Extensible and customizable tag structure
• Being a universal standard for carrying and defining data
What is the difference between XML and HTML?
While HTML describes how data should look (presentation-focused), XML defines what the data is (meaning-focused). In HTML, tags are fixed, while in XML they are user-defined. In short, HTML shows, XML explains.
Why has JSON started to be used instead of XML?
JSON is a data format that takes up less space and works more naturally with JavaScript. Therefore, it offers a faster and more practical solution, especially in web-based applications. However, XML is still used in many systems because it is more suitable for complex data structures and has a stronger schema definition (XSD).
Is XML secure?
XML itself is neither secure nor insecure; however, security vulnerabilities can arise in XML-based systems. Therefore, XML data obtained from external sources should always be validated and filtered before processing. Additionally, precautions should be taken against XML External Entity (XXE) attacks.
Is learning XML difficult?
No. Learning the basics of XML is quite easy because it has a human-readable structure. After learning the basic tag structure, more advanced topics like DTD, XSD, and XPath can be explored.
Which applications use XML?
XML frequently appears in the following areas:
• Web services (especially SOAP)
• Android applications
• Configuration files
• Microsoft Office documents
• E-government, e-invoice systems
• RSS feeds
• Banking and finance systems
How to open an XML document?
To open an XML file, a text editor such as Notepad, Visual Studio Code, or Sublime Text is sufficient. XML editors or browser extensions can be used for more advanced viewing and validation.
Is XML sufficient on its own?
No. XML only defines and carries data. Other tools (e.g., XSLT, XSD, parsers) are needed to process, visualize, or validate that data.
Can an XML file be used instead of a database?
It can be used in small-scale applications or temporary data storage solutions. However, for large datasets or complex relational structures, XML cannot replace databases. Databases are much stronger in terms of performance, security, and querying capabilities.
Conclusion
XML is a powerful, flexible, and platform-independent format for transporting, defining, and structuring data. Its extensible structure allows it to be used in a wide range of fields. It plays an indispensable role, especially in data transfer and configuration needs between systems.
Although lighter alternatives like JSON are preferred in many web applications, XML still has a wide usage area, from e-government systems to banking, and from mobile applications to ERP software.