XML

link: Web Data Handling and Formats

XML (eXtensible Markup Language)

Overview

XML is a flexible, structured markup language used in web development and for storing and transporting data. Developed in the late 1990s, it was designed to be both human-readable and machine-readable. XML is a W3C-recommended standard and is a fundamental technology in a wide range of data applications.

Key Features of XML

Key Features of XML

• Self-descriptive: XML allows the definition of custom tags and the creation of all kinds of data structures, such as lists, trees, and records. This makes it both versatile and adaptable to many different types of applications.
• Platform-agnostic: Being text-based, XML files are platform-independent. They can be used across different operating systems and environments without compatibility issues.
• Extensible: Users can create their own custom tags according to the needs of their application. There are no predefined tags as in HTML, giving XML the flexibility to serve in diverse applications.
• Strong Support for Unicode: XML inherently supports Unicode, allowing almost any character from any human language to be used, which is crucial for internationalized applications.

How XML Works

How XML Works

1. Structure: An XML document is structured as a tree of elements, each with tags and content. An element starts with a start-tag and ends with an end-tag, with content in between.
2. Syntax Rules: XML has strict syntax rules. It must begin with a declaration that defines the XML version and character encoding used in the document.
3. Tags and Elements: Tags in XML are user-defined and provide a way to label the data, which can then be easily interpreted by software.
4. Attributes: Elements can have attributes, which provide additional information about elements. Attributes are always located in the start-tag of an element.
5. Parsing: XML data needs to be parsed with an XML parser. This parser converts data into a structure that can be easily read by the application logic.

XML Syntax

XML Syntax

Basic XML Document

Here’s an example of a basic XML document that includes a declaration, elements, attributes, and nested elements:

<?xml version="1.0" encoding="UTF-8"?>
<bookstore>
    <book id="b1">
        <title>Understanding XML</title>
        <author>John Doe</author>
        <price currency="USD">29.99</price>
    </book>
    <book id="b2">
        <title>Advanced XML Features</title>
        <author>Jane Smith</author>
        <price currency="USD">35.99</price>
    </book>
</bookstore>

Attributes vs. Elements

Attributes provide additional information about elements. Comparing storage as attributes or elements affects accessibility and readability:

<!-- Using attributes -->
<employee id="E123" department="Finance"/>
 
<!-- Using elements -->
<employee>
   <id>E123</id>
   <department>Finance</department>
</employee>
 

Attributes are typically used for metadata, while elements handle data that could benefit from more structure.

Nested Elements

<university>
   <department name="Engineering">
       <faculty>Technology</faculty>
       <students>
           <student id="S1001">Alice</student>
           <student id="S1002">Bob</student>
       </students>
   </department>
</university>
 

XML allows for complex data structures through nested elements, ideal for hierarchical data such as academic records or organizational charts:

Special Characters and CDATA

CDATA sections are used to include special characters or unescaped data within XML documents:

<description>
   <![CDATA[
       This is a description text that can contain unescaped characters like <, >, or & without causing errors.
   ]]>
</description>
 

CDATA sections ensure that the data inside is treated purely as text, not XML markup.

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JSON vs XML

Comparison

Feature	JSON	XML
Verbosity	Lightweight and less verbose	More verbose, leading to potentially larger files
Readability	High readability and ease of use	Readable but can be cumbersome due to verbosity
Complexity	Lower complexity, easier to parse	Higher complexity, robust parsing required
Data Structures	Ideal for array and key-value pairs	Better for complex hierarchical data structures
Metadata Support	Limited metadata capabilities	Extensive metadata support through attributes
Scalability	Highly scalable for web and mobile applications	Scalable but better suited for enterprise systems
Security	Basic security suitable for web data	Advanced security features like support for XML Signature
Interoperability	High with web technologies	High across various software and systems
Use Cases	APIs, web configurations, client-server apps	Complex document-based applications, enterprise data exchange
Encoding Support	Unicode support directly	Extensive support for various encodings

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References

What Is XML? | Postman Blog