The Extensible Markup Language (XML) is a widely used markup language that defines rules for encoding documents in a format that both humans and machines can read. It provides a structured way to represent data, making it easy to exchange information between different systems. XML uses a hierarchical structure to model data, allowing for flexibility and extensibility.
At the core of XML’s data modeling structure are elements, which are enclosed within tags. Elements can have attributes that provide additional information about the data they represent. These attributes are specified within the opening tag of an element.
Elements
An element in XML consists of a start tag, content, and an end tag. The start tag is enclosed within angle brackets (<>) and contains the name of the element. The end tag also uses angle brackets but includes a forward slash (/) before the element name.
For example:
<book>
<title>Harry Potter and the Philosopher's Stone</title>
<author>J.K. Rowling</author>
</book>
In this example, <book> is the start tag for the ‘book’ element, while </book> is its corresponding end tag. The content between these tags represents the data associated with the ‘book’ element.
Attributes
Attributes provide additional information about elements.
They are specified within the opening tag and consist of a name-value pair separated by an equals sign (=). The attribute value should be enclosed within quotation marks (”).
For example:
<book category="fiction">
<title>Harry Potter and the Philosopher's Stone</title>
<author>J. Rowling</author>
</book>
In this example, the attribute category is added to the ‘book’ element with a value of “fiction”. This attribute provides additional information about the book.
Hierarchical Structure
XML allows for the creation of a hierarchical structure by nesting elements within each other. This nesting creates parent-child relationships between elements, forming a tree-like structure.
For example:
<library>
<book category="fiction">
<title>Harry Potter and the Philosopher's Stone</title>
<author>J. Rowling</author>
</book>
<book category="non-fiction">
<title>Sapiens: A Brief History of Humankind</title>
<author>Yuval Noah Harari</author>
</book>
</library>
In this example, the ‘library’ element is the parent element, while ‘book’ elements are its child elements. Each ‘book’ element has its own nested elements representing its properties.
Lists
In XML, lists can be represented using repeating elements or by using a single element with multiple values separated by delimiters.
For example:
<fruits>
<fruit>Apple</fruit>
<fruit>Banana</fruit>
<fruit>Orange</fruit>
</fruits>
In this example, the ‘fruits’ element contains multiple ‘fruit’ elements, each representing a different fruit in the list.
Conclusion
XML provides a powerful and flexible structure for modeling data. By using elements, attributes, and a hierarchical structure, XML allows for the representation of complex data in a clear and organized manner. Understanding the basics of XML’s data modeling structure is essential for working with XML documents and exchanging information between different systems.