125 The History of XML — Connecting Information Across the Web

The Technologies That Built the Web

Throughout the history of computing, one of the greatest challenges has been finding reliable ways for different computer systems to exchange information. A program running on one computer might store information differently from a program running on another. Even when both systems contained the same information, transferring it between them could be difficult.

XML, or Extensible Markup Language, emerged as an important solution to this problem. It provided a standardized way to organize, describe, store, and exchange structured information.

Although XML is not as visible to everyday web developers as HTML, CSS, JavaScript, or PHP, it has played an enormous role in the development of the internet. It helped connect websites, business applications, publishing systems, document formats, and web services.

And perhaps most surprisingly, XML remains widely used today.

Before XML: The Problem of Incompatible Information

In the early days of computing, software applications frequently used their own proprietary file formats. Information created in one program could be difficult or impossible to use in another without specialized conversion software.

As computer networks expanded, this problem became increasingly important. Businesses, universities, government agencies, and research organizations needed dependable methods of sharing information across different computers and operating systems.

One early solution was SGML, or Standard Generalized Markup Language, which became an international standard in 1986.

SGML provided a system for defining the structure of documents. Instead of describing only how information should appear on a screen or printed page, it could identify the meaning and organization of that information.

For example, a document might identify its title, author, chapters, sections, and references independently of how those elements were displayed.

SGML was powerful, but it was also complex. Implementing it required considerable effort, and its flexibility made it difficult to use in simpler web applications.

As the World Wide Web expanded during the 1990s, developers began looking for a simpler approach.

1998: XML Becomes a Web Standard

XML was developed through the World Wide Web Consortium, commonly known as the W3C. Its first official recommendation was published on February 10, 1998.

The goal was to preserve many of SGML's strengths while creating a simpler language suitable for internet applications.

XML was designed to be:

• Readable by humans and computers.
• Independent of operating systems and programming languages.
• Capable of representing complex structured information.
• Extensible, allowing developers to define their own elements.
• Strict enough to be processed consistently by software.

Unlike HTML, which provides a standardized vocabulary for web documents, XML does not prescribe one universal set of element names. Developers can create element names appropriate to their information.

This flexibility became one of XML's greatest strengths.

How XML Works

XML organizes information using elements enclosed in angle brackets. The structure resembles HTML, but the purpose is different.

Consider a simple record describing a website:

    Zehr.net
    Web Development
    true

The opening and closing tags identify individual pieces of information. The outer website element contains the entire record, while the inner elements describe specific properties.

A program reading this XML can identify the website's name, category, and status without needing to understand how the information should be displayed.

XML also supports attributes:

    Zehr.net

Here, the id and status attributes provide additional information about the website element.

XML has strict syntax rules. Elements must be properly nested, opening tags must have matching closing tags unless they are self-closing, and the document must have a single root element.

These rules make XML less forgiving than HTML, but they also help software process information predictably.

XML and HTML: Similar Appearance, Different Purposes

XML and HTML share a common ancestry in SGML, and their syntax can look remarkably similar.

However, their primary purposes are different.

HTML describes the structure and meaning of web page content. A browser understands standard HTML elements such as headings, paragraphs, images, and links.

XML describes structured information using a vocabulary defined by the application or document format.

For example, an HTML heading tells a browser that text is a heading. An XML element named product might identify a product record, but a browser does not automatically know how that product should be displayed.

XML separates the structure of information from its presentation. Applications can then interpret, transform, or display that information as needed.

The Rise of XML in the Early 2000s

During the late 1990s and early 2000s, XML gained tremendous popularity.

Businesses needed ways to connect databases, inventory systems, accounting software, publishing systems, and applications developed by different vendors.

XML offered a common format for exchanging information between these systems.

Instead of requiring two applications to use the same database or programming language, each could exchange structured XML documents.

XML became particularly important in enterprise computing, where large organizations often operated many independent systems.

It also supported a growing family of related technologies, including XML Schema, XPath, XSLT, and XML namespaces.

These technologies made it possible to validate XML documents, locate specific information, transform documents into other formats, and combine vocabularies without naming conflicts.

XML and Web Services

As websites evolved from collections of documents into interactive applications, developers needed ways for servers to communicate with one another.

XML became a major component of early web services.

SOAP, originally known as Simple Object Access Protocol, used XML messages to exchange information between applications.

A business application might send an XML request asking another system for inventory information. The receiving system would process the request and return an XML response.

SOAP-based services became common in financial systems, government applications, healthcare systems, and large business networks.

Although many newer web APIs favor JSON, SOAP and XML remain important in established enterprise systems.

XML and MySQL: Different Tools for Different Jobs

One common source of confusion is the relationship between XML and database systems such as MySQL.

Both can contain structured information, but they were designed for different purposes.

MySQL is a relational database management system. It stores information in tables and provides powerful methods for searching, updating, organizing, and relating records.

XML is a structured document and data exchange format. It describes information in a form that other software can interpret.

For example, a website might store hundreds of articles in a MySQL database. PHP could retrieve selected articles and generate an XML document for another application.

The XML document would not replace the database. It would provide a way to share information from that database.

In some applications, XML files can serve as a form of data storage, particularly for configuration settings, documents, or relatively small collections of information.

However, XML alone does not provide the indexing, transaction processing, query optimization, and other database capabilities associated with MySQL.

These technologies often complement one another rather than compete.

RSS: XML Delivers News and Podcasts

One of XML's most recognizable applications is RSS, a family of formats used to distribute frequently updated information.

RSS feeds allow websites to publish structured lists of articles, news items, and other content that software can retrieve automatically.

Podcasting became an especially important use of RSS.

A podcast feed can describe the podcast itself and provide information about individual episodes, including titles, descriptions, publication dates, and audio file locations.

Consider this simplified RSS example:

    
    Technology and the Web
    https://zehr.net/

    
        
        Exploring XML
        
    

In a production podcast feed, additional information is typically included, such as unique episode identifiers, publication dates, and podcast-specific metadata.

Podcast applications periodically retrieve these XML feeds to discover new episodes and obtain information about the available audio.

This means that a website can store podcast information in MySQL, generate an RSS feed using PHP, and distribute episodes to podcast applications through XML.

It is a practical example of several web technologies working together.

XML Sitemaps and Search Engines

Another important application of XML is the website sitemap.

An XML sitemap provides search engines with a structured list of URLs that a website owner wants them to know about.

For example:

    
        https://zehr.net/
    

A sitemap can help search engines discover pages, especially on larger websites or websites with complex navigation.

However, inclusion in a sitemap does not guarantee that a page will be indexed or appear in search results.

XML sitemaps remain an important part of technical search engine optimization.

XML Inside Modern Documents

Many people use XML every day without realizing it.

Modern Microsoft Word documents with the .docx extension and Excel spreadsheets with the .xlsx extension use file formats based on XML.

These files are generally ZIP packages containing XML documents and other resources.

The XML describes elements such as paragraphs, formatting, tables, spreadsheet cells, and document relationships.

This approach helps software organize complex documents and provides standardized formats that other applications can interpret.

XML is also used in SVG, or Scalable Vector Graphics. An SVG image describes shapes, paths, text, and other graphical elements using XML syntax.

Unlike traditional raster images, SVG graphics can scale to different sizes without losing the sharpness of their vector shapes.

Thus, XML plays a role in both office documents and modern website graphics.

JSON Changes the Direction of Web Development

As JavaScript became increasingly important in web applications, another data format gained popularity: JSON, or JavaScript Object Notation.

JSON provided a relatively compact and convenient way to represent structured data.

For example:

{
    "name": "Zehr.net",
    "category": "Web Development",
    "active": true
}

JSON is often easier to work with in JavaScript applications, and it became the preferred format for many modern web APIs.

Compared with XML, JSON generally requires less markup for simple data structures and maps naturally to common programming language data types.

XML, however, offers capabilities that remain valuable in document-oriented systems, including mixed text and markup, namespaces, sophisticated schema validation, and document transformation technologies.

The emergence of JSON did not make XML obsolete. Instead, the two formats found different strengths and areas of application.

Why XML Remains Important

Technology often evolves without completely replacing what came before.

XML is an excellent example.

Although it is no longer the default choice for many new web APIs, XML continues to support important technologies and established information systems.

Its use in RSS, podcast feeds, XML sitemaps, SVG, office documents, enterprise applications, and industry-specific data standards gives it an enduring role in computing.

XML also helped establish an important principle: information should be represented in standardized, structured formats that different computer systems can understand.

That principle remains central to modern software development, whether information is exchanged through XML, JSON, or other formats.

Looking Back at XML's Contribution

XML did not create the internet, nor did it replace databases or programming languages. Instead, it helped solve a fundamental problem: how to exchange structured information between different systems reliably.

Its influence extended into web publishing, business applications, document formats, graphics, and the development of web services.

For website developers, XML demonstrates how different technologies can work together. A database stores information, PHP processes it, XML organizes it for exchange, and another application interprets the results.

More than a quarter-century after becoming a web standard, XML continues performing useful work behind the scenes.

And that may be its greatest achievement. A technology does not need to be visible to remain essential.

XML helped teach the web how to exchange information, and the systems built around it continue to connect our digital world.