What is XML: Overview on Comments, Attributes, Tags, Syntax and more

I'm sure you all know that HTML plays a vital role in app development. It is a markup language that defines how the information is displayed on the screen. But have you ever wondered what carries and stores the data? And perhaps governs the structure of data being presented? You guessed it right. This is done by XML. This article on what is XML will help you understand this markup language in detail.  

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What Is XML?

XML, short for eXtensible Markup Language, is a set of tags and codes that help carry the data presented on the website. XML does not define how the data is displayed; instead just transports it. The main objective of XML design is to ensure simplicity and compatibility, making it platform and programming language independent. 

You will now look at the features of XML after you have learned what is XML.

Features of XML

XML comes with a lot of features that make it stand out from other languages. Here is the list of come salient features of XML 

• Extensible and Human Readable  - Most XML applications will work as expected even if new data is added. 
• Overall Simplicity - XML simplifies data sharing, data transport, platform changes, and data availability. XML makes it easier to extend or upgrade to new operating systems, new apps, or new browsers without losing data. Data can be made available to a variety of "reading machines," such as people, computers, voice machines, news feeds, and so on.
• Separates data from HTML - Data can be saved in different XML files using XML. This way, you can concentrate on using HTML/CSS for display and layout while knowing that changes to the underlying data will not require HTML changes.
• Allows XML Validation - A DTD or XML schema can be used to validate an XML document. This ensures that the XML document is syntactically valid and prevents any problems from arising from a faulty XML.
• XML supports Unicode - XML is Unicode-compatible, which means it can communicate practically any information in any written human language.
• Used to create new languages - XML has spawned a slew of new Internet languages.
• For describing available web services,  WSDL can be used
• As markup languages for portable devices, WAP and WML are used
• For news feeds, RSS languages are used
• RDF and OWL are used to describe resources and ontologies
• SMIL is a standard for specifying web-based multimedia

Now that you are familiar with what is XML and the features or the advantages of XML, the following section explains the semantics of an XML document. 

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XML Syntax

Let us now look at the XML syntax and declaration.

The following is the basic XML syntax - 

<?xml version = "1.0" encoding = "UTF-8" ?

<root>

    <child>

        <subchild>.....</subchild>

    </child>

</root>

XML Declaration 

The following code shows the syntax for XML declaration 

<?xml version="version_number," encoding="character_encoding" standalone="yes_or_no" ?>

XML Comments 

Comments are optional. Adding comments to a document can help you comprehend it better. 

<?xml version="1.0" encoding="utf-8"?> <!-- This is XML Declaration-->

XML Tags and Elements 

Except for declarations, tags work in pairs. An opening tag and a closing tag make up each tag pair 

<> is used to enclose tag names. The start and end tags for a tag pair must be identical, except that the end tag must have / after the <.

<employee>

        <firstname>John</firstname>

        <lastname>Doe</lastname>

        <title>Engineer</title>

        <division>Materials</division>

</employee>

In the above example, employee, firstname, lastname, title and division are tags. Tag names are also referred to as elements.

XML Attributes 

In the start tag, the attribute for an element is inserted after the tag name. For a single element, you can add many attributes with distinct names. 

There are two main rules to define an attribute - 

• Attribute values must be within quotes.
• An element cannot contain several attributes with the same name.

Consider the same example as above 

<employee id="be129">

        <firstname>John</firstname>

        <lastname>Doe</lastname>

        <title>Engineer</title>

        <division>Materials</division>

</employee>

Here the “id” is an attribute specific to that employee. 

Now that you are familiar with what is XML and advantages of XML, let’s look at the limitations of XML. 

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Limitations of XML 

• The access speed of XML is not optimized. XML documents are intended to be fully loaded before being used as a data source. Every time the parser reads in the markup, it must do a syntax check. Modern databases, on the other hand, are designed for rapid data lookups and updates.
• XML is not a compact language. There is no standard XML compression technique. Uncompressed text is expected by XML parsers. Either deal with big text files or build a sophisticated method for compressing and decompressing on the fly, which will increase your processing overhead.
• Embedded markup isn't appropriate for all types of data. For text data with a hierarchical structure, XML is the best option. It doesn't provide much in the way of binary data.

Now that you know the major limitations of XML, let’s look at the difference between HTML and XML 

HTML vs XML

Although HTML and XML are markup languages, they have significant differences. Here’s a list of the differences. 

These were some of the major differences between HTML and XML. 

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Next Steps

We hope you found this article 'What is XML?' helpful. Pursuing a credible certification program will be beneficial if you want to gain advanced practical knowledge of full-stack technologies and possibly make it into a profession.

The  Full Stack Java Developer Masters Program from Simplilearn will teach you all you need to know about full-stack programming. This full-stack Java development course is designed to provide a thorough understanding of front-end, middleware, and back-end Java web developer technologies. This program will teach you how to construct an application from start to finish, test and deploy code, store data in MongoDB, and much more.

If you have any  questions or need clarification on this subject, please let us know in the comments section . We’ll help them resolve as soon as possible.