What is XML?

Updated March 13, 2023

Introduction to XML

XML can be expanded as ‘Extensible Markup Language’, a text-based language used to define markup documents to publish on the web. It can contain data and its formatting details as common data. XML can be used for its significant data storage capacity, holding public standards, and being extensible compared to another Markup language. This language was formed from extracting the properties of SGML, that is, Standard Generalized Markup Language.

Understanding XML

There are several important features of XML that make it very useful in several spheres of technology. They are stated as below:

• Extensible: It allows us to create different tags with proper description or language according to the need.
• Data storage: It is used to store the data irrespective of how it will be presented in the next step.
• Public standard: An organization called World Wide Web Consortium or W3C developed it and made it available as an open standard.

Uses of XML

There are several uses of it, like simplifying the creation of HTML documents, reloading databases and many others.

They are described as below:

1. This can be used to express any type of data, and there are not many restrictions on it.
2. It is used in the backend to simplify the creation of HTML document which is used in big websites.
3. They are easily merged with style sheets which can help to create a lot of different output.
4. They are used for data exchange between different organizations or different systems.
5. They facilitate data handling and are used to store and arrange data in desired ways.
6. They are used for reloading databases or for different maintenance activities.

There are a set of rules defined by XML in line with markup language used for encoding documents to be read both by humans and machine. Hence, the markup language can be defined as any kind of information that produces the proper meaning of the document in certain ways, which identifies how the different parts of the document are related to each other. Moreover, a markup language consists of symbols placed in the document that indicate the different parts of the document.

Below is a sample XML piece with a markup appearance:

<information>
<lines>How are you</lines>
</information>

The above example shows markup symbols which are often called as tags like <information> ….. </information> and <lines> …. </lines>. The tags <information> and </information> demarcates the start and end of the XML code fragment. The tags <lines> and </lines> encapsulates the line “How are you”.

XML should not be confused with a programming language. Programming language consists of specific rules and conventions that can be followed to create programs. And these programs instruct the computer to perform the defined tasks. However, XML does not qualify to be a programming language as it does not perform any computations or algorithms. It is generally stored in text files and processed by the software design for interpreting XML.

How does XML make working so easy?

Writing XML documents are easy as compared to other markup languages. There are no predefined rules to follow, and authors can create their own tags and rules to serve their needs. In this way, XML is very flexible in terms of developing the document. It can also be put in the backend of any web application to maintain the style sheets. These style sheets can be updated by updating the XML documents.

Top Companies

Due to its simple nature, it is being used by all leading companies like Xerox, Microsoft, Google, Facebook, Ford Motors, and many others.

What can you do with XML?

XML is used for the storage and transportation of data and information. It is purely a document-based technology independent of any specialized software or hardware requirement. It is also a self-descriptive language. Being self-descriptive, it contains sender information, receiver information, a heading, and a message body. Information in an XML document can be added anytime, extending the content of the document making XML extensible. It also simplifies several things like data sharing, data transport, platform changes, and data availability. Moreover, it is a W3C recommendation.

Working with XML

It consists of two parts:

1. Mark up.
2. Text or characters of data.

It can also have a declaration, as shown below. Here the XML version and encoding define the character encoding used in the document. A sample declaration is given below:

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

There are few rules for syntax as defined below:

1. The declaration should have “<?xml>” written in lower case. It is case-sensitive and always should be written in the beginning.
2. If a declaration is present in the XML document, it must be present in the beginning.
3. The encoding given in the XML declaration can be overridden by any HTML protocol used there.
4. The XML document consists of elements and tags. The XML elements are enclosed in triangular brackets.

Element syntax

XML element is closed with either a start or with an end element like <element>….</element> or in simple  clause like <element/>.

Nested elements

It allows the nesting of statements, but they should not overlap each other. It means an end tag of an element must have the same name as that of the most recent unmatched start tag.

Root element

A single XML document has only one root element like below.

<root>
<x>...</x>
<y>...</y>
</root>


Case sensitive

The XML element is always case sensitive, which means that the start and end elements have to be in the same case.

An attribute is a single property of an element that uses a name-value pair. There may be multiple attributes for an element. Below is an example:

<a href = "http://www.samplearticle.com/">Sample</a>

In the above, href is the attribute name, while www.samplearticle.com is the attribute value.

There are few syntax rules defined for attributes as defined below:

• The XML attribute name is case-sensitive.
• There must not be multiple values for the same attribute.
• The attribute values appear in quotation marks, whereas attribute names are defined without quotation marks.
• References are used to add up additional information or mark it up in an XML document. They always begin with the “&” symbol and end with “;”.

Below given are two types of references:

Entity reference

In an entity reference, there is a name defined between the start and end delimiters. Any kind of predefined string like text or mark-up can be used as a name.

Character reference

The character references have references containing a hash mark (“#”) followed by a number. The number refers to the Unicode of a character.

The names of attributes and elements are case sensitive, meaning the start and end attributes should be in the same case. All the character encoding problems can be avoided by saving the document in Unicode UTF-8 or UTF-16 format. This causes all the blanks, tabs, line breaks between the attributes and elements to be ignored. There is some XML reserved syntax that cannot be used directly. There are some replacement entities that are used to avoid this scenario.

Advantages

Below are the advantages of XML:

1. The document standard is an international standard and is maintained by W3C, the organization that is responsible for maintaining web standards. XML documents are not particular to any vendor nor tied to any single application or organization. There are a lot of varieties of document writers that are available in the market. Some of them are often proprietary and work with the software allocated for that particular type of document. However, XML documents can be created in any editor and can be edited on a different editor, thus making them independent of a particular assigned editor. Even Notepad text editor can be used to create XML documents, although it is not recommended.

2. XML tags or XML elements are used to define the structure of an XML document. Once document structure is defined that, processes can be selected like style sheets to manipulate the content and reuse them after manipulation. With content being separated from the display, we can use single-source content in many different contexts. Unlike HTML, it does not have a fixed number of tags or elements, thus allowing the designer to design a document with meaningful tags. It allows designers to create markup language according to their needs. Even new elements can be defined as per requirement giving the designer the ability to make custom elements is a unique feature offered by XML.

3. They provide a feature of reuse of the contents, thereby allowing the different organizations to save much money and effort along with making the authors more efficient. Once the content is created, that can be used in several other documents. XML documents are often manipulated to adjust the needs of different users. Different style sheets can be applied to an XML document to manipulate the content which is appropriate for some particular users or to output different types of documents.

4. The separation of content and format is allowed by XML. A separate style sheet is maintained where the formatting of the XML document is done. Thus, because of this independence, easy updating and maintenance of the document are possible when needed. Also, it is easy for maintaining a consistent stylesheet for all documents when the content is separated from the formatting.

5. It is very useful when publishing a document in more than one language or multiple languages originating from the same source. The override of translations also can be reduced if the content is stored in XML source files. Thus, when publishing the documents in several languages can be done with just a single click. The formatting is automatically applied when publishing the source XML files.

Why should we use XML?

There are many purposes of using XML, like transporting the data in a structured format from a source point to any destination and many others. The tags used in XML are for ensuring the structure of the data. The combination of tags and texts is used to store information. The text is surrounded by tags that are written following pre-defined rules and contains meaningful information about the enclosed text. Thus, it is very easy to store information and transport them very easily.

Why do we need XML?

The need for it is vast as it is used for outsourcing the data primarily. HTML documents use XML to store the data as a backend. It stores the data in a plain text format, and it is independent of the platform, which can be imported or exported or simply move from one place to another without any problem.

Who is the Right Audience for learning XML Technologies?

Though it is pretty easy to learn, a pre-requisite knowledge of XSLT, XQuery and XPath will be good to have for an audience wanting to learn. Apart from these, knowledge of HTML is also a good thing to have.

How will this technology help you in Career Growth?

It is such a technology used almost in all companies using basic data and web operations. The opportunity of having a good salary is also evident from the uses and advantages offered by it.

Conclusion

It is a standard representation of web information that is supported by lots of generic tools, and also it is a notation for hierarchically structured text. It is the encoding for upper-level languages such as RDF for defining information about documents and for OWL to define ontologies. It is also a fundamental building block of the Semantic Web initiative.

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