XML Interview Questions

XML Interview Questions

XML stands for Extensible Markup Language. It provides a document which is pre-defined by a set of rules readable by both human and machine. The main vision of XML is generality, simplicity, and usability. The document is the main focus of the XML, but it can also deal with the arbitrary data structure. Accessing information is a method provided by XML, making it easier for devices to use, display, transmit and store data effectively. There are many tokens or functions provided by XML which are easier to use and provide a base for the usage along with quick documentation.

Some Interview Questions

Give yourself a rating on this software.

This question is to test your confidence and how much you know about the subject in your opinion. This can also be a testing factor for them, so answer it honestly. Do not give yourself extra credits or fewer credits. If you take extra credits, they might judge you on your skills afterward, and giving yourself fewer credits may give them the impression that you are not good in the software and may even half-mindedly move further. So be sure to give accurate points to yourself. 

Give some major differences between HTML and XML.

HTML stands for Hypertext Markup Language, whereas XML is Extensive Markup Language. HTML is used as a language to design the appearance or the look of the data on the screen. In contrast to this, XML can be either software or hardware used to store or transmit data. The main markup language is HTML, whereas XML only provides a framework for the markup languages. The case-sensitivity of the language also differs from HTML to XML, where HTML is not case sensitive. HTML also differs in how they are used, HTML is a presentation language, and XML represents neither presentation nor programming language.

Tell us some benefits of XML.

XML has various benefits due to its versatile and flexible nature to store, transmit and use data. Some of them are stated below:

  • Simplicity: The language is easy to use because it is both human and machine-readable. This makes it simple and a good option to be used.
  • Openness: W3C standard was given to it in 2010, which means that it was used/ endorsed by the big multinational software companies who were the market leaders.
  • Extensibility: The language is extensible, which means there is no set of fixed tags on how to use it and can be used according to the application to be developed or when there is a need for it.
  • Self-descriptive: Special schemas like traditional databases are not required in XML for the storage of data. They contain metadata in the form of attributes and tags, which removes the need for such definitions for data storage.
  • Scalable: Files can be edited and created in any file because it is not in binary form, making it easy to debug.
  • Fast Access: Due to storing data, it is easier and faster to access data. The pattern of storing data is hierarchical.

Define SAX in XML.

SAX (Simple API for XML) is used for parsing documents with the help of an API made by the XML-DEV mailing list. It is an event-driven online algorithm. The mechanism to read a document is provided by the SAX, which is also an alternative to the Document Object Model, which logically gives the structure of a document. The main difference between the two is DOM works on the whole of the document or builds an abstract syntax tree of the document, whereas the SAX works on the part of the document at one time, which is sequential. In simpler words, parsing events are issued, which makes a single pass through the input event. SAX is state-independent, whereas DOM is state-dependent which means there is no formal specification for SAX.

The main benefit of using this is minimum memory usage due to its parsing of event mechanisms. Only useful information is kept through the events, and the other part of the event is ended or reported. Maximum data involved and a maximum depth of the XML document is directly proportional to the minimum memory used. It is a faster and easier way to index, convert to other forms, format, sort, rearrange, etc., because of being event-driven, which only applies if the processing can be done in start-to-end format. Every coin has two sides. The disadvantage of using this is that some attributes or tags require access to the whole of the data to function properly, like in XSLT and XPath. 

Tell us your definition of a well-formed or valid XML document.

Synthetically correct and structurally correct documents are known as well-formed and valid documents, respectively. A well-formed document means that it abides by the basic rules of syntax. Valid documents stick to a set of predefined rules for a particular type of document, which means that they tell the type of data stored in each document. The rules are either written by the author of the document or by someone else.

Some of the basic rules for a well-formed document are as follows:

  • The closing tag is a necessity. 
  • The opening, as well as closing tag, must match in terms of case sensitivity also.
  • A single root tag must include all the elements of a document.
  • Parent tag is the higher class, and as XML follows hierarchical logic, all child elements must be closed before closing a parent class.
  • There must be zero or one colon in all the elements and attributes.
  • Values of attributes must be quoted.

What is Xpath and tell us one or two of its expressions?

For the selection of nodes in XML, XPath query language is used. It can also retrieve content or values ( String or Boolean) from an XML document. The World Wide Web Consortium has recommended using this and is defined by them.

  • It navigates through attributes and elements in XML documents.
  • It is a syntax for defining parts.
  • The path expression is used for navigation.
  • A standard function library is included in it.
  • XSLT and XQuery have it as a major element.
  • Consider a document library that contains different books which are to be searched or navigated. For this, a set of queries of XPath can be used, some of which are as follows:- 
  • /library/book[1] – The first child of the library element that is the first book element is selected.
  • /library/book[position()<3] – All the book elements are selected that have an index less than three in the child of the library element.

Since you said that XPath is a major element of XSLT, please define it.

XSLT is the transformation language of XML which stands for Extensible Spreadsheet Language Transformation, and uses XPath to navigate the document. It can convert XML documents into XML or other format documents like HTML for web pages, plain pages, etc., which can be subsequently converted into pdf, PNG, etc.

The working of XSLT is to create a new document from the data of the existing ones rather than updating the previous one. The input is mostly XML files, but it can intake anything which can build an XQuery or Xpath model like a geographical information system. Arbitrary computation can be done because language is theoretically complete, whereas it was only designed as a transformation language of XML. XQuery and XSLT have almost the same implications, but it has a higher hand on the features provided at a lower version.

Can graphics be used in the XML document. If yes, tell us with an example.

XLink and XPointer specifications can be used in XML for the use of graphics which are W3C recommendations. The creation of hyperlinks can be done by the use of XLink within XML documents. The elements behave like a link, and the linked files can or cannot have the defined links. The disadvantage of using this is that it doesn’t support browsers. The syntax or to access the XLink features XLink namespace has to be used. Some XLink attribute references are as follows:-

  • xlink:href – The URL of the web to be linked is given.
  • xlink: show – Defines the position of opening the link whose default is “replace.”
  • xlink: type – The type of the link is defined

As the name suggests, XPointer is used to point to a part of the XML document. Along with this, it uses XPath to navigate the XML document. It can be used in different XML languages but is not supported by the browsers. The XPointer can be used by adding a number sign (#) and a URL of the XLink pointer.

Example of XLink:



xlink :href=”http://book.com/library.gif”

xlink:show =”new”>



Can conditional statements be used in the XML document?

Unlike programming languages, we cannot use conditional statements directly. Document Type Definition (DTD) has to be used. A set of markup declarations that define a document type is known as DTD or Document Type Definition. The valid blocks to build an XML document are defined by DTD means it defines the validated list and elements which can be used in the document.


  • <foo if{DB}=”a”>bar</foo>
  • <xsl:if test=”@foo=’book’ ”> <xsl:text> Hello, world!</xsl:text></xsl:if>

Tell us about the nested elements.

Inside the root element, if there are more than two or more elements, then they are known as nested elements in XML. They are easy and faster to use because they make a hierarchy and keep an XML document in check.

Learning a new language is always helpful in the long run. XML, due to its versatile nature, is easy to learn and implement. Although it may not be a presentation language, it provides some graphics for use. It also provides most of the utilities and features which are required for storing and transporting data. It is advisable to learn XML for the front-end and back-end development to make it easy and feasible.

XML Interview Questions

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