Technical interview questions and answers are crucial in XML Interviews because XML is widely used for data storage, configuration, API communication, and document structuring. Many companies use XML as a standard format in web applications, making it an important topic in technical interviews. Companies like TCS, Wipro, Infosys, Cognizant, and Accenture often ask XML questions to check whether candidates understand syntax, DTD, XSD, parsing, and real-time use cases. This guide provides fully solved XML interview questions with simple explanations suitable for freshers, students, and job seekers. These questions will help you perform confidently in technical rounds and placement interviews.
Web developers working with markup languages should strengthen their foundation in HTML structure and XHTML standards for document formatting
1. What is XML?
Answer: XML is the Extensible Markup Language. It improves the functionality of the Web by letting you identify your information in a more accurate, flexible, and adaptable way.
It is extensible because it is not a fixed format like HTML (which is a single, predefined markup language). Instead, XML is actually a metalanguage—a language for describing other languages—which lets you design your own markup languages for limitless different types of documents. XML can do this because it's written in SGML,
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2. What is a markup language?
Answer: A markup language is a set of words and symbols for describing the identity of pieces of a document (for example ‘this is a paragraph, ‘this is a heading, ‘this is a list, ‘this is the caption of this figure, etc). Programs can use this with a style sheet to create output for screen, print, audio, video, Braille, etc.
Some markup languages (e.g. those used in word processors) only describe appearances (‘this is italics, ‘this is bold), but this method can only be used for display, and is
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3. Why is XML such an important development?
Answer: It removes two constraints which were holding back Web developments:
1. dependence on a single, inflexible document type (HTML) which was being much abused for tasks it was never designed for;
2. the complexity of full SGML, whose syntax allows many powerful but hard-to-program options.
XML allows the flexible development of user-defined document types. It provides a robust, non-proprietary, persistent, and verifiable file format for the storage and transmission of text and data both on and o
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4. Describe the role that XSL can play when dynamically generating HTML pages from a relational database.
Answer: Even if candidates have never participated in a project involving this type of architecture, they should recognize it as one of the common uses of XML. Querying a database and then formatting the result set so that it can be validated as an XML document allows developers to translate the data into an HTML table using XSLT rules. Consequently, the format of the resulting HTML table can be modified without changing the database query or application code since the document rendering logic is isolat
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5. Who is responsible for XML?
Answer: XML is a project of the World Wide Web Consortium (W3C), and the development of the specification is supervised by an XML Working Group. A Special Interest Group of co-opted contributors and experts from various fields contributed comments and reviews by email.
XML is a public format: it is not a proprietary development of any company, although the membership of the WG and the SIG represented companies as well as research and academic institutions. The v1.0 specification was accepted by the W3
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6. Why is XML such an important development?
Answer: It removes two constraints which were holding back Web developments:
1. dependence on a single, inflexible document type (HTML) which was being much abused for tasks it was never designed for;
2. the complexity of full question A.4, SGML, whose syntax allows many powerful but hard-to-program options.
XML allows the flexible development of user-defined document types. It provides a robust, non-proprietary, persistent, and verifiable file format for the storage and transmission of text and da
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7. What is DOM and how does it relate to XML?
Answer: The Document Object Model (DOM) is an interface specification maintained by the W3C DOM Workgroup that defines an application independent mechanism to access, parse, or update XML data. In simple terms it is a hierarchical model that allows developers to manipulate XML documents easily Any developer that has worked extensively with XML should be able to discuss the concept and use of DOM objects freely. Additionally, it is not unreasonable to expect advanced candidates to thoroughly understand i
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8. What is SOAP and how does it relate to XML?
Answer: The Simple Object Access Protocol (SOAP) uses XML to define a protocol for the exchange of information in distributed computing environments. SOAP consists of three components: an envelope, a set of encoding rules, and a convention for representing remote procedure calls. Unless experience with SOAP is a direct requirement for the open position, knowing the specifics of the protocol, or how it can be used in conjunction with HTTP, is not as important as identifying it as a natural application of
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9. Can you walk us through the steps necessary to parse XML documents?
Answer: Superficially, this is a fairly basic question. However, the point is not to determine whether candidates understand the concept of a parser but rather have them walk through the process of parsing XML documents step-by-step. Determining whether a non-validating or validating parser is needed, choosing the appropriate parser, and handling errors are all important aspects to this process that should be included in the candidate's response.
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10. Give some examples of XML DTDs or schemas that you have worked with.
Answer: Although XML does not require data to be validated against a DTD, many of the benefits of using the technology are derived from being able to validate XML documents against business or technical architecture rules. Polling for the list of DTDs that developers have worked with provides insight to their general exposure to the technology. The ideal candidate will have knowledge of several of the commonly used DTDs such as FpML, DocBook, HRML, and RDF, as well as experience designing a custom DTD f
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11. Does XML replace HTML?
Answer: No. XML itself does not replace HTML. Instead, it provides an alternative which allows you to define your own set of markup elements. HTML is expected to remain in common use for some time to come, and the current version of HTML is in XML syntax. XML is designed to make the writing of DTDs much simpler than with full SGML. (See the question on DTDs for what one is and why you might want one.)
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12. Do I have to know HTML or SGML before I learn XML?
Answer: No, although it's useful because a lot of XML terminology and practice derives from two decades' experience of SGML.
Be aware that ‘knowing HTML is not the same as ‘understanding SGML. Although HTML was written as an SGML application, browsers ignore most of it (which is why so many useful things don't work), so just because something is done a certain way in HTML browsers does not mean it's correct, least of all in XML.
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13. Is there an XML version of HTML?
Answer: Yes, the W3C recommends using XHTML which is ‘a reformulation of HTML 4 in XML 1.0. This specification defines HTML as an XML application, and provides three DTDs corresponding to the ones defined by HTML 4.* (Strict, Transitional, and Frameset).
The semantics of the elements and their attributes are as defined in the W3C Recommendation for HTML 4. These semantics provide the foundation for future extensibility of XHTML. Compatibility with existing HTML browsers is possible by following a sma
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14. If XML is just a subset of SGML, can I use XML files directly with existing SGML tools?
Answer: Yes, provided you use up-to-date SGML software which knows about the WebSGML Adaptations TC to ISO 8879 (the features needed to support XML, such as the variant form for EMPTY elements; some aspects of the SGML Declaration such as NAMECASE GENERAL NO; multiple attribute token list declarations, etc).
An alternative is to use an SGML DTD to let you create a fully-normalised SGML file, but one which does not use empty elements; and then remove the DocType Declaration so it becomes a well-formed
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15. Does XML let me make up my own tags?
Answer: No, it lets you make up names for your own element types. If you think tags and elements are the same thing you are already in considerable trouble: read the rest of this question carefully.
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16. How do I create my own document type?
Answer: Document types usually need a formal description, either a DTD or a Schema. Whilst it is possible to process well-formed XML documents without any such description, trying to create them without one is asking for trouble. A DTD or Schema is used with an XML editor or API interface to guide and control the construction of the document, making sure the right elements go in the right places.
Creating your own document type therefore begins with an analysis of the class of documents you want to de
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17. Can a root element type be explicitly declared in the DTD?
Answer: No. This is done in the document's Document Type Declaration, not in the DTD.
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18. How does XML handle metadata?
Answer: Because XML lets you define your own markup languages, you can make full use of the extended hypertext features of XML (see the question on Links) to store or link to metadata in any format (eg using ISO 11179, as a Topic Maps Published Subject, with Dublin Core, Warwick Framework, or with Resource Description Framework (RDF), or even Platform for Internet Content Selection (PICS)).
There are no predefined elements in XML, because it is an architecture, not an application, so it is not part of
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19. Can I use Java to create or manage XML files?
Answer: Yes, any programming language can be used to output data from any source in XML format. There is a growing number of front-ends and back-ends for programming environments and data management environments to automate this. Java is just the most popular one at the moment.
There is a large body of middleware (APIs) written in Java and other languages for managing data either in XML or with XML input or output.
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20. Can I still use server-side inclusions?
Answer: Yes, so long as what they generate ends up as part of an XML-conformant file (ie either valid or just well-formed).
Server-side tag-replacers like shtml, PHP, JSP, ASP, Zope, etc store almost-valid files using comments, Processing Instructions, or non-XML markup, which gets replaced at the point of service by text or XML markup (it is unclear why some of these systems use non-HTML/XML markup). There are also some XML-based preprocessors for formats like XVRL (eXtensible Value Resolution Langua
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21. Can I (and my authors) still use client-side inclusions?
Answer: The same rule applies as for server-side inclusions, so you need to ensure that any embedded code which gets passed to a third-party engine (eg calls to SQL, VB, Java, etc) does not contain any characters which might be misinterpreted as XML markup (ie no angle brackets or ampersands). Either use a CDATA marked section to avoid your XML application parsing the embedded code, or use the standard <, and & character entity references instead.
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22. Do XML namespaces apply to entity names, notation names, or processing instruction targets?
Answer: No.
XML namespaces apply only to element type and attribute names. Furthermore, in an XML document that conforms to the XML namespaces recommendation, entity names, notation names, and processing instruction targets must not contain colons.
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23. Who can create an XML namespace?
Answer: Anybody can create an XML namespace -- all you need to do is assign a URI as its name and decide what element type and attribute names are in it. The URI must be under your control and should not be being used to identify a different XML namespace, such as by a coworker.
(In practice, most people that create XML namespaces also describe the element types and attributes whose names are in it -- their content models and types, their semantics, and so on. However, this is not part of the process
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24. Where can I declare an XML namespace?
Answer: You can declare an XML namespace on any element in an XML document. The namespace is in scope for that element and all its descendants unless it is overridden.
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25. How can I declare XML namespaces so that all elements and attributes are in their scope?
Answer: XML namespace declarations that are made on the root element are in scope for all elements and attributes in the document. This means that an easy way to declare XML namespaces is to declare them only on the root element
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26. Does the scope of an XML namespace declaration ever include the DTD?
Answer: No.
XML namespaces can be declared only on elements and their scope consists only of those elements and their descendants. Thus, the scope can never include the DTD.
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27. Do XML namespace declarations apply to DTDs?
Answer: No.
In particular, an xmlns attribute declared in the DTD with a default is not an XML namespace declaration for the DTD.. (Note that an earlier version of MSXML (the parser used by Internet Explorer) did use such declarations as XML namespace declarations, but that this was removed in MSXML 4.
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28. How do I create documents that use XML namespaces?
Answer: The same as you create documents that don't use XML namespaces. If you're currently using Notepad on Windows or emacs on Linux, you can continue using Notepad or emacs. If you're using an XML editor that is not namespace-aware, you can also continue to use that, as qualified names are legal names in XML documents and xmlns attributes are legal attributes. And if you're using an XML editor that is namespace-aware, it will probably provide features such as automatically declaring XML namespaces an
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29. What software is needed to process XML namespaces?
Answer: From a document author's perspective, this is generally not a relevant question. Most XML documents are written in a specific XML language and processed by an application that understands that language. If the language uses an XML namespace, then the application will already use that namespace -- there is no need for any special XML namespace software.
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30. What does a namespace-aware application do when it encounters an error?
Answer: The XML namespaces recommendation does not specify what a namespace-aware application does when it encounters a document that does not conform to the recommendation. Therefore, the behavior is application-dependent. For example, the application could stop processing, post an error to a log and continue processing, or ignore the error.
PART III: NAMES, PREFIXES, AND URIs
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31. What characters are allowed in a qualified name?
Answer: The prefix can contain any character that is allowed in the Name [5] production in XML 1.0 except a colon. The same is true of the local name. Thus, there can be at most one colon in a qualified name -- the colon used to separate the prefix from the local name.
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32. What is an XML namespace prefix?
Answer: An XML namespace prefix is a prefix used to specify that a local element type or attribute name is in a particular XML namespace. For example, in the following, the serv prefix specifies that the Address element type name is in the http://www.foo.com/ito/addresses namespace:
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33. What characters are allowed in an XML namespace prefix?
Answer: The prefix can contain any character that is allowed in the Name [5] production in XML 1.0 except a colon.
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35. What happens if there is no prefix on an element type name?
Answer: If a default XML namespace declaration is in scope, then the element type name is in the default XML namespace. Otherwise, the element type name is not in any XML namespace.
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36. What is an XML namespace name?
Answer: An XML namespace name is a URI that uniquely identifies the namespace. URIs are used because they are widely understood and well documented. Because people may only allocate URIs under their control, it is easy to ensure that no two XML namespaces are identified by the same URI.
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38. Can I use a relative URI as a namespace name?
Answer: Yes. However, such usage is deprecated, so you should never do it.
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39. How do I configure an XPointer processor?
Answer: There is no required configuration for the XPointer Framework. The uberjar command line utility provides some configuration options. Applications configure individual XPointer processors when they obtain an instance from an appropriate XPointerProcessor factory method.
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40. What three essential components of security does the XML Signatures provide?
Answer: authentication, message integrity, and non-repudiation. In addition to signature information, an XML Signature can also contain information describing the key used to sign the content.
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