Test your skills through the online practice test: XML Quiz Online Practice Test

Related differences

HTML vs XMLJSON vs XML

Ques 21. When constructing an XML DTD, how do you create an external entity reference in an attribute value?

Every interview session should have at least one trick question. Although possible when using SGML, XML DTDs don't support defining external entity references in attribute values. It's more important for the candidate to respond to this question in a logical way than than the candidate know the somewhat obscure answer.

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Ques 22. What is the difference between XML and C or C++ or Java?

C and C++ (and other languages like FORTRAN, or Pascal, or Visual Basic, or Java or hundreds more) are programming languages with which you specify calculations, actions, and decisions to be carried out in order: mod curconfig[if left(date,6) = "01-Apr", t.put "April googlel!", f.put days('31102005','DDMMYYYY') - days(sdate,'DDMMYYYY') " more shopping days to Samhain"];
XML is a markup specification language with which you can design ways of describing information (text or data), usually for storage, transmission, or processing by a program. It says nothing about what you should do with the data (although your choice of element names may hint at what they are for):
<part num="DA42" models="LS AR DF HG KJ" update="2001-11-22">
<name>Camshaft end bearing retention circlip</name>
<image drawing="RR98-dh37" type="SVG" x="476" y="226"/> <maker id="RQ778">Ringtown Fasteners Ltd</maker>
<notes>Angle-nosed insertion tool <tool id="GH25"/> is required for the removal and replacement of this part.</notes>
</part>
On its own, an SGML or XML file (including HTML) doesn't do anything. It's a data format which just sits there until you run a program.

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Ques 23. Does XML replace HTML?

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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Ques 24. Do I have to know HTML or SGML before I learn XML?

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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Ques 25. What does an XML document actually look like (inside)?

The basic structure of XML is similar to other applications of SGML, including HTML. The basic components can be seen in the following examples.
An XML document starts with a Prolog:
1. The XML Declaration

which specifies that this is an XML document;
2. Optionally a Document Type Declaration

which identifies the type of document and says where the Document Type Description (DTD) is stored;
The Prolog is followed by the document instance:
1. A root element, which is the outermost (top level) element (start-tag plus end-tag) which encloses everything else: in the examples below the root elements are conversation and titlepage;
2. A structured mix of descriptive or prescriptive elements enclosing the character data content (text), and optionally any attributes (?name=value? pairs) inside some start-tags. XML documents can be very simple, with straightforward nested markup of your own design.

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