Below are some important XML interview questions which are asked in most MNC company interviews for beginners or professionals.
11. Why not just carry on extending HTML?
HTML was already overburdened with dozens of interesting but incompatible inventions from different manufacturers, because it provides only one way of describing your information. XML allows groups of people or organizations to question C.13, create their own customized markup applications for exchanging information in their domain (music, chemistry, electronics, hill-walking, finance, surfing, petroleum geology, linguistics, cooking, knitting, stellar cartography, history, engineering, rabbit-keeping, question C.19, mathematics, genealogy, etc). HTML is now well beyond the limit of its usefulness as a way of describing information, and while it will continue to play an important role for the content it currently represents, many new applications require a more robust and flexible infrastructure.
12. Why should I use XML?
Here are a few reasons for using XML (in no particular order). Not all of these will apply to your own requirements, and you may have additional reasons not mentioned here (if so, please let the editor of the FAQ know!).
* XML can be used to describe and identify information accurately and unambiguously, in a way that computers can be programmed to ‘understand’ (well, at least manipulate as if they could understand).
* XML allows documents which are all the same type to be created consistently and without structural errors, because it provides a standardised way of describing, controlling, or allowing/disallowing particular types of document structure. [Note that this has absolutely nothing whatever to do with formatting, appearance, or the actual text content of your documents, only the structure of them.]
* XML provides a robust and durable format for information storage and transmission. Robust because it is based on a proven standard, and can thus be tested and verified; durable because it uses plain-text file formats which will outlast proprietary binary ones.
* XML provides a common syntax for messaging systems for the exchange of information between applications. Previously, each messaging system had its own format and all were different, which made inter-system messaging unnecessarily messy, complex, and expensive. If everyone uses the same syntax it makes writing these systems much faster and more reliable.
* XML is free. Not just free of charge (free as in beer) but free of legal encumbrances (free as in speech). It doesn't belong to anyone, so it can't be hijacked or pirated. And you don't have to pay a fee to use it (you can of course choose to use commercial software to deal with it, for lots of good reasons, but you don't pay for XML itself).
* XML information can be manipulated programmatically (under machine control), so XML documents can be pieced together from disparate sources, or taken apart and re-used in different ways. They can be converted into almost any other format with no loss of information.
* XML lets you separate form from content. Your XML file contains your document information (text, data) and identifies its structure: your formatting and other processing needs are identified separately in a stylesheet or processing system. The two are combined at output time to apply the required formatting to the text or data identified by its structure (location, position, rank, order, or whatever).
Can you walk us through the steps necessary to parse XML documents?
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.
Give some examples of XML DTDs or schemas that you have worked with.
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 for a particular project where no standard existed.
13. Using XSLT, how would you extract a specific attribute from an element in an XML document?
Successful candidates should recognize this as one of the most basic applications of XSLT. If they are not able to construct a reply similar to the example below, they should at least be able to identify the components necessary for this operation: xsl:template to match the appropriate XML element, xsl:value-of to select the attribute value, and the optional xsl:apply-templates to continue processing the document.
Extract Attributes from XML Data
Example 1.
<xsl:template match="element-name">
Attribute Value:
<xsl:value-of select="@attribute"/>
<xsl:apply-templates/>
</xsl:template>
14. 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.
15. How would you build a search engine for large volumes of XML data?
The way candidates answer this question may provide insight into their view of XML data. For those who view XML primarily as a way to denote structure for text files, a common answer is to build a full-text search and handle the data similarly to the way Internet portals handle HTML pages. Others consider XML as a standard way of transferring structured data between disparate systems. These candidates often describe some scheme of importing XML into a relational or objectdatabase and relying on the database's engine for searching. Lastly, candidates that have worked with vendors specializing in this area often say that the best way the handle this situation is to use a third party software package optimized for XML data.
16. 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 which does something with it.
17. 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.)
18. 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.
19. 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:
<?xml version="1.0" standalone="yes"?>
<conversation><br>
<greeting>Hello, world!</greeting>
<response>Stop the planet, I want to get
off!</response>
</conversation>
Or they can be more complicated, with a Schema or question C.11, Document Type Description (DTD) or internal subset (local DTD changes in [square brackets]), and an arbitrarily complex nested structure:
<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE titlepage
SYSTEM "http://www.google.bar/dtds/typo.dtd"
[<!ENTITY % active.links "INCLUDE">]>
<titlepage id="BG12273624">
<white-space type="vertical" amount="36"/>
<title font="Baskerville" alignment="centered"
size="24/30">Hello, world!</title>
<white-space type="vertical" amount="12"/>
<!-- In some copies the following
decoration is hand-colored, presumably
by the author -->
<image location="http://www.google.bar/fleuron.eps"
type="URI" alignment="centered"/>
<white-space type="vertical" amount="24"/>
<author font="Baskerville" size="18/22"
style="italic">Vitam capias</author>
<white-space type="vertical" role="filler"/>
</titlepage>
Or they can be anywhere between: a lot will depend on how you want to define your document type (or whose you use) and what it will be used for. Database-generated or program-generated XML documents used in e-commerce is usually unformatted (not for human reading) and may use very long names or values, with multiple redundancy and sometimes no character data content at all, just values in attributes:
<?xml version="1.0"?> <ORDER-UPDATE AUTHMD5="4baf7d7cff5faa3ce67acf66ccda8248"
ORDER-UPDATE-ISSUE="193E22C2-EAF3-11D9-9736-CAFC705A30B3"
ORDER-UPDATE-DATE="2005-07-01T15:34:22.46" ORDER-UPDATE-DESTINATION="6B197E02-EAF3-11D9-85D5-997710D9978F"
ORDER-UPDATE-ORDERNO="8316ADEA-EAF3-11D9-9955-D289ECBC99F3">
<ORDER-UPDATE-DELTA-MODIFICATION-DETAIL ORDER-UPDATE-ID="BAC352437484">
<ORDER-UPDATE-DELTA-MODIFICATION-VALUE ORDER-UPDATE-ITEM="56"
ORDER-UPDATE-QUANTITY="2000"/>
</ORDER-UPDATE-DELTA-MODIFICATION-DETAIL>
</ORDER-UPDATE>
20. How does XML handle white-space in my documents?
All white-space, including linebreaks, TAB characters, and normal spaces, even between ‘structural’ elements where no text can ever appear, is passed by the parser unchanged to the application (browser, formatter, viewer, converter, etc), identifying the context in which the white-space was found (element content, data content, or mixed content, if this information is available to the parser, eg from a DTD or Schema). This means it is the application's responsibility to decide what to do with such space, not the parser's:
* insignificant white-space between structural elements (space which occurs where only element content is allowed, ie between other elements, where text data never occurs) will get passed to the application (in SGML this white-space gets suppressed, which is why you can put all that extra space in HTML documents and not worry about it)
* significant white-space (space which occurs within elements which can contain text and markup mixed together, usually mixed content or PCDATA) will still get passed to the application exactly as under SGML. It is the application's responsibility to handle it correctly.
The parser must inform the application that white-space has occurred in element content, if it can detect it. (Users of SGML will recognize that this information is not in the ESIS, but it is in the Grove.)
<chapter>
<title>
My title for
Chapter 1.
</title>
<para>
text
</para>
</chapter>
In the example above, the application will receive all the pretty-printing linebreaks, TABs, and spaces between the elements as well as those embedded in the chapter title. It is the function of the application, not the parser, to decide which type of white-space to discard and which to retain. Many XML applications have configurable options to allow programmers or users to control how such white-space is handled.
More Questions & Answers :-
Part1 Part2 Part3 Part4 Part5 Part6
11. Why not just carry on extending HTML?
HTML was already overburdened with dozens of interesting but incompatible inventions from different manufacturers, because it provides only one way of describing your information. XML allows groups of people or organizations to question C.13, create their own customized markup applications for exchanging information in their domain (music, chemistry, electronics, hill-walking, finance, surfing, petroleum geology, linguistics, cooking, knitting, stellar cartography, history, engineering, rabbit-keeping, question C.19, mathematics, genealogy, etc). HTML is now well beyond the limit of its usefulness as a way of describing information, and while it will continue to play an important role for the content it currently represents, many new applications require a more robust and flexible infrastructure.
12. Why should I use XML?
Here are a few reasons for using XML (in no particular order). Not all of these will apply to your own requirements, and you may have additional reasons not mentioned here (if so, please let the editor of the FAQ know!).
* XML can be used to describe and identify information accurately and unambiguously, in a way that computers can be programmed to ‘understand’ (well, at least manipulate as if they could understand).
* XML allows documents which are all the same type to be created consistently and without structural errors, because it provides a standardised way of describing, controlling, or allowing/disallowing particular types of document structure. [Note that this has absolutely nothing whatever to do with formatting, appearance, or the actual text content of your documents, only the structure of them.]
* XML provides a robust and durable format for information storage and transmission. Robust because it is based on a proven standard, and can thus be tested and verified; durable because it uses plain-text file formats which will outlast proprietary binary ones.
* XML provides a common syntax for messaging systems for the exchange of information between applications. Previously, each messaging system had its own format and all were different, which made inter-system messaging unnecessarily messy, complex, and expensive. If everyone uses the same syntax it makes writing these systems much faster and more reliable.
* XML is free. Not just free of charge (free as in beer) but free of legal encumbrances (free as in speech). It doesn't belong to anyone, so it can't be hijacked or pirated. And you don't have to pay a fee to use it (you can of course choose to use commercial software to deal with it, for lots of good reasons, but you don't pay for XML itself).
* XML information can be manipulated programmatically (under machine control), so XML documents can be pieced together from disparate sources, or taken apart and re-used in different ways. They can be converted into almost any other format with no loss of information.
* XML lets you separate form from content. Your XML file contains your document information (text, data) and identifies its structure: your formatting and other processing needs are identified separately in a stylesheet or processing system. The two are combined at output time to apply the required formatting to the text or data identified by its structure (location, position, rank, order, or whatever).
Can you walk us through the steps necessary to parse XML documents?
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.
Give some examples of XML DTDs or schemas that you have worked with.
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 for a particular project where no standard existed.
13. Using XSLT, how would you extract a specific attribute from an element in an XML document?
Successful candidates should recognize this as one of the most basic applications of XSLT. If they are not able to construct a reply similar to the example below, they should at least be able to identify the components necessary for this operation: xsl:template to match the appropriate XML element, xsl:value-of to select the attribute value, and the optional xsl:apply-templates to continue processing the document.
Extract Attributes from XML Data
Example 1.
<xsl:template match="element-name">
Attribute Value:
<xsl:value-of select="@attribute"/>
<xsl:apply-templates/>
</xsl:template>
14. 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.
15. How would you build a search engine for large volumes of XML data?
The way candidates answer this question may provide insight into their view of XML data. For those who view XML primarily as a way to denote structure for text files, a common answer is to build a full-text search and handle the data similarly to the way Internet portals handle HTML pages. Others consider XML as a standard way of transferring structured data between disparate systems. These candidates often describe some scheme of importing XML into a relational or objectdatabase and relying on the database's engine for searching. Lastly, candidates that have worked with vendors specializing in this area often say that the best way the handle this situation is to use a third party software package optimized for XML data.
16. 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 which does something with it.
17. 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.)
18. 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.
19. 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:
<?xml version="1.0" standalone="yes"?>
<conversation><br>
<greeting>Hello, world!</greeting>
<response>Stop the planet, I want to get
off!</response>
</conversation>
Or they can be more complicated, with a Schema or question C.11, Document Type Description (DTD) or internal subset (local DTD changes in [square brackets]), and an arbitrarily complex nested structure:
<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE titlepage
SYSTEM "http://www.google.bar/dtds/typo.dtd"
[<!ENTITY % active.links "INCLUDE">]>
<titlepage id="BG12273624">
<white-space type="vertical" amount="36"/>
<title font="Baskerville" alignment="centered"
size="24/30">Hello, world!</title>
<white-space type="vertical" amount="12"/>
<!-- In some copies the following
decoration is hand-colored, presumably
by the author -->
<image location="http://www.google.bar/fleuron.eps"
type="URI" alignment="centered"/>
<white-space type="vertical" amount="24"/>
<author font="Baskerville" size="18/22"
style="italic">Vitam capias</author>
<white-space type="vertical" role="filler"/>
</titlepage>
Or they can be anywhere between: a lot will depend on how you want to define your document type (or whose you use) and what it will be used for. Database-generated or program-generated XML documents used in e-commerce is usually unformatted (not for human reading) and may use very long names or values, with multiple redundancy and sometimes no character data content at all, just values in attributes:
<?xml version="1.0"?> <ORDER-UPDATE AUTHMD5="4baf7d7cff5faa3ce67acf66ccda8248"
ORDER-UPDATE-ISSUE="193E22C2-EAF3-11D9-9736-CAFC705A30B3"
ORDER-UPDATE-DATE="2005-07-01T15:34:22.46" ORDER-UPDATE-DESTINATION="6B197E02-EAF3-11D9-85D5-997710D9978F"
ORDER-UPDATE-ORDERNO="8316ADEA-EAF3-11D9-9955-D289ECBC99F3">
<ORDER-UPDATE-DELTA-MODIFICATION-DETAIL ORDER-UPDATE-ID="BAC352437484">
<ORDER-UPDATE-DELTA-MODIFICATION-VALUE ORDER-UPDATE-ITEM="56"
ORDER-UPDATE-QUANTITY="2000"/>
</ORDER-UPDATE-DELTA-MODIFICATION-DETAIL>
</ORDER-UPDATE>
20. How does XML handle white-space in my documents?
All white-space, including linebreaks, TAB characters, and normal spaces, even between ‘structural’ elements where no text can ever appear, is passed by the parser unchanged to the application (browser, formatter, viewer, converter, etc), identifying the context in which the white-space was found (element content, data content, or mixed content, if this information is available to the parser, eg from a DTD or Schema). This means it is the application's responsibility to decide what to do with such space, not the parser's:
* insignificant white-space between structural elements (space which occurs where only element content is allowed, ie between other elements, where text data never occurs) will get passed to the application (in SGML this white-space gets suppressed, which is why you can put all that extra space in HTML documents and not worry about it)
* significant white-space (space which occurs within elements which can contain text and markup mixed together, usually mixed content or PCDATA) will still get passed to the application exactly as under SGML. It is the application's responsibility to handle it correctly.
The parser must inform the application that white-space has occurred in element content, if it can detect it. (Users of SGML will recognize that this information is not in the ESIS, but it is in the Grove.)
<chapter>
<title>
My title for
Chapter 1.
</title>
<para>
text
</para>
</chapter>
In the example above, the application will receive all the pretty-printing linebreaks, TABs, and spaces between the elements as well as those embedded in the chapter title. It is the function of the application, not the parser, to decide which type of white-space to discard and which to retain. Many XML applications have configurable options to allow programmers or users to control how such white-space is handled.
More Questions & Answers :-
Part1 Part2 Part3 Part4 Part5 Part6
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