top 21-30 Giant list of XML interview questions and answers

continue:

21. What is the difference between XML and C or C++ or
Java? Updated

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.

22. 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.)

23. 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.

24. 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>

25. 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.

26. Which parts of an XML document are case-sensitive?

All of it, both markup and text. This is significantly different
from HTML and most other SGML applications. It was done to allow
markup in non-Latin-alphabet languages, and to obviate problems
with case-folding in writing systems which are caseless.
* Element type names are case-sensitive: you must follow whatever
combination of upper- or lower-case you use to define them (either
by first usage or in a DTD or Schema). So you can’t say <BODY>Ã¢â‚¬Â¦</body>:
upper- and lower-case must match; thus <Img/>, <IMG/>,
and <img/> are three different element types;

* For well-formed XML documents with no DTD, the first occurrence
of an element type name defines the casing;
* Attribute names are also case-sensitive, for example the two width
attributes in <PIC width=”7in”/> and <PIC WIDTH=”6in”/>
(if they occurred in the same file) are separate attributes, because
of the different case of width and WIDTH;
* Attribute values are also case-sensitive. CDATA values (eg Url=”MyFile.SGML”)
always have been, but NAME types (ID and IDREF attributes, and token
list attributes) are now case-sensitive as well;
* All general and parameter entity names (eg A), and your
data content (text), are case-sensitive as always.

27. How can I make my existing HTML files work in XML?

Either convert them to conform to some new document type (with
or without a DTD or Schema) and write a stylesheet to go with them;
or edit them to conform to XHTML. It is necessary to convert existing
HTML files because XML does not permit end-tag minimisation (missing
, etc), unquoted attribute values, and a number of other SGML shortcuts
which have been normal in most HTML DTDs. However, many HTML authoring
tools already produce almost (but not quite) well-formed XML.
You may be able to convert HTML to XHTML using the Dave Raggett’s
HTML Tidy program, which can clean up some of the formatting mess
left behind by inadequate HTML editors, and even separate out some
of the formatting to a stylesheet, but there is usually still some
hand-editing to do.

28. Is there an XML version of HTML?

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 small set of guidelines (see
the W3C site).

29. If XML is just a subset of SGML, can I use XML files
directly with existing SGML tools?

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 DTDless XML
file. Most SGML tools now handle XML files well, and provide an
option switch between the two standards.

30. Can XML use non-Latin characters?

Yes, the XML Specification explicitly says XML uses ISO 10646,
the international standard character repertoire which covers most
known languages. Unicode is an identical repertoire, and the two
standards track each other. The spec says (2.2): ‘All XML
processors must accept the UTF-8 and UTF-16 encodings of ISO 10646Ã¢â‚¬Â¦’.
There is a Unicode FAQ at http://www.unicode.org/faq/FAQ.
UTF-8 is an encoding of Unicode into 8-bit characters: the first
128 are the same as ASCII, and higher-order characters are used
to encode anything else from Unicode into sequences of between 2
and 6 bytes. UTF-8 in its single-octet form is therefore the same
as ISO 646 IRV (ASCII), so you can continue to use ASCII for English
or other languages using the Latin alphabet without diacritics.
Note that UTF-8 is incompatible with ISO 8859-1 (ISO Latin-1) after
code point 127 decimal (the end of ASCII).
UTF-16 is an encoding of Unicode into 16-bit characters, which lets
it represent 16 planes. UTF-16 is incompatible with ASCII because
it uses two 8-bit bytes per character (four bytes above U+FFFF).