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Describe the differences between XML and HTML.
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It's amazing how many developers
claim to be proficient programming with XML, yet do not understand the
basic differences between XML and HTML. Anyone with a fundamental grasp
of XML should be able describe some of the main differences outlined in
the table below.
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Differences
Between XML and HTML
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| XML |
HTML |
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User definable tags
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Defined set of tags designed for web display
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Content driven
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Format driven
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End tags required for well formed documents
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End tags not required
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Quotes required around attributes values
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Quotes not required
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Slash required in empty tags
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Slash not required
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Describe
the role that XSL can play when dynamically generating HTML pages from
a relational database.
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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 isolated to the
XSLT rules.
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Give
a few examples of types of applications that can benefit from using
XML.
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There are literally thousands of
applications that can benefit from XML technologies. The point of this
question is not to have the candidate rattle off a laundry list of
projects that they have worked on, but, rather, to allow the candidate
to explain the rationale for choosing XML by citing a few real world
examples. For instance, one appropriate answer is that XML allows
content management systems to store documents independently of their
format, which thereby reduces data redundancy. Another answer relates
to B2B exchanges or supply chain management systems. In these
instances, XML provides a mechanism for multiple companies to exchange
data according to an agreed upon set of rules. A third common response
involves wireless applications that require WML to render data on hand
held devices.
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What
is DOM and how does it relate to XML?
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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 its internal
workings and be able to explain how DOM differs from an event-based
interface like SAX.
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What
is SOAP and how does it relate to XML?
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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
XML.
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Can
you walk us through the steps necessary to parse XML documents?
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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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Give
some examples of XML DTDs or schemas that you have worked with.
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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.
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Using
XSLT, how would you extract a specific attribute from an element in an
XML document?
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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>
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When
constructing an XML DTD, how do you create an external entity reference
in an attribute value?
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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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How
would you build a search engine for large volumes of XML data?
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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 object database 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.
Obviously, some important areas of XML technologies were not included
in this list -- namespaces, XPointer, XLink, and so on -- and should be
added to the interviewer's set of questions if applicable to the
particular position that the candidate is applying for. However, these
questions in conjunction with others to assess soft skills
(communication skills, ability to work on teams, leadership ability,
etc.) will help determine how well candidates understand the
fundamental principles of XML.
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Why
is XML such an important development?
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It removes two constraints which
were holding back Web developments:<br> 1. § dependence on a
single, inflexible document type (HTML) which was being much abused for
tasks it was never designed for;<br> 2. the complexity of full
SGML, whose syntax allows many powerful but hard-to-program
options.<br> § 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 off the Web; and it removes the more
complex options of SGML, making it easier to program for.
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Is
it possible to write the contents of org.w3c.dom.Document object into
an .xml file?
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Yes its possible. One to achieve
this is by using Xerces. Xerces is an XML parser. You would use the
following code
org.apache.xml.serialize.OutputFormat format = new
org.apache.xml.serialize.OutputFormat(myDocument);
org.apache.xml.serialize.XMLSerializer output = new
org.apache.xml.serialize.XMLSerializer(new FileOutputStream(new
File("test.xml")), format);
output.serialize(myDocument);
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What
is the difference between DOM and SAX? What would you use if an option
is given?
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DOM parses an XML document and
returns an instance of org.w3c.dom.Document. This document object's
tree must then
be "walked" in order to process the different elements. DOM parses the
ENTIRE Document into memory, and then makes it
available to you. The size of the Document you can parse is limited to
the memory available.
SAX uses an event callback mechanism requiring you to code methods to
handle events thrown by the parser as it
encounters different entities within the XML document. SAX throws
events as the Document is being parsed. Only the
current element is actually in memory, so there is no limit to the size
of a Document when using SAX.
The specific parser technology that will be used will be determined by
the requirements of your application. If you need the
entire document represented, you will most likely use DOM builder
implementation. If you only care about parts of the
XML document and/or you only need to parse the document once, you might
be better served using SAX implementation.
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What
is SOAP?
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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.
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What
is DOM?
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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.
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Can
you walk us through the steps necessary to parse XML file?
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DocumentBuilderFactory factory =
DocumentBuilderFactory.newInstance();
factory.setValidating(true);
DocumentBuilder domBuilder = factory.newDocumentBuilder();
Document doc = domBuilder.parse(XMLFile);
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Is
it necessary to validate XML file against a DTD?
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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.
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What
is XPath?
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XPath stands for XML Path
Language
XPath is a syntax for defining parts of an XML document
XPath is used to navigate through elements and attributes in an XML
document
XPath contains a library of standard functions
XPath is a major element in XSLT
XPath is designed to be used by both XSLT and XPointer
XPath is a W3C Standard
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What
is XSL?
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XSLT - a language for
transforming XML documents
XSLT is used to transform an XML document into another XML document, or
another type of document that is recognized by a browser, like HTML and
XHTML.
Normally XSLT does this by transforming each XML element into an
(X)HTML element.
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What
is a DTD and a Schema?
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The XML Document Type
Declaration contains or points to markup declarations that provide a
grammar for a class of documents. This grammar is known as a
document type definition or DTD.
The DTD can point to an external subset containing markup declarations,
or can contain the markup declarations directly in an internal subset,
or can
even do both.
A Schema is:
XML Schemas express shared vocabularies and allow machines to carry out
rules made by people. They provide a means for defining the structure,
content
and semantics of XML documents.
Schemas are a richer and more powerful of describing information than
what is possible with DTDs.
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