top 10 Giant list of XML interview questions and answers
1. What is XML?
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 meta languageâ€â€a language for describing
other languagesâ€â€which lets you design your own markup languages
for limitless different types of documents. XML can do this because
it’s written in SGML, the international standard meta language for
text document markup (ISO 8879).
2. What is a markup language?
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 (eg 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 not normally
re-usable for anything else.
3. Where should I use XML?
Its goal is to enable generic SGML to be served, received, and
processed on the Web in the way that is now possible with HTML.
XML has been designed for ease of implementation and for interoperability
with both SGML and HTML.
Despite early attempts, browsers never allowed other SGML, only
HTML (although there were plugins), and they allowed it (even encouraged
it) to be corrupted or broken, which held development back for over
a decade by making it impossible to program for it reliably. XML
fixes that by making it compulsory to stick to the rules, and by
making the rules much simpler than SGML.
But XML is not just for Web pages: in fact it’s very rarely used
for Web pages on its own because browsers still don’t provide reliable
support for formatting and transforming it. Common uses for XML
include:
Information identification because you can define your own markup,
you can define meaningful names for all your information items.
Information storage because XML is portable and non-proprietary,
it can be used to store textual information across any platform.
Because it is backed by an international standard, it will remain
accessible and processable as a data format. Information structure
XML can therefore be used to store and identify any kind of (hierarchical)
information structure, especially for long, deep, or complex document
sets or data sources, making it ideal for an information-management
back-end to serving the Web. This is its most common Web application,
with a transformation system to serve it as HTML until such time
as browsers are able to handle XML consistently. Publishing the
original goal of XML as defined in the quotation at the start of
this section. Combining the three previous topics (identity, storage,
structure) means it is possible to get all the benefits of robust
document management and control (with XML) and publish to the Web
(as HTML) as well as to paper (as PDF) and to other formats (eg
Braille, Audio, etc) from a single source document by using the
appropriate stylesheets. Messaging and data transfer XML is also
very heavily used for enclosing or encapsulating information in
order to pass it between different computing systems which would
otherwise be unable to communicate. By providing a lingua franca
for data identity and structure, it provides a common envelope for
inter-process communication (messaging). Web services Building on
all of these, as well as its use in browsers, machine-processable
data can be exchanged between consenting systems, where before it
was only comprehensible by humans (HTML). Weather services, e-commerce
sites, blog newsfeeds, AJaX sites, and thousands of other data-exchange
services use XML for data management and transmission, and the web
browser for display and interaction.
4. Why is XML such an important development?
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 off the Web; and it removes the more complex options of SGML,
making it easier to program for.
5. Describe the differences between XML and HTML.
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.
XML
User definable tags
Content driven
End tags required for well formed documents
Quotes required around attributes values
Slash required in empty tags
HTML
Defined set of tags designed for web display
Format driven
End tags not required
Quotes not required
Slash not required
6. Describe the role that XSL can play when dynamically
generating HTML pages from a relational database.
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.
7. What is SGML?
SGML is the Standard Generalized Markup Language (ISO 8879:1986),
the international standard for defining descriptions of the structure
of different types of electronic document. There is an SGML FAQ
from David Megginson at http://math.albany.edu:8800/hm/sgml/cts-faq.htmlFAQ;
and Robin Cover’s SGML Web pages are at http://www.oasis-open.org/cover/general.html.
For a little light relief, try Joe English’s ‘Not the SGML
FAQ’ at http://www.flightlab.com/~joe/sgml/faq-not.txtFAQ.
SGML is very large, powerful, and complex. It has been in heavy
industrial and commercial use for nearly two decades, and there
is a significant body of expertise and software to go with it.
XML is a lightweight cut-down version of SGML which keeps enough
of its functionality to make it useful but removes all the optional
features which made SGML too complex to program for in a Web environment.
8. Aren’t XML, SGML, and HTML all the same thing?
Not quite; SGML is the mother tongue, and has been used for describing
thousands of different document types in many fields of human activity,
from transcriptions of ancient Irish manuscripts to the technical
documentation for stealth bombers, and from patients’ clinical records
to musical notation. SGML is very large and complex, however, and
probably overkill for most common office desktop applications.
XML is an abbreviated version of SGML, to make it easier to use
over the Web, easier for you to define your own document types,
and easier for programmers to write programs to handle them. It
omits all the complex and less-used options of SGML in return for
the benefits of being easier to write applications for, easier to
understand, and more suited to delivery and interoperability over
the Web. But it is still SGML, and XML files may still be processed
in the same way as any other SGML file (see the question on XML
software).
HTML is just one of many SGML or XML applicationsâ€â€the one
most frequently used on the Web.
Technical readers may find it more useful to think of XML as being
SGML– rather than HTML++.
9. Who is responsible for XML?
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 W3C as a Recommendation on Feb
10, 1998.
10. Why is XML such an important development?
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 data both
on and off the Web; and it removes the more complex options of SGML,
making it easier to program for.
top 11-20 Giant list of XML interview questions and answers
continue:top 10 Giant list of XML interview questions and answers
11. Give a few examples of types of applications that can
benefit from using XML.
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.
12. What is DOM and how does it relate to XML?
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.
13. What is SOAP and how does it relate to XML?
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.
14. 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.
15. 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 standardized 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 style sheet 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).
16. 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.
17. 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.
18. 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>
19. 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.
20. 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 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.
Changes in ajax 4.0 Preview 5
Declarative Attribute Changes
It is no longer necessary to include a sys:activate attribute on the body of a page containing declarative markup.
The attributes used in declarative markup have been modified slightly to minimize the number of namespaces used, and to minimize cross browser issues with some html attributes.
1. All attributes that contain an expression (e.g. {{ .. }}) or markup extension (e.g. {binding ..}) must now be prefixed with “sys:”. For example, previously you could do this:
<input type=”text” value=”{{ foo }}” />
You must now do this:
<input type=”text” sys:value=”{{ foo }}” />
Some attributes such as ‘src’ of an image already required this due to various browser issues or side effects. It was confusing when you needed sys and when you didn’t. Also, “top level bindings” naturally require sys as otherwise the expression/binding would be seen as actual content and possibly rendered to the user.
2. The ‘code’ attributes have been moved into ‘sys’.
code:if -> sys:if
code:before -> sys:codebefore
code:after -> sys:codeafter
3. The ‘class’ attributes have been moved into ‘sys’.
class:foo -> sys:class-foo
4. The ‘style’ attributes have been moved into ‘sys’.
style:font-size=”8” -> sys:style-font-size=”8”
Top Level Bindings
Support for "top level" expressions and bindings. Previously these were only supported within the context of a template marked with sys-template. For example, to bind the value of an input to a javascript object, you might do this:
<input type="text" sys:value="{binding bar,source={{foo}} }" />
This binds the value to the ‘bar’ field of a global ‘foo’ object. You can use other bindings to update the value, or directly with Sys.Observer:
Sys.Observer.setValue(foo, “bar”, “newValue”);
Binding the content of an element as text or HTML
You may bind to the content of a node using the new sys:innertext and sys:innerhtml attributes. Choose the appropriate attribute depending on whether or not you want to allow HTML in the value to be interpreted as HTML. For example, if you have a variable named ‘foo’ set to the value “<p>hello</p>”:
<div sys:innertext=”{{ foo }}”></div>
Will result in seeing <p>hello</p> in the browser.
<div sys:innerhtml=”{{ foo }}”></div>
Will result in the <p> tag being interpret as a paragraph tag.
The difference is in how the value is inserted. “sys:innertext” injects a text node with the given value. “sys:innerhtml” sets the innerHTML of the target element. Note that while “innerText” is an Internet Explorer only concept, “sys:innertext” is not an Internet Explorer only attribute. The name is semantically correct, despite it being implemented differently than IE’s native innerText field.
Template Changes
The pseudo variables accessible within template markup have been improved. Previously there was no way to get to the current context, only the parent context ($parentContext). Also, there was no simple way of getting to the current set of data being rendered.
The $parentContext pseudo variable is no longer. Now there is simply the $context variable. From there you can get to all the information available on the Sys.UI.TemplateContext class:
$context.parentContext
$context.data
$context.dataItem
$context.index
… and others. You also still have access to these for convenience:
$dataItem ß the current dataItem (e.g. $context.dataItem)
$index ß index of the current dataItem (e.g. $context.dataIndex)
$element ß The last element to either begin or close
$component ß The last component that was created
The Sys.UI.Template.instantiateIn() method has been changed to accept the data as well as the dataItem for the context that is created.
Before: template.instantiateIn(container, dataItem, dataIndex, insertBeforeNode, parentContext)
Now: template.instantiateIn(container, data, dataItem, dataIndex, insertBeforeNode, parentContext)
DataView Improvements
DataView now has the following events:
rendering
itemRendering
itemRendered
rendered
DataView Dynamic Templates and Placeholders
From each event you have the opportunity to override the parameters the DataView uses to render. The itemTemplate and itemPlaceholder can both be changed dynamically from the rendering and itemRendering events. This allows you to dynamically determine both the default template and placeholder used for all items, without having to change the corresponding DataView properties, as well as dynamically determine them for each individual item. This enables some interesting scenarios where the template used to render each item can be determined based on the data. It also means each item can be rendered into a different location. For example, you might have a Stock Ticker DataView that renders negative stocks with a negativeItemTemplate and positive ones with a positiveItemTemplate. Or you might have a product listing DataView where items of different categories are rendered into separate placeholders, possibly in very distant parts of the page.
Binding Converters and Expandos
Bindings now support the concept of named converters that are set onto the Sys.Binding.converters field. There are none out of the box, but you may now define your own and refer to them by name. For example:
{binding foo,convert=myconverter}
This would look for a converter defined like so:
Sys.Binding.converters.myconverter = function(valueToConvert, binding) {
// convert
}
In addition, you may now set expandos onto the binding object and refer to them from your converter. This allows you to semantically describe what you want in a binding in any custom way you require for any specific binding. It allows you to parameterize a converter function. For example, this example sets a ‘format’ expando on the binding object despite that not being a field or property the binding natively has:
{binding foo,convert=format,format=MM/dd}
Sys.Binding.converters.format = function(value, binding) {
// binding.format === MM/dd
}
UpdatePanel Support
Preview 4 was not compatible with UpdatePanel in ASP.NET 3.5 due to changes to the data format UpdatePanel renders, and the inline script it renders in ASP.NET 4.0. The 4.0 scripts are now designed to work with either 3.5 or 4.0 on the server. To support UpdatePanel with these scripts, you must replace the partial rendering script (MicrosoftAjaxWebForms.js) with the 4.0 version. If you do not use an update panel, you must disable partial rendering.
No UpdatePanel:
<asp:ScriptManager runat=”server” EnablePartialRendering=”false”>
<Scripts>
<asp:ScriptReference Name=”MicrosoftAjax.js” Path=”~/scripts/MicrosoftAjax.js” />
</Scripts>
</asp:ScriptManager>
With UpdatePanel:
<asp:ScriptManager runat=”server”>
<Scripts>
<asp:ScriptReference Name=”MicrosoftAjax.js” Path=”~/scripts/MicrosoftAjax.js” />
<asp:ScriptReference Name=”MicrosoftAjaxWebForms.js” Path=”~/scripts/MicrosoftAjaxWebForms.js” />
</Scripts>
</asp:ScriptManager>
Html Encoded Code Expressions in asp.net 4.0
Html Encoded Code Expressions
Some ASP.NET sites (especially with ASP.NET MVC) rely heavily on using <%= expression %> (often called “code nuggets”) to write some text to the response. When you use code nuggets, it is easy to forget to HTML-encode the text. When the text comes from user input, it can leave pages open to an XSS (Cross Site Scripting) attack.
ASP.NET 4 introduces the following new syntax for code expressions:
<%: expression %>
This syntax uses HTML encoding by default when writing to the response. This new expression effectively translates to the following:
<%= HttpUtility.HtmlEncode(expression) %>
For example, <%: Request["UserInput"] %> would html encode the value of Request["UserInput"].
The goal of this feature is to make it possible to replace all instances of the old syntax with the new syntax so that you are not forced to decide at every step which one to use. However, there are cases in which the text being output is meant to be HTML or is already encoded, in which case this could lead to double encoding.
For those cases, ASP.NET 4 introduces a new interface, IHtmlString, along with a concrete implementation, HtmlString. Instances of these types let you indicate that the return value is already properly encoded (or otherwise examined) for displaying as HTML, and that therefore the value should not be HTML-encoded again. For example, the following should not be (and is not) HTML encoded:
<%: new HtmlString("<strong>HTML that is not encoded</strong>") %>
ASP.NET MVC 2 helper methods have been updated to work with this new syntax so that they are not double encoded, but only when you are running ASP.NET 4. This new syntax does not work when you run an application using ASP.NET 3.5 SP1.
Keep in mind that this does not guarantee protection from XSS attacks. For example, HTML that uses attribute values that are not in quotation marks can contain user input that is still susceptible. Note that the output of ASP.NET controls and ASP.NET MVC helpers always includes attribute values in quotation marks, which is the recommended approach.
Likewise, this syntax does not perform JavaScript encoding, such as when you create a JavaScript string based on user input.
Posted in: asp.net | Tags: asp.net 4.0 html html encoed code expression httputility userinput ihtmlstring