Thursday, November 5, 2009

XML Interview Questions

What are the different kind of parsers used in XML?
There are 2 parsers:
1) DOM (Document object model): This will interpret Complete XML document.Microsoft major concentration is DOM Parser.
2) SAX Parser (Simple Aplication programming Interface for XML): This will interpret XML document based on the event occurrence only it wont interpret complete document at a time. Sun mycrosystems major concentration is SAX Parser.What is XPath?
XPath is used to navigate through elements and attributes in an XML document.

Difference between XML and HTML
What is the differnece between XML and HTML
1) XML is not a replacement for HTML.
2) XML and HTML were designed with different goals.
3) XML was designed to describe data and to focus on what data is.
4) HTML was designed to display data and to focus on how data looks.
5) HTML is about displaying information, XML is about describing information
User definable tags
Content driven
End tags required for well formed documents
Quotes required around attributes values
Slash required in empty tags
Defined set of tags designed for web display
Format driven
End tags not required
Quotes not required
Slash not required

What is XML and Binary Serialization?
XML Serialization serializes the object into an xml file. This file is human readable and can be shared with other applications.

Binary serialization is more efficient but the serialized file is in binary format. It may not make any sense for a human being to open this file and understand what it contains. It is a stream of bytes.

What is XSL?
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.
XPath - a language for navigating in XML documents
XSL-FO - a language for formatting XML documents
What is DTD and Schema in XML

A DTD is:

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.

In summary, schemas are a richer and more powerful of describing information than what is possible with DTDs.
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 it’s written in SGML, the international standard meta language for
text document markup (ISO 8879).
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.
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
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.
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.
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;
and Robin Cover’s SGML Web pages are at
For a little light relief, try Joe English’s ‘Not the SGML
FAQ’ at

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.
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
HTML is just one of many SGML or XML applications—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++.
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.
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.
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
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.
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.
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
* 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).
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.

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.

Wednesday, November 4, 2009

Web Services Interview Questions

1) What is a Web service?
Many people and companies have debated the exact definition of Web services. At a minimum, however, a Web service is any piece of software that makes itself available over the Internet and uses a standardized XML messaging system.
XML is used to encode all communications to a Web service. For example, a client invokes a Web service by sending an XML message, then waits for a corresponding XML response. Because all communication is in XML, Web services are not tied to any one operating system or programming language--Java can talk with Perl; Windows applications can talk with Unix applications.
Beyond this basic definition, a Web service may also have two additional (and desirable) properties:
First, a Web service can have a public interface, defined in a common XML grammar. The interface describes all the methods available to clients and specifies the signature for each method. Currently, interface definition is accomplished via the Web Service Description Language (WSDL). (See FAQ number 7.)
Second, if you create a Web service, there should be some relatively simple mechanism for you to publish this fact. Likewise, there should be some simple mechanism for interested parties to locate the service and locate its public interface. The most prominent directory of Web services is currently available via UDDI, or Universal Description, Discovery, and Integration. (See FAQ number 8.)
Web services currently run a wide gamut from news syndication and stock-market data to weather reports and package-tracking systems. For a quick look at the range of Web services currently available, check out the XMethods directory of Web services.
2) What is new about Web services?
People have been using Remote Procedure Calls (RPC) for some time now, and they long ago discovered how to send such calls over HTTP.
So, what is really new about Web services? The answer is XML.
XML lies at the core of Web services, and provides a common language for describing Remote Procedure Calls, Web services, and Web service directories.
Prior to XML, one could share data among different applications, but XML makes this so much easier to do. In the same vein, one can share services and code without Web services, but XML makes it easier to do these as well.
By standardizing on XML, different applications can more easily talk to one another, and this makes software a whole lot more interesting.
3) I keep reading about Web services, but I have never actually seen one. Can you show me a real Web service in action?
If you want a more intuitive feel for Web services, try out the IBM Web Services Browser, available on the IBM Alphaworks site. The browser provides a series of Web services demonstrations. Behind the scenes, it ties together SOAP, WSDL, and UDDI to provide a simple plug-and-play interface for finding and invoking Web services. For example, you can find a stock-quote service, a traffic-report service, and a weather service. Each service is independent, and you can stack services like building blocks. You can, therefore, create a single page that displays multiple services--where the end result looks like a stripped-down version of or my.excite.
4) What is the Web service protocol stack?

The Web service protocol stack is an evolving set of protocols used to define, discover, and implement Web services. The core protocol stack consists of four layers:
Service Transport: This layer is responsible for transporting messages between applications. Currently, this includes HTTP, SMTP, FTP, and newer protocols, such as Blocks Extensible Exchange Protocol (BEEP).
XML Messaging: This layer is responsible for encoding messages in a common XML format so that messages can be understood at either end. Currently, this includes XML-RPC and SOAP.
Service Description: This layer is responsible for describing the public interface to a specific Web service. Currently, service description is handled via the WSDL.
Service Discovery: This layer is responsible for centralizing services into a common registry, and providing easy publish/find functionality. Currently, service discovery is handled via the UDDI.
Beyond the essentials of XML-RPC, SOAP, WSDL, and UDDI, the Web service protocol stack includes a whole zoo of newer, evolving protocols. These include WSFL (Web Services Flow Language), SOAP-DSIG (SOAP Security Extensions: Digital Signature), and USML (UDDI Search Markup Language). For an overview of these protocols, check out Pavel Kulchenko's article, Web Services Acronyms, Demystified, on
Fortunately, you do not need to understand the full protocol stack to get started with Web services. Assuming you already know the basics of HTTP, it is best to start at the XML Messaging layer and work your way up.
5) What is XML-RPC?
XML-RPC is a protocol that uses XML messages to perform Remote Procedure Calls. Requests are encoded in XML and sent via HTTP POST; XML responses are embedded in the body of the HTTP response.
More succinctly, XML-RPC = HTTP + XML + Remote Procedure Calls.
Because XML-RPC is platform independent, diverse applications can communicate with one another. For example, a Java client can speak XML-RPC to a Perl server.
To get a quick sense of XML-RPC, here is a sample XML-RPC request to a weather service (with the HTTP Headers omitted):



The request consists of a simple element, which specifies the method name (getWeather) and any method parameters (zip code).

Here is a sample XML-RPC response from the weather service:


The response consists of a single element, which specifies the return value (the current temperature). In this case, the return value is specified as an integer.
In many ways, XML-RPC is much simpler than SOAP, and therefore represents the easiest way to get started with Web services.
The official XML-RPC specification is available at Dozens of XML-RPC implementations are available in Perl, Python, Java, and Ruby. See the XML-RPC home page for a complete list of implementations.
6) What is SOAP?
SOAP is an XML-based protocol for exchanging information between computers. Although SOAP can be used in a variety of messaging systems and can be delivered via a variety of transport protocols, the main focus of SOAP is Remote Procedure Calls (RPC) transported via HTTP. Like XML-RPC, SOAP is platform independent, and therefore enables diverse applications to communicate with one another.

To get a quick sense of SOAP, here is a sample SOAP request to a weather service (with the HTTP Headers omitted):



As you can see, the request is slightly more complicated than XML-RPC and makes use of both XML namespaces and XML Schemas. Much like XML-RPC, however, the body of the request specifies both a method name (getWeather), and a list of parameters (zipcode).

Here is a sample SOAP response from the weather service:



The response indicates a single integer return value (the current temperature).
The World Wide Web Consortium (W3C) is in the process of creating a SOAP standard. The latest working draft is designated as SOAP 1.2, and the specification is now broken into two parts. Part 1 describes the SOAP messaging framework and envelope specification. Part 2 describes the SOAP encoding rules, the SOAP-RPC convention, and HTTP binding details.
7) What is WSDL?

The Web Services Description Language (WSDL) currently represents the service description layer within the Web service protocol stack.
In a nutshell, WSDL is an XML grammar for specifying a public interface for a Web service. This public interface can include the following:

Information on all publicly available functions.
Data type information for all XML messages.
Binding information about the specific transport protocol to be used.
Address information for locating the specified service.

WSDL is not necessarily tied to a specific XML messaging system, but it does include built-in extensions for describing SOAP services.

Below is a sample WSDL file. This file describes the public interface for the weather service used in the SOAP example above. Obviously, there are many details to understanding the example. For now, just consider two points.
First, the elements specify the individual XML messages that are transferred between computers. In this case, we have a getWeatherRequest and a getWeatherResponse. Second, the element specifies that the service is available via SOAP and is available at a specific URL.





WSDL File for Weather Service


Using WSDL, a client can locate a Web service, and invoke any of the publicly available functions. With WSDL-aware tools, this process can be entirely automated, enabling applications to easily integrate new services with little or no manual code. For example, check out the GLUE platform from the Mind Electric.
WSDL has been submitted to the W3C, but it currently has no official status within the W3C. See this W3C page for the latest draft.
8) What is UDDI?
UDDI (Universal Description, Discovery, and Integration) currently represents the discovery layer within the Web services protocol stack.
UDDI was originally created by Microsoft, IBM, and Ariba, and represents a technical specification for publishing and finding businesses and Web services.
At its core, UDDI consists of two parts.
First, UDDI is a technical specification for building a distributed directory of businesses and Web services. Data is stored within a specific XML format, and the UDDI specification includes API details for searching existing data and publishing new data.
Second, the UDDI Business Registry is a fully operational implementation of the UDDI specification. Launched in May 2001 by Microsoft and IBM, the UDDI registry now enables anyone to search existing UDDI data. It also enables any company to register themselves and their services.
The data captured within UDDI is divided into three main categories:
White Pages: This includes general information about a specific company. For example, business name, business description, and address.
Yellow Pages: This includes general classification data for either the company or the service offered. For example, this data may include industry, product, or geographic codes based on standard taxonomies.
Green Pages: This includes technical information about a Web service. Generally, this includes a pointer to an external specification, and an address for invoking the Web service.
You can view the Microsoft UDDI site, or the IBM UDDI site. The complete UDDI specification is available at
Beta versions of UDDI Version 2 are available at:
Hewlett Packard
9) How do I get started with Web Services?
The easiest way to get started with Web services is to learn XML-RPC. Check out the XML-RPC specification or read my book, Web Services Essentials. O'Reilly has also recently released a book on Programming Web Services with XML-RPC by Simon St.Laurent, Joe Johnston, and Edd Dumbill.
Once you have learned the basics of XML-RPC, move onto SOAP, WSDL, and UDDI. These topics are also covered in Web Services Essentials. For a comprehensive treatment of SOAP, check out O'Reilly's Programming Web Services with SOAP, by Doug Tidwell, James Snell, and Pavel Kulchenko.
10) Does the W3C support any Web service standards?
The World Wide Web Consortium (W3C) is actively pursuing standardization of Web service protocols. In September 2000, the W3C established an XML Protocol Activity. The goal of the group is to establish a formal standard for SOAP. A draft version of SOAP 1.2 is currently under review, and progressing through the official W3C recommendation process.
On January 25, 2002, the W3C also announced the formation of a Web Service Activity. This new activity will include the current SOAP work as well as two new groups. The first new group is the Web Services Description Working Group, which will take up work on WSDL. The second new group is the Web Services Architecture Working Group, which will attempt to create a cohesive framework for Web service protocols.

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