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XML

The Extensible Markup Language (XML) is a W3C-recommended general-purpose markup language for creating special-purpose markup languages, capable of describing many different kinds of data. In other words XML is a way of describing data and an XML file can contain the data too, as in a database. It is a simplified subset of Standard Generalized Markup Language (SGML). Its primary purpose is to facilitate the sharing of data across different systems, particularly systems connected via the Internet. Languages based on XML (for example, Geography Markup Language (GML), RDF/XML, RSS, Atom, MathML, XHTML, SVG,Klip and MusicXML) are defined in a formal way, allowing programs to modify and validate documents in these languages without prior knowledge of their particular form.

Features of XML

1. XML provides a text-based means to describe and apply a tree-based structure to information. At its base level, all information manifests as text, interspersed with markup that indicates the information’s separation into a hierarchy of character data, container-like elements, and attributes of those elements.

2. The fundamental unit in XML is the character, as defined by the Universal Character Set. Characters are combined in certain allowable serial combinations to form an XML document. The document consists of one or more entities, each of which is typically some portion of the document’s characters, encoded as a series of bits and stored in a text file.

3. XML files may be served with a variety of Media types. RFC3023 defines the types “application/xml” and “text/xml”, which say only that the data is in XML, and nothing about its semantics.

4. XML makes no prohibitions on how it is used. Although XML is fundamentally text-based, software quickly emerged to abstract it into other, richer formats, largely through the use of datatype-oriented schemas and object-oriented programming paradigms

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Top 10 Interview Questions When Hiring XML Developers

As XML becomes more pervasive, hiring managers won’t have to look very hard to find candidates claiming to have experience working on projects involving XML. Despite this trend, it is still not an easy task to find a truly skilled XML developer. This fact, combined with the increasing compensation awarded to job candidates, makes hiring the right people one of the most important parts of any IT project. Consequently, the list of questions below is intended to be a guide for managers faced with the task of filling positions within their organizations that require a solid understanding of the foundations of XML-related technologies.

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.

Differences Between XML and HTML
Table 1.

XML

HTML

User definable tags

Defined set of tags designed for web display

Content driven

Format driven

End tags required for well formed documents

End tags not required

Quotes required around attributes values

Quotes not required

Slash required in empty tags

Slash not required

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.

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 SAX.

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.

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.

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>

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 the candidate know the somewhat obscure answer.

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.

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.

Comments»

1. vvvvv - July 10, 2006

hi

2. amjad - September 15, 2006

XML – Learn

3. amjad - September 15, 2006

learning

4. Amit Singh,Pune - December 25, 2006

Diff Between SAX and DOM parsers

5. lipu - February 16, 2007

give some new questions………..

6. k.venkatachalam - March 9, 2007

give notes on XML related.
Diff Between erroe and Exception.

7. Reshmi - December 10, 2010

1.difference between XML and HTML is misleading
Ans: Please find the actual difference between HTML and XML. in the below post

http://dotnettution.blogspot.com/2010/12/difference-between-xml-and-html.html


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