TECHNOLOGIES FOR WEB APPLICATIONS

May 16 • Notes • 2192 Views • 5 Comments on TECHNOLOGIES FOR WEB APPLICATIONS

TECHNOLOGIES FOR WEB APPLICATIONS :

INTRODUCTION TO XML :

XML stands for extensible markup language. It is the only one markup language , which is used by good organizations and companies . Previously in history , it was the GML ( Generalized markup language ) , whose use and  implementation  cost was so high and time taking that it was really difficult for the organizations using it . Later  this GML became ISO certified and renamed to SGML ( Standard Generalized Markup Language ) . But still the implementation expense was so high. So later a new markup language was developed to meet the requirements as :

• Page Designing
• sharing the data
• storing the data
• exchanging the data
• It is the mother of other markup languages
• It is used in case of deployment descriptor

XML documents contains a root element . This element is the parent of all other elements and these elements in an XML document forms a document tree . The tree starts at the root and branches to the lowest level of the tree . All elements here have sub elements or child elements and

The syntax that represents this is :

<root>

<child>

<subchild>……….</subchild>

</child>

</root>

DIFFERENCE BETWEEN XML AND HTML :

 HTML  :

In HTML we can use the fixed or predefined tags . All the tags in HTML need not be closed . All tags are case insensitive and it does not give any compilation error . To create and get the designs we use only one .html file . Inside the HTML , we can embed XML file and HTML files can not be easily parsed by java programs . HTML I used to format and display the data .

XML  :

 In XML we can use user defined tags and all the tags must be necessarily closed . All tags are case sensitive and it can give compilation error . To get the design we have to use minimum number of files.XML files can be parsed by java program and we can embed HTML inside XML . XML is used to transport the data .

DISPLAYING XML USING CSS :

 To format an XML document , We can use CSS . An example of how to use a CSS style sheet to format an XML document is :

Catalog.xml

<?xml version=”1.0” encoding=”ISO-8859-1”?>
<?xml-stylesheet type=”text/css” ?>
<College>
<Student>
<name>Lorem Ipsum</name>
<company>OurEducation</company>
<phoneNo>011111111</phoneNo>
</student>
</student>
<name>Rout</name>
<company>ABC01</company>
<phoneNo>011111111</phoneNo>
</student>
</college>

design.class

college
{
Background-color:#ffffff;
Width: 100%;
}
Student
{
Display:block;
Margin-bottom:30pt;
Margin-left: 0;
}
name
{
Color: #FF0000;
Font-size: 20pt;
}
phoneNo
{
Display:block;
Color: #000000;
Margin-left: 20pt;
}

OUTPUT :

Lorem Ipsum OurEducation

011111111

Rout ABC01

011111111

COVERTING XML TO HTML FOR DISPLAY  :

There are many ways to convert XML to HTML for display like :

1>    By using extensible stylesheet language . Using XSL is the best way to convert XML to HTML for display because it has many advantages like this language is very compact and so even very complicated HTML can be displayed using small programs . It is also easy to reuse the XML for other purposes and as it is non procedural language , we will have to mention only what we want to accomplish and hence it decreases the use of recursive function .

2>    By using HTML alone . If the XML file is in simple table form and is only upto two levels deep then we can display XML using HTML only .

3>    XML can also be converted to HTML for display by using HTML with CSS . This is better than using only HTML alone. But the major disadvantage of this is that it is deficient of power and is not flexible enough  .

4>    Using HTML with JavaScript. As JavaScript is a fully general purpose programming language any possible transformation and display can take place easily . The disadvantage is that it requires very complex recursive functions which are very difficult to understand.

EMBEDDING XML INTO HTML DOCUMENT :

It is very difficult for HTML documents to support XML data processing  . Hence it is necessary to allow embedding of an XML object within an HTML document . The HTML document will then be able to support various functions depending on XML markup .

There are two purposes why XML “ islands” are permitted within an HTML document.

1>    To increase the content that is delivered to the web and to support further enhancements in XML based models .

2>    The content developers depends on HTML abilities while experimenting with XML.

Hence the result of this will be:

<html>

<body>

<xml>

</xml>

</body>

</html>

RELATIONSHIP BETWEEN HTML , XML AND SGML :

 XML , HTML and SGML are all markup languages . A markup language is a set of words and highlighted texts to define a web document . There exists a family bond between SGML , HTML and XML , that helps in developing websites .

SGML :  

It stands for Standard Generalized Markup Language . It acts as a parent in family of  languages . SGML states what other languages can do or cannot do and what changes must be brought in its tags and what the structure of the language should be . SGML passes on structures and formatting rules to markup languages .

HTML :

HTML stands for hypertext markup language . HTML is an application of SGML  nd is used to design pages for internet browsers , create page sections and create images . We can also add functions through HTML to websites .

XML :

XML is both related to HTML and SGML. It acts as a cousin to HTML and as a nephew to SGML . XML can be defined as a subset of SGML. It belongs to the family of markup languages and is similar to HTML except that it has different functions . XML inherits properties from SGML but is created to make its own family .

WAYS TO USE XML DATA FILES AND DTD :

A DTD or a Document Type Definition is required for proper use of XML, because a DTD contains the rules of all XML documents and the language is always defined by the DD . For proper  use of XML we require  :

•  Elements , having syntax <!ELEMENT along with the name of the element and then the description. Like for example <!ELEMENT Bisakha(#PCDATA)>
• It requires Data . The description in above example (#PCDATA) represents parsed character data . We can also mention (#CDATA) or character data , that cannot be parsed or shown .
• The Elemts described above also contains some sub elements . For example  <!ELEMENT machine (brand, type)>

<!ELEMENT name(#PCDATA)>

<!ELEMENT department(#PCDATA)>

Hence  the Element machine has two subtypes i:e name and department .

• Empty elements also needed . Its syntax is  <!ELEMENT separator EMPTY>
• DTD cab be external and such DTD can be written as <!DOCTYPE  root-element name SYSTEM”address”>
• A DTD can also act as XML document also  . For internal DTD we must write <!DOCTYPE root element name and [followed by its defination]> after writing <?xml version=”1.0”?>

 VALIDATION OF A XML DOCUMENT  :

For XML validation to take place the XML file must be downloaded , a file which contains an XSD      file and stored in server host . This must be copied into a webpage . For validation of XML file we must  :

• Copy the file into the given text area
• The XSD file must also be copied to the clipboard and then click on the present validate button .
• When asked for XSD file , copy the XSD file that is present in your clipboard to the text area and click on the button .
•   The error messages will start changing once you begin editing files . The links at the bottom of the page must be clicked  when editing files as it highly helps in error correcting and downloading files that are error free.

ADAPTING RE METHODS TO WEB APPLICATION AND REQUIREMENT ENGINEERING ACTIVITIES  :

There  are various methods available for all activities in RE. one-size-fits-all  must be avoided in order to succeed . these methods must be used to point out or specify web engineering and time of specific projects . There are various requirement types like Functional requirement , content requirement , quality requirement , system environment requirement , user interface requirements , evolution requirements and project constraints . Requirement engineering activities is used for discovering each customers keen interests and wants .It gives a good and powerful platform to optimize subjects and offers. It provides increased engagement of customers , developed loyalty and good promotional campaign etc.

REWRITING HTML AS XML :

XML and HTML are two different concepts of markup language. We cannot rewrite HTML as XML perfectly . It is because XML  is a generalized form of HTML but still its not precise and clear. We use HTML to display data and XML to transfer data.

ADAPTING RE METHODS TO WEB APPLICATIONDIFFERENCE BETWEEN XML AND HTMLREQUIREMENT ENGINEERING ACTIVITIESTECHNOLOGIES FOR WEB APPLICATIONSXML

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