Learning XML

This document Contains Contents. 

XML is not a programming language. It is a markup language; but it is successfully used by many programmers. There have been markup languages before, but in the developer community XML  is far and away the most successful.

There are number of indivisuals who have helped me with the content of this book. specially, I thank Shri Vivek Banzal (DGM) for enormous support durig writing this book.

The term Markup is a concatenation of words mark up. This refers to the traditional
way of marking up a document in the print and design worlds.

XML is a tool used to generate markup languages in general rather than a specific
markup language. Thus, rather than pre-defining a set of tags, XML defines a methodology
for tag creation. Once defined, tags are mixed with plain text in order to form an
“XML document”.

The physical structure of an XML document is composed of all the content used in that
document. The storage units, called Entities, can be part of the document or external to the
document. Each entity is identified by a unique name and contains its own contents, from
a single character inside the document to a large file that exists outside the document.

A namespace is a collection of names that is identified by a Uniform Resource Identifier
(URI). Namespaces is a methodology for creating universally unique names in an XML
document by identifying element names with a unique external resource.

To understand the need for XML, at least as it applies to the Web, you have to first
consider the role of HTML. In the early days of the Internet, some European physicists
created HTML by simplifying another markup language known as SGML (Standard
Generalized Markup Language). SGML was overly complicated, at least for the purpose of
sharing scientific documents on the Internet. So, pioneering physicists created a simplified
version of SGML called HTML that could be used to create what we now know as web pages.
The creation of HTML represented the birth of the World Wide Web a layer of visual
documents that resides on the global network known as the Internet.

CSS documents allow you to define a style for any HTML element. Thus, you can define
the style for an h1 element to be red with a font size of 6. This style can then be applied
to every h1 element on your Web site. CSS documents allow you to create a uniform style
throughout your Web documents without having to enter specific information for each h1
element in each page. If you need to change the style for an h1 element, you need to change
it only in the CSS document. If you need to override the style defined in the CSS document
for one or more of your h1 elements in a specific page, you can do this, too.

Generically, we can refer to schema as metadata, or data about data. Some of the
schema efforts are not just concerned with defining a vocabulary; they go beyond this
attempting to explain the relationships between certain types of data.
Schemas refine DTDs by permitting more precision in expressing some concepts in the
vocabulary. Schemas use a wholly different syntax than DTDs. They permit us to borrow
vocabulary from other schemas, thereby solving validation problem. Overall, schemas are
better answers to the problem of specifying vocabularies.

XSL stands for EXtensible Stylesheet Language. It started with XSL and ended up with
XSLT, XPath, and XSL-FO. The World Wide Web Consortium (W3C) started to develop XSL
because there was a need for an XML-based Stylesheet Language. XML does not use
predefined tags (we can use any tag-names we like), and therefore the meaning of each tag
is not well understood.

The eXtensible Stylesheet Language is divided into two sub-languages, eXtensible
Stylesheet Language Transformations (XSLT) and eXtensible Stylesheet Language-
Formatting Objects (XSL-FO). In this lesson, we will be looking at the basics of XSLT, which
is used to transform XML documents.

SOAP is a protocol for accessing a Web Service. SOAP is a simple XML-based protocol
to let applications exchange information over HTTP.
SOAP acts as a medium to provide basic messaging framework. On these basic messaging
frameworks abstract layers are built. It transfers messages across the board in different
protocols; it also acts as a medium to transmit XML based messages over the network.

DOM is an Application Programming Interface (API) that represents an XML file as a
document object, which allows application programs to manage the information contained in
the document object through the interface.

XML 1.0 allows you to encode your information in textual form and it allows you to
create tags which allow you to structure the information stored in XML documents. This
information must at some point be read by some program to do something useful, like
viewing, modifying or printing it.

XML 1.0 allows you to encode your information in textual form and it allows you to
create tags which allow you to structure the information stored in XML documents. This
information must at some point be read by some program to do something useful, like
viewing, modifying or printing it.

XQuery for XML is like SQL for database. XQuery is the language for querying XML
data only. The best way to explain XQuery is to say that XQuery is to XML what SQL
is to database table. XQuery is designed to query XML data — not just XML files, but
anything that can appear as XML, including database. XQuery is supported by all the major
database engines (Oracle, IBM, Microsoft, etc.). XQuery is built on with the use of XPath
expressions. XQuery is a language for finding and extracting the elements and attributes
from XML documents.

XForms is the next generation of HTML forms. XForms uses XML to create input forms
on the Web.XForms is the next generation of HTML forms. It is richer and more flexible
than HTML forms. XForms will be the forms standard in XHTML 2.0.XForms is platform
and device independent. It separates data and logic from presentation. XForms uses XML
to define form data. It stores and transports data in XML documents. It contains features
like calculations and validations of forms. XForms reduces or eliminates the need for scripting.

XSL-FO is about formatting XML data for output. It is a language for formatting XML
data. XSL-FO stands for Extensible Stylesheet Language Formatting Objects. It is based on
XML.XSL-FO is now formally named XSL.XSL-FO describes the formatting of XML data for
output to screen, paper or other media. XSL-FO is Formally Named XSL.

This chapter gives a high-level overview of how to use XML with databases. It describes
how the differences between data-centric and document-centric documents affect their usage
with databases, how XML is commonly used with relational databases, and what native XML
databases are and when to use them.

Web Services, in the general meaning of the term, are services offered via the Web. In
a typical Web services scenario, a business application sends a request to a service at a given
URL using the SOAP protocol over HTTP. The service receives the request, processes it,
and returns a response. As example of this consider a stock quote service, in which the
request asks for the current price of a specified stock, and the response gives the stock price.
This is one of the simplest forms of a Web service in that the request is filled almost
immediately, with the request and response being parts of the same method call.