XML document is a collection of data. In other words it doesn’t make much difference between the other files that store data. A XML in a database format is a self describing, portable, and can describe data in tree or graph structure. XML is a sort of Database Management System (DBMS).
XML provides storage, schemas, query languages, programming interfaces and so on .It lacks in triggers, queries, multi-user access that a real database constitutes. The main advantage of XML is that the data is portable and it allows you to have nested entries.
XML allows you to preserve physical document structure, supports document level transactions and execute queries in an XML query language.
Mapping the XML document schema to the database schema does the transfer of data between XML documents and a database. Mappings between document schemas and database schemas are performed on attributes and text. There are 2 mappings that are generally used to map on XML document schema to the database schema:
I) TABLE BASED MAPPING
ii) OBJECT RELATIONAL MAPPING
Native XML databases are designed especially to store XML documents .It is always possible to store data in XML documents in a native XML database. This is done so, when your data is semi-structured. Although, this kind of data can be stored in object oriented and hierarchical databases, it is always better to store it in a native XML database. It enables us to retrieve data much faster than a relational database. One more reason is to store data in a native XML database is to exploit XML specification capabilities, such as executing XML queries.
The need for manipulating XML on the server increases as the need for XML increases.XML and ASP are a very efficient and a powerful combination.XML is a simple and a powerful tool for web developers.XML was created to handle complex Web documents. XML allows you to define all your own tags with rules such as data description and data relationships. XML is used in order to remove the cumbersome problems that were faced with HTML. Information can be accessed easier using XML. ASP and XML are powerful tools for creating dynamic web pages.
ASP uses XML as a tool in its application for a simple reason that data in HTML is allowed to transmit between dissimilar platforms, whereas XML allows us to express complex structure. Moreover it allows us to create our own tags with all sorts of rules. A new document instance can be created using MSXML.There are a number of ways to access XML data from an ASP page. Document Object Model (DOM) plays an important role in retrieving the XML data from ASP. In DOM a document is viewed as a tree of nodes. Every node of the tree can be accessed randomly. The main advantage is that it provides all functions in an Object based way.An XML parser based on DOM from Microsoft is MSXML.This component is used for accessing the XML documents.
There are two groups of DOM programming interfaces.The first group defines interfaces required for writing the application. The second group defines interfaces that are required to assist developers. Once the DOM Object is created on the server, your own XML document can be created. The XML document can be easily parsed on the server in an ASP and then the results can be sent to the client.
An XML Schema defines the elements, child elements and the attributes that can appear in a document. It can also define the order, the number of child elements, the data types for elements and attributes. In DBMS, Schema is a description of a database structure. Internal structures such as tables and fields can be defined using schemas. Schema defines tables and fields that make up the data. Schemas are defined using constraints.
There are two types of constraints:
1. CONTENT CONSTRAINTS
2. DATATYPE CONSTRAINTS
An XML schema is a set of schema components in which there are 13 kinds of grouped components under 3 categories primary, secondary and helper components.
The primary components include
* SIMPLE TYPE DEFINITIONS
* COMPLEX TYPE DEFINITIONS
* ATTRIBUTE TYPE DEFINITIONS
*? ELEMENT DECLARATIONS
An XML schema consists of components such as type definitions and element declarations. They are used to access the validity of the well-formed element and attribute information items.
The purpose of XML schema structures schema describes a class of XML documents by using schemas components. Schemas provide specifications and additional information such as normalization and element values. Thus, XML schemas can be used to describe and catalogue XML documents. The XML schema validators allow us to check whether the instance of an document meets the requirements. The XML data can be described and validated using the XSD (XML Schema Editor). XSD is written in XML, so it doesn’t require a parser.
XML schemas are successors of the DTD’s. XML schemas are extensible, richer and more useful than DTD’s. XML schemas can support data types and name spaces. The difference between the schemas and DTD’s are:
|
DIFFERENCES |
DTD'S |
SCHEMAS |
| LANGUAGE |
DTD's are written using EBNF (Extended Backus-Naur Form) |
Schemas are written using XML. |
| DATA CONSTRAINTS |
DTD's have minimal data constraints. |
Schemas allow more specific constraints |
| USER DEFINED TYPES |
DTD's limit to a fixed set of content models |
Schemas provide greater flexibility and expressing content. |
XML tools allows the developers to produce XML in a wide variety of situations such as comparing two documents, validating the XML documents, to check whether a file is well formed, etc., There are a lot of tools available, including those tools for creating and editing XML or building e-commerce applications.
few of the tools are listed below:
• Microsoft XML Diff and Patch
It is a set of tools that will allow you to compare two XML documents. It detects addition, deletion and detects the changes between two XML documents. It ignores order attributes, insignificant white spaces, and it doesn’t care about document coding. These tools if used on a structured data leads to suboptimal results, since they don’t have the capacity of recognizing the tree based structure.
• XSD schema validator
This allows the validation of XML documents against an W3C XML schema or XML data reduced schema. It checks whether the given document is well formed and has a valid schema model.
• Microsoft XSD interference 1.0
Allows you to create an XML schema definition language if a well formed XML file is available, then it generates an XSD that can validate that XML file.
• XML CONTENT TOOLS
The XML content tools allow us to create edit and publish XML.The XML content tools were originally designed for publishing needs. XML pro from vervet logic is another relatively cheap and worth XML editing tool. The user interface helps you to make quick work.
• XmetaL
XMetaL from SoftQuad is another affordable tool designed to make quick work of creating and editing files. It is a set of tools designed to simplify the implementation of XML applications. Two companies offer XML application tool kits. It enables you to deliver the contents in a short time to multiple channels, reduces complexity and cost of content. It supports DOM that includes extensive documentation. It also supports COM.
• Breeze Commerce Studio
Bluestone software offers Breeze Commerce studio for creation of XML and Java based applications. It imports schema from XML DTD’s, XML documents and JDBC/ODBC databases.
It allows us to add data types and constraints to the elements of the schema.
• Standalone and Single User content tools
Standalone, singleuser XML content tools are very cheap, since they require the least amount of development time and effort. If you have to handle XML creating, editing and publishing for print, web, investigate the product lines of Abortext and interleaf. RAD XML persistent tools are used for easy process, display and share complex data across applications with minimum coding.
• Altova STYLEVISION 2004
Altova STYLEVISION 2004 is a new XML tool for web developers that provide extensive utilities for migrations. It is a visual editing tool that allows us to create style sheets and forms easily based on XML schemas or databases. It is a powerful database editing tool that allows you to generate reports directly from databases to XML.
• Altova XML SPY2004
Altova XML SPY2004 Enterprise Edition is one of the most important XML tools for advanced application development. These tools have been used extensively for editing and working with XML technologies. It uses the Enhanced Grid View to manage elements or attribute creation.
• XT
XT is a more powerful tool, which is easy to use .The understanding of the tree structure is made easy using XT, since the file you want to turn into a result tree is the name of the last parameter.
XT is easy to use if you are familiar with Java.
Simple Object Access Protocol (SOAP) is a protocol that can be used for accessing the Web pages. SOAP or Simple Object Access Protocol is an XML based Object invocation Protocol. SOAP was developed for distributed applications to communicate through HTTP and firewalls. SOAP is platform independent and it uses XML and HTTP to access services, servers and objects.
SOAP consists of 3 parts:
* SOAP ENVELOPE: Defines a framework for expressing what is in a message and who should handle it. The SOAP envelope namespace defines header and body element names and the encoding style.
* SOAP ENCODING RULES: Defines a mechanism for exchanging instances of application defined data types. An encoding rule means an encoding style to know how it is applied to a specific data.
* SOAP RPC: Defines a method to represent Remote Procedure Calls and responses. Soap RPC uses a request/response model for message exchanges. The request that is sent to the end point is the call and the response it sends represents the result of the call sent.
SOAP has the following features:
* PROTOCOL independence
* LANGUAGE independence
* PLATFORM AND OS independence
SOAP is a way by which programs communicate with other programs using XML.SOAP uses XML to encapsulate data that needs to be sent to a remote subroutine. In more simple terms SOAP is a way by which Java objects and COM objects communicate with each other. A SOAP client is a program that creates an XML document that contains information required to invoke a method remotely in a distributed system.
A SOAP server is a code that listens to the SOAP messages and acts as a distributor and an interpreter. SOAP defines encoding rules called Base level codings. The encodings can be either
* SIMPLE ENCODINGS
* COMPOUND ENCODINGS
SIMPLE ENCODINGS are simple types like ints, floats, strings or user defined data types. These include data types such as arrays of bytes and Enumerations.
COMPOUND ENCODINGS include data types such as arrays and structures.
XML is a means of exchanging data between applications. It allows the developers to describe and structure their data in their own formats. As the XML gave more emphasis on data rather than formatting, the data in the XML document can be formatted in two ways:
* USING CSS
* USING XSL
Cascade Style Sheet( CSS)
Initially, Cascading Style sheets (CSS) were used for formatting the data in the XML documents. It allows the Web Developers to define a formatting for the elements in XML and the same can be applied to as many documents you like. The advantages are:
* It has a Precise control over presentation
* It is Resolution Independent
* It downloads Faster
* It is easy to maintain
Though it has a lot of advantages it also has following disadvantages.
* The order of elements for display cannot be changed
* An element cannot be processed more than once.
* Generated text cannot be added to the presentation
USING eXtesible Stylesheet Language (XSL):
The difficulties that were encountered with CSS were removed by making use of XSL. XSL is an application of XML It allows you to create high performance XML based systems by integrating Server side XML processing’s. The need for transforming data from one format to the other results in splitting XSL into two groups:
i) XSLT – It describes how to transform XML. Document into other formats.
ii) XSL-FO- It describes formatting details of each element in the XML document.
i) XSLT:
The XML Style sheet Language Transformation (XSLT) is a mechanism of transforming one form of XML documents to the other form. It is a set of templates based on Xpath expressions that tells how to fetch a particular node from the XML documents. It is a part of XSL, which is a style sheet language for XML. XSLT is widely used in Websites Content Management to convert XML into HTML pages. It uses Xpath to define parts that match one or more templates. Xpath is an query language that allows you to identify the nodes. It can select nodes in any direction. An XSLT processor is used to perform transformations of XML document in to other formats based on the given XSLT document.
ii) XSL_FO:
XSL-FO means Extensible Formatting Objects. There are two different ways in which the XML document can be formatted. They are:
* Layout Based formatting and
* Content Based formatting
In a layout based formatting, the limitations of the target may constrain the content or appearance on the page, whereas in a Content Based Formatting, the target medium is generated to accommodate the information being formatted. The XSL FO allows you to make formatting and styling options to your document.