1.What is XML?
- Extensible Markup Language (XML) is the universal language for data on the Web
- XML is a technology which allows us to create our own markup language.
- XML documents are universally accepted as a standard way of representing information in platform and language independent manner.
- XML is universal standard for information interchange.
2.What are the benefits of XML?
There are many benefits of using XML on the Web :
- Simplicity- Information coded in XML is easy to read and understand, plus it can be processed easily by computers.
- Openness- XML is a W3C standard, endorsed by software industry market leaders.
- Extensibility - There is no fixed set of tags. New tags can be created as they are needed.
- Self-description- In traditional databases, data records require schemas set up by the database administrator. XML documents can be stored without such definitions, because they contain meta data in the form of tags and attributes.
- Contains machine-readable context information- Tags, attributes and element structure provide context information that can be used to interpret the meaning of content, opening up new possibilities for highly efficient search engines, intelligent data mining, agents, etc.
- Separates content from presentation- XML tags describe meaning not presentation. The motto of HTML is: "I know how it looks", whereas the motto of XML is: "I know what it means, and you tell me how it should look." The look and feel of an XML document can be controlled by XSL style sheets, allowing the look of a document to be changed without touching the content of the document. Multiple views or presentations of the same content are easily rendered.
- Supports multilingual documents and Unicode-This is important for the internationalization of applications.
- Facilitates the comparison and aggregation of data - The tree structure of XML documents allows documents to be compared and aggregated efficiently element by element.
- Can embed multiple data types - XML documents can contain any possible data type - from multimedia data (image, sound, video) to active components (Java applets, ActiveX).
- Can embed existing data - Mapping existing data structures like file systems or relational databases to XML is simple. XML supports multiple data formats and can cover all existing data structures and .
- Provides a 'one-server view' for distributed data - XML documents can consist of nested elements that are distributed over multiple remote servers. XML is currently the most sophisticated format for distributed data - the World Wide Web can be seen as one huge XML database.
3.What is a well-formed XML document?
If a document is syntactically correct it can be called as well-formed XML documents. A well-formed document conforms to XML's basic rules of syntax:
- Every open tag must be closed.
- The open tag must exactly match the closing tag: XML is case-sensitive.
- All elements must be embedded within a single root element.
- Child tags must be closed before parent tags.
- A well-formed document has correct XML tag syntax, but the elements might be invalid for the specified document type.
4.What is a valid XML document?
If a document is structurally correct then it can be called as valid XML documents. A valid document conforms to the predefined rules of a specific type of document:
- These rules can be written by the author of the XML document or by someone else.
- The rules determine the type of data that each part of a document can contain.
- 5.What is a Processing Instruction in XML?
6.How does the XML structure is defined?
XML document will have a structure which has to be defined before we can create the documents and work with them. The structural rules can be defined using many available technologies, but the following are popular way of doing so-
- Document Type Definition (DTD)
- Schema
7.What is DTD?
A Document Type Definition (DTD) defines the legal building blocks of an XML document. It defines rules for a specific type of document, including:
- Names of elements, and how and where they can be used
- The order of elements
- Proper nesting and containment of elements
- Element attributes
To apply a DTD to an XML document, you can:
- Include the DTD's element definitions within the XML document itself.
- Provide the DTD as a separate file, whose name you reference in the XML document.
8.What is XML Schema?
An XML Schema describes the structure of an XML instance document by defining what each element must or may contain.XML Schema is expressed in the form of a separate XML file.
- XML Schema provides much more control on element and attribute datatypes.
- Some datatypes are predefined and new ones can be created.
- XML Schema provides much more control on element and attribute datatypes.
9.What is a Complex Element?
A complex element is an XML element that contains other elements and/or attributes.
There are four kinds of complex elements:
There are four kinds of complex elements:
- empty elements
- elements that contain only other elements
- elements that contain only text
- elements that contain both other elements and text
10.What is a Simple Element?
A simple element is an XML element that can contain only text.
- A simple element cannot have attributes
- A simple element cannot contain other elements
- A simple element cannot be empty
- However, the text can be of many different types, and may have various restrictions applied to it
14.What are namespaces? Why are they important?
A simple element is an XML element that can contain only text.
- Namespaces are a simple and straightforward way to distinguish names used in XML documents, no matter where they come from.
- XML namespaces are used for providing uniquely named elements and attributes in an XML instance
- They allow developers to qualify uniquely the element names and relationships and make these names recognizable, to avoid name collisions on elements that have the same name but are defined in different vocabularies.
- They allow tags from multiple namespaces to be mixed, which is essential if data is coming from multiple sources.
15.What are the ways to use namespaces?
There are two ways to use namespaces:
- Declare a default namespace
- Associate a prefix with a namespace, then use the prefix in the XML to refer to the namespace.
16.What is the relevance of ElementFormDefault attribute in the Schema?
ElementFormDefault indicates whether or not locally declared elements must be qualified by the target namespace in an instance document. ElementFormDefault attribute in the Schema has the following relevance:
- Qualified: Each and every element of the Schema must be qualified with the namespace in the instance document.
- Unqualified: means only globally declared elements must be qualified with there namespace and not the local elements.
17.What is XML parser?
An XML parser is a piece of software which can do following:
- Check for well-formedness
- Validate the document
- Allows us to read, create or modify existing XML documents
Note: Parser is piece of software provided by vendors. An XML parser is built in Java runtime from JDK 1.4 onwards
18.What is DOM?
The Document Object Model (DOM) is a platform and language-independent standard object model for representing XML and related formats. DOM is standard API which is not specific to any programming language. DOM represents an XML document as a tree model. The tree model makes the XML document hierarchal by nature. Each and every construct of the XML document is represented as a node in the tree.
19.What is SAX?
SAX-Simple API for XML processing. SAX provides a mechanism for reading data from an XML document. It is a popular alternative to the Document Object Model (DOM).SAX provides an event based processing approach unlike DOM which is tree based.
20.What are the interfaces of SAX?
The interfaces of SAX are:
What is a CDATA section in XML?
- CDATA Sections are used to escape blocks of text containing characters which would otherwise be recognized as markup. All tags and entity references are ignored by an XML processor that treats them just like any character data. CDATA blocks have been provided as a convenience measure when you want to include large blocks of special characters as character data, but you do not want to have to use entity references all the time.
22.What is XSL?
eXtensible Stylesheet Language(XSL) deals with most displaying the contents of XML documents.XSL consists of three parts:
- XSLT - a language for transforming XML documents
- XPath - a language for navigating in XML documents
- XSL-FO - a language for formatting XML documents.
23.What is the role of XSL transformer?
An XSL transformer will transform in the following way:
- The source tree is obtained by parsing in a normal XML style
- The transformation is now applied to the source with the help of information available in Stylesheet.
- 24.What is XSL template?Template specifies transformation rules. A Stylesheet document can be made up of at least one template, which acts as an entry point. Every template uniquely identifies a particular node in the source tree.
25.What is XPath?XPath is an expression language used for addressing parts of an XML document. XPath is used to navigate through elements and attributes in an XML document.
29.What is XSL-FO?XSL-FO deals with formatting XML data. This can be used for generating output in a particular format like XML to PDF, XML to DOC, etc.
