1. XML in Web Technologies
Martin Kruliš
by Martin Kruliš (v1.2)

2. XML eXtensible Markup Language
Universal format for semistructured data
Plain text interleaved with XML markup
Designed for structural (tree-like) data
The structure of a document can be specified
By a grammar (schema) designed by the author of the application
Tools and libraries for XML processing
Parsing and construction (SAX, DOM)
Searching (XPath, XQuery)
Transformations
by Martin Kruliš (v1.2)

3. XML Sample
<?xml version="1.0" encoding="utf-8"?> <addressbook> <person id="1"> <name>Karel</name> <surname>Novák</surname> </person> <person id="2"> <name>Jane</name> <surname>Doe</surname> </addressbook>
Note that XML syntax is similar to HTML as they both origin from SGML. However, XML format is more strict (case sensitive, all tags must be paired, attribute values must be quoted, …).
by Martin Kruliš (v1.2)

4. XML Validation Document Structure Document Semantics
XML document is well formed if it conforms to XML specification (tag syntax)
Well formed documents can be parsed correctly
Document Semantics
XML document is valid (with respect to given schema) if its structure can be derived from the grammar specified in the schema
Validation can be performed by existing tools, which are also integrated in parsers
by Martin Kruliš (v1.2)

5. XML Validation Document Schema DTD XML Schema
Simple schema syntax embedded in XML specification
Defines only the document (elements) structure
No constraints for textual data
Could be included in XML document
XML Schema
More robust language, more features
Schema definition is also a XML document
Supported by most parsers
There are also other languages for specifying XML schema (Relax, Relax NG, Schematron, …); however, they are not widely used (at least not on the web).
Example 1
by Martin Kruliš (v1.2)

6. Parsing Simple API for XML (SAX) Document Object Model (DOM)
Processes document sequentially
Reports important events in sequential processing
Opening and closing tags, found attributes, text, …
For one-way or streaming processing
Document Object Model (DOM)
Similar API to HTML DOM
Entire object is loaded in a object tree structure
For modifications, transformations, …
by Martin Kruliš (v1.2)

7. XPath XPath Query language for XML documents
Reflects the tree-based structure of the data and operates on sets of nodes
Each query is a sequence of steps, each step takes set of nodes and produces another set
Also contains filtering predicates and basic set of functions (arithmetics, logical and string fncs, …)
/descendant::foo[attribute::id]/child::bar
Selects elements bar, which are direct children of those elements foo, which have attribute id
by Martin Kruliš (v1.2)

8. XPath Axes preceding ancestor parent following-sibling
preceding-sibling
self
following
namespace
child
attribute
descendant
descendant-or-self
by Martin Kruliš (v1.2)

9. (XML, HTML, or plain text)
Presenting XML
Extensible Stylesheet Language (XSL)
XSL = XSLT + XSL-FO (+ XPath)
XSLT – transformation language
XSL-FO – set of formatted objects
XSLT
XML document
XSLT processor
The result
(XML, HTML, or plain text)
by Martin Kruliš (v1.2)

10. Presenting XML plain text JSON data … HTML document XML document
Browser
XSL-FO document
XSLT processor
XSL formatter
PDF
XSLT šablona
XSLT template
TeX source code
TeX
by Martin Kruliš (v1.2)

11. XSLT XSL Transformations
Language that specifies transformation templates
The template is also an XML
The templates…
Use XPath to select parts of the transformed XML document
Each part is then transformed using given rules
The result of an XML transformation is either XML document, HTML document, or plain text
The language is Turing complete
Example 2
by Martin Kruliš (v1.2)

12. AJAX Asynchronous Javascript and XML
XML is used as universal format for transferring data (usually from server to client)
Can be parsed using DOM API in Javascript
Has been replaced by JSON in most cases
XML advantages over JSON
Document validation
XPath searching
XSLT transformations
by Martin Kruliš (v1.2)

13. Web Services Web Services
Set of standards for remote method invocation
Simple Object Access Protocol (SOAP)
XML based protocol for data marshaling
SOAP messages are transferred via HTTP
Web Service Description Language (WSDL)
Interface definition language that specifies the details of a web service (operations, message format, …)
Universal Description, Discovery & Integration (UDDI)
Registry for web services
Operates also as a web service
by Martin Kruliš (v1.2)

14. XML Applications XML Applications on the Web
Data exchange and application integration
Universal nature of the XML makes it perfect candidate for situations, when separate subjects need to exchange data or integrate functionality
Simple storage for tree-shaped data
If a relational database does not fit your problem
XML data can be easily visualized by XSLT
Special cases
Application configuration …
by Martin Kruliš (v1.2)

15. Discussion
by Martin Kruliš (v1.2)