1 Overview of XSL

2 Outline We will use Roger Costello’s tutorial The purpose of this presentation is  To give a quick overview of XSL  To describe what is available in Costello’s tutorial

3 Introduction and Motivation

4 Web Services A Web service is written using servlets, JSP or a similar technology The Web service interacts with databases using JDBC The Web service interacts with clients using a Web server The Web service may interact with other applications

5 The Traditional Approach The Web service generates HTML pages in order to interact with clients Changing the HTML pages necessitates a change in the Java code Different clients (e.g., pc, palm-pilot, cell phone) may require different HTML pages  Different versions of the Java code should be maintained HTML is not suitable for information exchange, e.g., interacting with automated agents (knowbots)

6 The XML Approach: Separating Content from Style The Web service generates XML documents Automated agents get XML documents in response to requests Other clients get HTML pages that are generated by adding style to the XML documents  It is easy to implement different styles for different clients

7 Where Should the Business Rules be Implemented? An example of a business rule  All products are now on sale at a discount of 10% Business rules may change frequently Where should they be implemented?  Database application  Servlet or JSP  XML transformation (by means of XSLT)

8 XML Transformations CSS can add style to XML, but it cannot transform an XML document  How can you change the price of a product in an XML document describing that product?  How can you add (to the XML document) the information that the product is on sale? XSLT can do just that

9 Even Just Adding Style May Require a Transformation Consider an XML document that describes several products and their prices How can you create a table with two columns – one for products and and one for prices? Cannot be done in CSS, but can be done in XSL

10 Different Types of Transformations Transform an XML document into  An HTML page  Another XML document  A text file Roger Costello’s tutorial covers the three types (and more)

11 How to Transform? Write an XSL style sheet Use an XSL processor to transform the XML document according the XSL style sheet, or Add a Stylesheet PI (Processing Instruction) to the XML document and display the XML document using a browser (recent versions only, e.g., IE 6 or Netscape 7)

12 Roger Costello’s Tutorial It describes the XSL language It gives many examples  There are actual files of the examples  Each example is in a separate folder and it includes An XML document An XSL style sheet The result of the transformation as produced by an XSL processor

13 A Few Things About XSL XSL is a high-level, functional language The syntax is a bit peculiar and possibly confusing An XSL style sheet is a valid XML document  Valid with respect to the XSL namespace Therefore, commands in XSL are XSL elements

14 How to Use the Examples Since XSL is a high-level language, XSL style sheets are relatively short and easy to understand It is easy to modify an existing style sheet into another style sheet with a similar functionality  The many examples of Costello are very useful as a starting point for writing your own style sheets

15 The Main Elements of XSL  This element is for extracting values from the given XML document  This element is for looping,, etc.  This element is for conditional processing

16 Examples of Xpath Expressions /university/department/course  This Xpath expression matches any path that starts at the root, which is a university element, passes through a department element and ends in a course  This Xpath expression matches any path that starts at the current element, continues to a child which is a department element and ends at a course element with a year attribute that is equal to 2002

17 How to Write a Style Sheet for Transforming XML to HTML Write a template in XHTML Add some necessary elements and PI (Processing Instructions) Inside the XHTML template, use XSL elements in order to extract values from the given XML document