B2B Integration : A Practical Guide to Collaborative E-commerce

Extensible Markup Language (XML) 175
• Effective use of Internet — XML effectively uses the Internet to
transfer the messages securely; whereas most of the EDI message
flow occurs through expensive VANs.
6.5. XSL — Extensible Stylesheet Language
In order to display XML documents, it is necessary to have a mechanism
to describe how the document should be displayed. One of the commonly
used presentation technologies is Cascading Style Sheets (CSS) used by
HTML, but XSL (Extensible Stylesheet Language), the preferred style
sheet language of XML, is far more sophisticated than CSS. XSL is a
language that can transform XML into multiple formats, a language that
can filter, format and sort XML data and a language that uses XML as
its syntax. Currently, XSL is used primarily to transform XML semantics
into a display format like HTML that can be viewed through Web
browsers. However, XSL provides a wide variety of presentation layers
for a single XML document.
An XSL style sheet contains instructions as to how to pull out
information from the XML document and transform it into another
format, such as HTML or PDF file. The transformation of XML into
other formats is done in a declarative way rather than the conventional
scripting way, which makes it much easier to understand and maintain.
The browsers and devices such as PDAs (Personal Digital Assistants)
and cell phones each have a unique display format. A single XML
document can be presented on all these different presentation devices
by using XSL. An XSL processor, either on the client or server, can
transform XML data into the appropriate format, thereby completely
decoupling the business layer with the presentation layer. This separation
is the key to building any flexible and extensible application.
An XSL processor can have output in multiple formats taking XML
and style sheets (DTDs, schemas) as the inputs (see Figure 6.3).
XSL consists of the following three parts:
• XML Vocabulary — It describes the formatting objects portion of
XSL. The process of formatting is performed by the formatter. The
formatter may simply be a rendering engine inside a browser.
Formatting objects can be inserted into a result tree created by