Transcript The Power of Separating Data, Business Logic

The Power of Separating
Data, Business Logic and
Presentation
in Web Application Design
C. Daniel Chase
The University of Tennessee at Chattanooga
In the beginning…
way back in ’93 or so…
 Web pages were built by hand
 Contained lots of text and little graphics
 Did not change—i.e., were Static
 Updates were manual
 Initially used as a reference resource for
information that did not change (much)
Early Dynamic Pages
 It was realized that web pages did not have to
be Static
 They could be driven by Applications or
Database content
 Tools & languages were created and
optimized for this capability—for example
Perl, PHP & MySQL
 But, pages were built with the Application
Logic and Presentation and sometimes Data
embedded in ONE monolithic ‘web page’
Along Comes XML & Friends
 With the introduction of XML (eXtensible
Markup Language) data exchange formats
began to have a common format
 XSL (eXtensible Stylesheet Language) for
Structure
 XPath for selection of XML for use
 The use of XML allows you to repurpose data
into any format desired
CSS for Presentation
 Two parts of a web design
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
Content
Presentation
 Content provided by Application & Data
 Presentation or ‘Look’ controlled by CSS
Pulling it all together…
Begin with the End in Mind
 Visualize what your end goal is visually
 Break it down, what parts are :
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Presentation
Static content or Structure
Dynamic Data
 How do you need to obtain the Data?
Go Forward… One Step at a Time
1. Write Applications to deliver pure XML
output containing the Data to be presented
2. Convert the raw XML to XHTML for
browsers to display with XSLT
3. Finally, add some ‘Style’ with CSS
The UTC Search Engine
 Multiple Sources of Data
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People – LDAP Query to Novell eDirectory
Departments – MySQL Database
Experts – LDAP Query
Web Sites – MySQL Database
Web Pages – UT’s Ultraseek Search Engine
 Each Data source output in XML by
Application
The Tools
 LAMP Server
 Linux host – Red Hat Enterprise Linux AS v3
 Apache web server – version 2.0.52
 MySQL – version 3.23
 PHP – version 5.03
 PHPMyAdmin
 Easy management of MySQL databases
 Demo
 EXSLT – Enhanced XSL Template functions
 ISO 8601 into RFC 822 date format conversion
The Application – Multisearch
 PHP 5 Application
 Takes advantage of improved XML/XSLT
handling in PHP 5
 DOM XML functions
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DomDocument()
loadXML()
file_get_contents()
xsltprocessor()
importStyleSheet()
transformToXML()
The Application – Multisearch
 LDAP Functions to access eDirectory stored
information

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Example function: get_results()
Function outputs LDAP results in XML
 MySQL Functions to access databases of
Departments, Web Sites

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Example function: get_departments2()
MySQL output as XML
 XML RPC call to Ultraseek for web pages
 Example function: get_ultraseek()
 Output of request is already XML
Let’s take a closer look…
 Putting our own look to UT’s Search Engine Results
 In the beginning, there was raw XML from the Search
Engine as Data
 XML Example (local)
 Then there was the conversion to XHTML for Structure
and static content
 XSL Example (local)
 Applied to the Results (local)
 Finally the Presentation was controlled by CSS
 CSS Example (Local)
 The Final Result
 Finished page
The Results
 How does this benefit you?
 Changes in ‘design’ do not effect Application Data
handling: You can modify the Presentation or Structure
without touching the Application itself
 Changes in Data only Indirectly effect Presentation: If
you Add additional fields, they are ignored until XSL
modified to display them; You must be aware of Data
removal or restructuring
 You can rearrange the page using XSL and display the
Same DATA in different ways: Rearrange display and
turn-off unneeded graphics for a PDA, or use a smaller
portion of the data embedded in another page