Application Refactoring
with D i P tt
ith Design Patterns
Mark Tabladillo, Ph.D.
March 31, 2003

Introduction
The YTSS (Youth Tobacco Surveillance
System) started in 1998
y )
YTS = Youth Tobacco Survey
GYTS = Global Youth Tobacco Survey
Since 1998, over 1,000,000 surveys
have b
h been processed f 35 states and
d for t t d
100 international sites

Design Patterns Inherency
“Design Pattern” = Routine solution to a
reoccurring p
g problem
Observer Pattern = Model/View
Mediator Pattern = SAS/AF Frame
Singleton Pattern = Frames and SCL
standalone code
Point: Patterns are inherently inside
SAS and operating systems

How to Start with Design Patterns
Shalloway and Trott (2002), Design
p
Patterns Explained
Patterns do not stand alone, but interact
Pattern relationships improve with
refactoring (defined as the intentional
restructuring of classes)

When to Create Design Patterns
A previous project has reusable code
Current code is large
Good for long-term or complex
applications (especially to allow for
modifications)

Specific Development
Strategy
Customized nonvisual classes
First version 6 12 was used
6.12
Datasets generate code (see other
paper)
Conversion to version 8 and
consolidation
lid ti

Output Class
Changing printer orientation (landscape
vs. portrait)
p )
Changing printer font and font size
In Windows 2000 margin specification
2000,
needs to drive linesize and pagesize

Win32 Class
Put all Windows functionality in one
p
place
Accesses a table with Windows 32
errors
Calls Win32 API with SASCBTBL
Interfaces a windows Visual Basic
I t f i d Vi lB i
control

Region Class
“Region” is the base level of
y
customization for surveys
Drives the assignment of LIBNAMEs
Defines output filenames

SurveyAnalyzer
Strategy Design Pattern – have five
p g
programs to run, and the class
,
determines which one to use
Consolidation: Later refactored along
with the region class

Dataset Attribute Classes
ATTRC/ATTRN information
Open and Close Datasets
Children have:
Al
Always VARNUM
Sometimes VARLEN
Sometimes VARTYPE
S ti
Sometimes values

Final Classes
Expansion: enumerated structure
Hierarchy
SurveyYear
State
Region
AnnualCode (periodically updated)
SentenceParser (functional)

New Changes
Expansion: enumerated structure
SurveyYearAnalyzer
StateAnalyzer
RegionAnalyzer
Analyzer classes form abstract base for
processes,
processes now in their own classes
Total Classes Currently: 44

Applying Refactoring
How organized is organized??
Refactoring is choreographed
Sometimes expansion
Sometimes consolidation
Coding frameworks are increasingly
important,
important even for web work

Four Lessons
Recognize that all intentionally structured
languages have inherent design pattern
structure.
Consider adding design patterns even if it
means more code.d
Expect to continuously apply refactoring to
large or complex applications.
l l li ti
Continuously learn and apply design patterns.