R R R Program Families CSE870 Discussion April 14, 2003

R R R Family of Programs Grouping/finding COMMON functionality Reuse of designs/code across family members “Pushing design decisions as late as possible”

R R R 3 Approaches Classical Sequential : –Develop specific program completely –Subsequent programs are derived from original program –Identify specific points to be changed –Complete design process BEFORE making changes for other family members

R R R Stepwise Refinement Top-down approach –Start with abstract designs –Refine each point until you reach concrete functionality Partial design Intermediate points can have deviations –Intermediate points may not be implemented Programming for change –Keep intermediate nodes flexible Pattern Usage: Strategy, Template Tree Shape: Long and skinny

R R R Stepwise Refinement Advantages: –No extra cost: no extra specifications –Because you reverse design decisions, you can still reuse all of the ancestors prior to that intermediate point –Clean development cycle: Top-down advantages: narrowing the implementation space; no synthesis problem Disadvantages –Early decisions: have to make many design decisions early in the process –Changes to the ancestor tree can have major impact on more of the final designs –Narrow family: variation among family members may be quite small

R R R Module Specification Basic idea: Decompose functionality into modules Module: –Collection of functions to perform specific service –interface (group together collection of operations/data into one entity) Approach: –Bottom clustering of functionality into modules –Intermediate stage is a module specification Can be realized by “body implementations” for specification Module specification is not part of final program code for any family member Tree Shape: –Broader: delay design decisions until very late in process

R R R Module Specification Advantages: –More choices early (I.e., delay design decisions) –Gain independence among module implementations Parallel development –Information Hiding (via specifications) –Exploits OO properties (modularity, encapsulation, reuse, abstraction, etc.) –Documentation (via specifications) –Intermediate node: comprise multiple module specifications, thus allowing for choice among the modules for final functionality.

R R R Module Specification Disadvantages: –Cost: of developing specifications Overhead in initial specification – each functionality must be specified (well- understood) –More difficult: abstract the services/data across many possible designs/implementation –Requires “master” programmer experience

R R R When to use Module specification: –Use to specify services and abstract data types without commitments to design Use stepwise refinement for the parts that you have a clear understanding of a majority of the design

R R R Applications of Program Families Operating Systems : different versions Web browsers: across vendors and within vendor Wysiwig vs command-line editors Product-line engineering –Domain analysis/engineering

R R R Frameworks: Customize frameworks to achieve program families Module Specification: Whitebox: –Delaying design decisions until late, designer implement as appropriate Stepwise Refinement: Graybox: –Design structure is already known –At intermediate node, you can branch to a different decision, but you don’t need to backtrack to previous design decisions.