quality-driven refactoring - uni bremen filerebecca tiarks quality-driven refactoring references [1]...

Quality-Driven RefactoringRebecca Tiarks

Quality-Driven Refactoring

Rebecca Tiarks


Overview• what is quality?• what is software-quality?• quality-driven refactoring

- modelling software-qualities- deal with trade-offs

• measuring quality with metrics• software refactoring process• transformation examples


What is Quality?• “The degree to which a set of inherent

characteristics fulfills requirements”[ISO 9000:2000]

• „Qualität ist die Übereinstimmung von Ist und Soll, also die Erfüllung von Erfordernissen und Erwartungen“[Wikipedia]


Software Quality• “quality in computer software is a controversial

field. For some, software quality is a largely aesthetic and practical issue, dealing with the question of how efficiently and elegantly a computer program performs a task and source code looks (see Programming style). For others, quality is defined as strict conformance to requirements and absence of bugs.” [Wikipedia]


Software Quality• Conformance to explicitly stated functional

[correctness] and non-functional requirements [performance, security, maintainability, usability, etc.]


Quality-Driven Refactoring• achieving one or more specific non-

functional requirements (NFR)• analyze software qualities to determine

which transformations are appropriate• evaluate effect with a specific set of

metrics


Modelling Software Qualities• concept of soft-goals• relationship between quality-requirements

and design decisions• achievement is judged by the sufficiency

of contributions from other soft-goals• soft-goals can be related to other

soft-goals


Soft-Goal Interdependency Graph(SIG)

links• AND - soft-goal is fulfilled if all linked goals are

fulfilled• OR – soft-goal is fulfilled if one of the linked

goals is fulfilledcontributionspositive “help” (+) and “make” (++)negative “hurt”(-) and “brake” (--)


Soft-Goal Interdependency Graph(SIG)

Source: Software Refactoring guided by multiple soft-goals


Trade-Offs• fulfilment of one soft-goal hurts the

fulfilment of another soft-goal• conflicting soft-goals have to be

traded off• speedup porgram without sacrifing code

complexity


Quality Metricscomplexity • lines of code (LOC)• Mc Cabe's complexity

(defined on control flow graph of a program):M = e - n + 2 e = edgesn = nodes


Quality Metricstime performance• CPU cycles in relation to input• Cache misses, in relation to the input size


Software Refactoring Process1. setting up the goal-reasoning model as a SIG2. quantitatively measuring software metrics to

claim which soft-goal should be applied first3. picking an effective refactoring among various

transformations that contribute the soft-goal4. applying the selected refactoring technique

which leads to iterative evaluations back in step 2.


Transformationsloop unrolling• instructions that are called in multiple iterations of

the loop are combined into a single iteration


Transformationsloop tiling• partitions a loop’s iteration space into smaller

blocks, so as to help data in a loop stays in the cache until it is reused


Transformationsloop interchanging• the loop interchange transformation reverses the

order of two adjacent loops in a loop nest.


Transformationsarray padding and interchanging• the array padding transformation sets a dimension

in an array to a new size.


Example• simple Fortran program for matrix

multiplication

• goal: speedup 20 times without increasing complexity more than 4 times

Source: Software Refactoring guided by multiple soft-goals


Conclusion• There are several approaches to enhance

quality• difficult because quality is soft-subjective• methods to analyse and transform

developed but just in prototype version


References[1] L. Thadvildari and K. Kontogiannis. Requirements driven Software

Re-engineering framework. In WCRE 2001, pages 71-81, 2001[2] Y. Yun et al. Software refactoring guided by multiple soft –goals.

In WCRE 2003[3] B. Du Bois and T.Mentis. Describing the impact of refactoring on

internal program quality.[4] L. Thadvildari Ph.D Thesis “Quality-Driven Object-Oriented Re-

engineering Framework”, University of Waterloo, Department of Electrical and Computer Engineering, 2003.

[5] L. Tahvildari, K.Kontogiannis, "Quality-Driven Object-Oriented Code Restructuring", In Proceedings of ICSE Workshop on Software Quality, Edinburgh, Scotland, pp. 47-52, May 2004.

quality-driven refactoring - uni bremen filerebecca tiarks quality-driven refactoring references [1]...

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