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Importing Wikidata short description: "Set of software engineering methods" |
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{{Short description|Set of software engineering methods}}
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▲{{no footnotes|date=August 2012}}
In [[computer programming]], '''program slicing''' is the computation of the set of program statements, the '''program slice''', that may affect the values at some point of interest, referred to as a '''slicing criterion'''. Program slicing can be used in [[debugging]] to locate source of errors more easily. Other applications of slicing include [[software maintenance]], [[Optimization (computer science)|optimization]], [[Program analysis (computer science)|program analysis]], and [[Non-interference (security)|information flow control]].
Slicing techniques have been seeing a rapid development since the original definition by [[Mark Weiser]]. At first, slicing was only static, i.e., applied on the source code with no other information than the source code. [[Bogdan Korel]] and [[Janusz Laski]] introduced ''dynamic slicing'', which works on a specific execution of the program (for a given execution trace).<ref>{{cite journal |last1=Korel |first1=Bogdan |last2=Laski |first2=Janusz |title=Dynamic Program Slicing |journal=Information Processing Letters |date=1988 |volume=29 |issue=3 |pages=155–163 |doi=10.1016/0020-0190(88)90054-3 |citeseerx=10.1.1.158.9078 }}</ref> Other forms of slicing exist, for instance path slicing.<ref>{{Cite book|last1=Jhala|first1=Ranjit|last2=Majumdar|first2=Rupak|title=Proceedings of the 2005 ACM SIGPLAN conference on Programming language design and implementation |chapter=Path slicing |date=2005|series=PLDI '05|___location=New York, NY, USA|publisher=ACM|pages=38–47|doi=10.1145/1065010.1065016|isbn=9781595930569|s2cid=5065847 }}</ref>
== Static slicing ==
Based on the original definition of Weiser,<ref>{{Cite thesis|last=Weiser|first=Mark David|title=Program Slices: Formal, Psychological, and Practical Investigations of an Automatic Program Abstraction Method|date=1979|degree=PhD Thesis|publisher=University of Michigan|url=https://dl.acm.org/citation.cfm?id=909356|place=Ann Arbor, MI, USA}}</ref> informally, a static program slice S consists of all statements in program P that may affect the value of variable v
=== Example ===
<source lang="c">▼
For example, consider the C program below. Let's compute the slice for ( write(sum), sum ). The value of sum is directly affected by the statements "sum = sum + i + w" if N>1 and "int sum = 0" if N <= 1. So, slice( write(sum), sum) is the union of three slices and the "int sum = 0" statement which has no dependencies:
<ol>
<li>slice( sum = sum + i + w, sum),</li>
<li>slice( sum = sum + i + w, i),</li>
<li>slice( sum = sum + i + w, w), and</li>
<li>{ int sum=0 }.</li>
</ol>
It is fairly easy to see that slice( sum = sum + i + w, sum) consists of "sum = sum + i + w" and "int sum = 0" because those are the only two prior statements that can affect the value of sum at "sum = sum + i + w". Similarly, slice( sum = sum + i + w, i) only contains "for(i = 1; i < N; ++i) {" and slice( sum = sum + i + w, w) only contains the statement "int w = 7".
When we union all of those statements, we do not have executable code, so to make the slice an executable slice we merely add the end brace for the for loop and the declaration of i. The resulting static executable slice is shown below the original code below.
int i;
int sum = 0;
int product = 1;
int w = 7;
for(i = 1; i < N; ++i) {
sum = sum + i + w;
product = product * i;
}
write(sum);
write(product);
</syntaxhighlight>
<
int i;
int sum = 0;
int w = 7;
for(i = 1; i < N; ++i) {
sum = sum + i + w;
}
write(sum);
</syntaxhighlight>
In fact, most static slicing techniques, including Weiser's own technique, will also remove the <code>write(sum)</code> statement. Since, at the statement <code>write(sum)</code>, the value of <code>sum</code> is not dependent on the statement itself. Often a slice for a particular statement x will include more than one variable. If V is a set of variables in a statement x, then the slice for (x, V) is the union of all slices with criteria (x, v) where v is a variable in the set V.
== Lightweight forward static slicing approach ==
A very fast and scalable, yet slightly less accurate, slicing approach is extremely useful for a number of reasons. Developers will have a very low cost and practical means to estimate the impact of a change within minutes versus days. This is very important for planning the implementation of new features and understanding how a change is related to other parts of the system. It will also provide an inexpensive test to determine if a full, more expensive, analysis of the system is warranted. A fast slicing approach will open up new avenues of research in metrics and the mining of histories based on slicing. That is, slicing can now be conducted on very large systems and on entire version histories in very practical time frames. This opens the door to a number of experiments and empirical investigations previously too costly to undertake.<ref>{{Cite journal|last1=Alomari|first1=Hakam W.|last2=Collard|first2=Michael L.|last3=Maletic|first3=Jonathan I.|last4=Alhindawi|first4=Nouh|last5=Meqdadi|first5=Omar|date=2014-05-19|title=srcSlice: very efficient and scalable forward static slicing|journal=Journal of Software: Evolution and Process|language=en|volume=26|issue=11|pages=931–961|doi=10.1002/smr.1651|issn=2047-7473|citeseerx=10.1.1.641.8891|s2cid=18520643 }}</ref>
== Dynamic slicing ==
An example to clarify the difference between static and dynamic slicing. Consider a small piece of a program unit, in which there is an iteration block containing an if-else block. There are a few statements in both the <code>if</code> and <code>else</code> blocks that have an effect on a variable. In the case of static slicing, since the whole program unit is looked at irrespective of a particular execution of the program, the affected statements in both blocks would be included in the slice. But, in the case of dynamic slicing we consider a particular execution of the program, wherein the <code>if</code> block gets executed and the affected statements in the <code>else</code> block do not get executed. So, that is why in this particular execution case, the dynamic slice would contain only the statements in the <code>if</code> block.
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* [[Data dependency]]
* [[Frama-C]] a tool which implements slicing algorithms on [[C program]]s.
* [[Partial dead code elimination]]
== Notes ==
{{reflist}}
== References ==
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* Jens Krinke. "Program Slicing", In Handbook of Software Engineering and Knowledge Engineering, Volume 3: Recent Advances. [[World Scientific Publishing]], 2005
* Silva, Josep. "A vocabulary of program slicing-based techniques", ACM Computing Surveys, Volume 44, Issue 3, [[Association for Computing Machinery]], June 2012
*[http://www.users.miamioh.edu/alomarhw/ Alomari HW] et al. "srcSlice: very efficient and scalable forward static slicing". [https://onlinelibrary.wiley.com/journal/20477481 Wiley Journal of Software: Evolution and Process] ('''JSEP'''), DOI: 10.1002/smr.1651, Vol. 26, No. 11, pp. 931-961, 2014.
==External links==
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* [http://indus.projects.cis.ksu.edu/index.shtml Indus Project] (part of Bandera checker)
* [http://www.cs.wisc.edu/wpis/html/ Wisconsin Program-Slicing Project]
{{Program analysis}}
[[Category:Debugging]]
[[Category:Program analysis]]
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