An Analysis of the Current Program Slicing and Algorithmic Debugging Based Techniques

slice provides additional information: it says for each statement in the slice if the condition c =‘\n’ will be satisfied or not. (1) read(text); [false] (2) read(n); [false] (3) lines = 1; [c!=‘\n’] (4) chars = 1; [false] (5) subtext = ""; [false] (6) c = getChar(text); [false] (7) while (c != ‘\eof’) [false] (8) if (c == ‘\n’) [false] (9) then lines = lines + 1; [false] (10) chars = chars + 1; [false] (11) else chars = chars + 1; [false] (12) if (n != 0) [false] (13) then subtext = subtext ++ c; [false] (14) n = n 1; [false] (15) c = getChar(text); [false] (16) write(lines); [c!=‘\n’] (17) write(chars); [false] (18) write(subtext); [false] Fig. 23. Abstract slice of Figure 1 (a) with respect to 〈16, c =‘\n’, [(1), text = “hello world!\eof”]〉 Question answered: Under which variable values do the program’s statements affect or are affected by the slicing criterion? Main applications: Program comprehension. 2.24 Amorphous Slicing (Harman and Danicic, 1997) All approaches to slicing discussed so far have been based on two assumptions: the slice preserves (part of) the semantics of the program, and it is “syntax preserving”, i.e., the slice is a subset of the original program statements. In contrast, amorphous slices [Harman and Danicic 1997] preserve the semantics restriction but they drop the syntactic restriction: amorphous slices are constructed using some program transformation which simplifies the program and which preserves the semantics of the program with respect to the slicing criterion. In the literature (see, e.g. [Ward 2002; 2003; Ward and Zedan 2007], when a slicing technique is restricted to statement deletion it is also referred to as syntactic slicing, as opposed to semantic slicing where only the semantic restriction must be preserved. The syntactic freedom allows amorphous slicing to perform greater simplifications, thus often being considerably smaller than conventional program slicing. These simplifications are very convenient in the context of program comprehension where the user needs to simplify the program as much as possible in order to understand a part of the semantics of the program having the syntax less importance. For instance, consider Program 1 in Figure 24 together with the slicing criterion 〈3, {chars}〉. An intraprocedural static slice of this program would contain the whole program (Program 1). In contrast, an interprocedural static slice would remove statements 4, 5 and 6 (Program 2). Finally, its amorphous slice would be