W. F. Tichy, "The string-to-string correction problem with block moves," ACM Transactions on Computer Systems, vol. 2, no. 4, pp. 309--321, 1984.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....correction problem, it is implicitly assumed that the data common to and 336 appear in the same order in the two files. Furthermore, the string to string correction approach does not account for substrings in 522 appearing in several times. To resolve these limitations, Tichy [44] defined the string to string correction problem with block moves. A block move is a triple such that 32 587 717 . It represents a nonempty common substring of 969 and which is of length . Given , the file ....

....mentioned earlier is just a special case of a covering set of block moves. The minimality condition then ensures the superiority of the block moves approach to the longest common subsequence approach. The question the arises how does one construct an optimal given 341 and Tichy [44] also showed that a greedy algorithm results in a minimal cover set and that an based on a minimal cover set of block moves can be constructed in linear space and time using suffix trees. Unfortunately, the multiplicative constant in the space complexity makes the approach impractical. A more ....

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W. Tichy. The string-to-string correction problem with block moves. ACM Transactions on Computer Systems, 2(4):309-321, November 1984.

....widely used way to perform delta compression, but it does not provide good compression on files that are only slightly similar. vdelta, on the other hand, is a relatively new technique that integrates both data compression and data differencing. It is a refinement of Tichy s block move algorithm [24] that generalizes the well known Lempel Ziv technique [27] to delta compression. In our work, we use the zdelta compressor, which was shown to achieve good compression and running time in [26] The issue of appropriate distance measures between files and strings has been studied extensively, and ....

W. Tichy. The string-to-string correction problem with block moves. ACM Transactions on Computer Systems, 2(4):309--321, November 1984.

....widely used way to perform delta compression, but it does not provide good compression on files that are only slightly similar. vdelta, on the other hand, is a relatively new technique that integrates both data compression and data differencing. It is a refinement of Tichy s block move algorithm [24] that generalizes the well known Lempel Ziv technique [27] to delta compression. In our work, we use the zdelta compressor, which was shown to achieve good compression and running time in [26] The issue of appropriate distance measures between files and strings has been studied extensively, and ....

W. Tichy. The string-to-string correction problem with block moves. ACM Transactions on Computer Systems, 2(4):309--321, November 1984.

....each proxy maintains a cache mirroring the contents of its partner proxy. When the two proxies wish to send messages to each other, they should take maximum advantage of the data their partner is known to have. For clarity, this task is di erent from the standard di task. In the standard task [8], the algorithm must compute the di erences between a new source le and an old reference le. Where there is redundancy between the two les, the algorithm outputs a pointer to the repeated byte sequence in the reference le. This scenario is depicted in Figure 3 1. 33 B C D A C B D ....

Walter F. Tichy. The string-to-string correction problem with block moves. ACM Transactions on Computer Systems, 2(4):309-321, November 1984.

....fails to encode minimum sized delta files, as it does not examine data at a fine granularity and finds only matching data that are aligned at the beginning of a new line. The problem of representing the changes between versions of data was formalized as stringto string correction with block move [24] detecting maximally matching regions of a file at an arbitrarily fine granularity without alignment. However, delta compression continued to rely on the alignment of data, as in database records [23] and the grouping of data into block or line granularity, as in source code control systems ....

....between versions. Efforts to generalize delta compression to un aligned data and to minimize the granularity of the smallest change resulted in algorithms for compressing data at the granularity of a byte. Early algorithms were based upon either dynamic programming [19] or the greedy method [24, 21, 17] and performed this task using time quadratic in the length of the input files. Delta compression algorithms were improved to run in linear time and linear space. Algorithms with these properties have been derived from suffix trees [27, 18, 16] and as a generalization of Lempel Ziv data ....

W. F. Tichy. The string-to-string correction problem with block move. ACM Transactions on Computer Systems, 2(4), November 1984.

....solving some of the problems of dealing with this evolution. Pure version control systems such as sccs [22] and rcs [28, 30] using delta techniques to save storage space, keep track of the changes made by the different programmers to a file. Other space saving techniques have also been developed [8, 16, 18, 29]. Software configuration systems such as make [7] allow for the automatic reconfiguration of a system when changes are made to a component. Also, more detailed analysis of changes to components reduces much useless compiling [24, 31] Integrated systems attempt to combine these ideas. Among the ....

Walter F. Tichy. The string-to-string correction problem with block moves. ACM Transactions on Computer Systems, 2(4):309--321, Nov. 1984.

....substrings appear in V in the same order that they appear in R. Smaller cost edits exist if we permit substrings to be copied multiple times and if copied substrings from R may appear out of sequence in V . This problem, which is termed the string to string correction problem with block move [22], presents a model that represents both computation and I O costs for delta compression well. Traditionally, differencing algorithms have been based upon either dynamic programming [18] or the greedy algorithm [20] These algorithms solve the string to string correction problem with block move ....

....delta encoding of minimum cost is one that has the minimum number of copy commands. In such an encoding, the only use of add commands is to add symbols that do not appear in R. We consider perfect differencing to be the following version of the string to string correction problem with block move [22]: Given R and V , find a delta encoding of V having minimum cost under the simple cost measure. 3.1 A Greedy Differencing Algorithm We describe a greedy algorithm based on that of Reichenberger [20] within our framework. We use it as an example of a perfect differencing algorithm that will serve ....

W. F. Tichy. The string-to-string correction problem with block move. ACM Transactions on Computer Systems, 2(4), November 1984.

....to significant storage and transmission savings. This problem area is expected to become particularly important for small devices whose programs may need to be updated through slow expensive links (such as wireless) Computing differences between two text files has been studied extensively, e.g. [5, 4, 6, 7, 9]) and many algorithms have been designed and are deployed daily for the two purposes above. Computing such a difference is usually done by viewing the files as sequences of lines and applying a sequence comparison algorithm. Differences of executables are more complex, because a small change in ....

....values, but the particular set depends on the type of item. Example. Consider the item upgrade[8] in Figure 2. In order to recover it using the EqualValue scheme we search for the value of the matching item (original[10] Let us assume that O= f2;3;4;9g. Among those indices only item original[9] agrees in value. Its match, upgrade[7] contains the value 6, which we assume has been previously recovered. This is also the correct value for upgrade[8] 4. CloseValue. This is similar to the previous scheme, but more general, because we do not restrict ourselves to find an equal value within ....

Walter F. Tichy. The string-to-string correction problem with block moves. ACM Trans. on Comput. Syst., 2(4):309--321, 1984. 10

....A number of Unix utilities operate on differences between files. diff computes the difference between two text files. patch applies the output of diff to transform one file into the other. There have been studies of the problem of describing one file in terms of a minimal set of edits to another [22]. Mogul et al. 17] have investigated transmitting such deltas to save bandwidth when updating cached web pages. The CVS [1] version management system ships patches over the network to bring a user s working copy of a directory tree up to date. Unlike CVS, however, a file system cannot store a ....

Walter F. Tichy. The string-to-string correction problem with block moves. ACM Transactions on Computer Systems, 2(4):309--321, November 1984.

....of storing many versions of the same files. The technique is e#ective at reducing these requirements because one version of a file is typically similar to its successor or predecessor, often varying by only a few lines. For details on the algorithms employed to compute the di#erence file see [27, 28, 39], among others. The primary advantages of this design, other than the space saving e#ect, are that it is generally applicable (it can deal as easily with FORTRAN code as it does with a recipe collection) and it is straightforward to implement. This organization also leads naturally to the history ....

Walter F. Tichy. The string-to-string correction problem with block moves. ACM Transactions on Computer Systems, 2(4):309--321, November 1984.

....measure which is not related to SNN problems we study. 2. Block arrangements which involves moving a block (any consecutive set of characters) from one place to another; this is a rather natural notion in defining similarity of objects (such as in moving a paragraph of a text to another location [T84] or moving objects around in pen computing [LT96] or intrasequence rearrangements in genomic data [GD91] It also involves copying blocks from one place to another within a sequence, or deleting a copy of a block that exists elsewhere. These operations are motivated by data compression. 3. Block ....

W. F. Tichy, The string-to-string correction problem with block moves. ACM Trans. on Computer Systems, 2(4): 309-321, 1984.

...., and matching substrings appear in V in the same order that they appear in R. Smaller edits exist if we permit substrings to be copied multiple times and if copied substrings from R may appear out of sequence in V . This problem is termed the string to string correction problem with block move [19]. This formulation of the minimum cost edit between strings forms the basis for the development of efficient differencing algorithms. Traditionally, differencing algorithms have been based upon either dynamic programming [15] or the greedy algorithm [17] These algorithms solve the ....

....delta encoding of minimum cost is one that has the minimum number of copy commands. In such an encoding, the only use of add commands is to add symbols that do not appear in R. We consider perfect differencing to be the following version of the string to string correction problem with block move [19]: Given R and V , find a delta encoding of V having minimum cost under the simple cost measure. 3.1 Algorithms for Perfect Differencing Several existing algorithms for differencing input strings can solve the perfect differencing problem as defined above. Algorithms for this include techniques ....

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W. F. Tichy. The string-to-string correction problem with block move. ACM Transactions on Computer Systems, 2(4), November 1984.

....sequentially fail to emphasize the global similarity of two strings [6] Miller and Myers [9] established the limitations of LCS when they produced a new file compare program that executes at four times the speed of the diff program while producing significantly smaller deltas. The edit distance [14] proved to be a better metric for the difference of files and techniques based on this method enhanced the utility and speed of file differencing. The edit distance assigns a cost to edit operations such as delete a symbol , insert a symbol , and copy a symbol . For example, one longest common ....

....algorithm minimizes the edit distance to minimize the cost of a given string transformation. 1 A string substring contains all consecutive symbols between and including its first and last symbol whereas a sequence subsequence may omit symbols with respect to the corresponding string. 5 Tichy [14] adapted the string to string correction problem to file differencing using the concept of block move. Block move allows an algorithm to copy a string of symbols rather than an individual symbol. He then applied the algorithm to source code revision control package and created RCS [15] RCS ....

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TICHY, W. F. The string-to-string correction problem with block move. ACM Transactions on Computer Systems 2, 4 (Nov. 1984).

....Insert delete algorithms are less appropriate than copy insert algorithms for storage, transmission, and other mechanical purposes, although they are more appropriate for human viewing. Insert delete algorithms have inherently greater time complexity than the typical greedy copy insert algorithm [49], so in practice programs like diff break their input into line delimited records to reduce input size. This technique may be a reasonable approximation for text inputs, but it performs poorly in general on binary les. One study has already demonstrated copy insert algorithms that perform well on ....

....the source version length and N as the target version length. One simple, constant space approach that uses no auxiliary data structure at all resorts to a linear time search for every lookup operation; the resulting algorithm has time complexity O(MN ) The bdi algorithm uses a sux tree instead [49], which can be constructed in time and space proportional to the source version length, resulting in an algorithm with time complexity O(N M) and space complexity O(N ) Although the sux tree approach to string matching is optimal (using the simpli ed cost model) it has several disadvantages. ....

Tichy, W. F. The string-to-string correction problem with block moves. ACM Transactions on Computer Systems 2, 4 (Nov. 1984), 309-321.

....algorithm, neither during creation nor lookup. After building the suffix tree over the base version, the match process consists of scanning the variant, using the suffix tree to look up token sequences along the way. This is essentially the process used by Tichy in his bdiff delta compressor[13]; except, whereas his algorithm obtained the first best match from the suffix tree, this modified tree returns a list of all best matches. Thus an additional processing step is needed to chose which of the best matches to use for forming the longest upsequence. The solution to this problem was ....

W. F. Tichy. The string-to-string correction problem with block moves. ACM Transactions on Computer Systems, 2(4):309--654, November 1984.

....of characters. Only common lines can be found with diff. Since diff only produces output for text files, the contents of binary files must be folded into the ASCII printable range. A commonly used tool for this is uuencode. 3.3 Bdiff Bdiff is a modification of W. F. Tichy s block move algorithm[11]. It uses a twostage approach. First it computes the difference between the two files. Then it uses a second step to compress the resulting difference description. These two parts run concurrently in that the first stage calls the second each time it generates output. In the first phase, bdiff ....

....the window shifts, but does not need to build the suffix trees. Position information is given as an offset from the beginning of the window. 3.4 Vdelta Vdelta is a new technique that combines both data compression and data differencing. It is a refinement of W. F. Tichy s block move algorithm[11], in that, instead of a suffix tree, vdelta uses a hash table approach inspired by the data parsing scheme in the 1978 Ziv Lempel compression technique [14] Like blockmove, the Ziv Lempel technique is also based on a greedy approach in which the input string is parsed by longest matches to ....

Walter F. Tichy. The string-to-string correction problem with block moves. ACM Transactions on Computer Systems, 2(4):309--321, November 1984.

....binary code under revision control as well, not just source text. A simple technique is to map the binary code into text and then applying diff. While this works reliably and is widely used in practice, the deltas produced are typically larger than the originals Newer algorithms such as bdiff[10] and suff[8] do not exhibit this problem. Today, binary differencing capability has become mandatory. There are now many binary source formats that users need to manage such as word processor files, spreadsheet data, electrical and mechanical CAD data, sound, and images. Thus, revision control ....

....and higher dimensional data such as images and video data. In addition, this test suite could be used to fine tune both bdiff and vdelta, and to determine what effect postcompression has on run time and delta size. APPENDIX A. BDIFF Bdiff is a modification of W. F. Tichy s block move algorithm[10]. It uses a twostage approach. First it computes the difference between the two files. Then it uses a second step to compress the resulting difference description. These two parts run concurrently in that the first stage calls the second each time it generates output. In the first phase, bdiff ....

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Walter F. Tichy. The string-to-string correction problem with block moves. ACM Transactions on Computer Systems, 2(4):309--321, November 1984.

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W. F. Tichy, "The string-to-string correction problem with block moves," ACM Transactions on Computer Systems, vol. 2, no. 4, pp. 309--321, 1984.

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W. F. Tichy, The string-to-string correction problem with block moves. ACM Trans. on Computer Systems, 2(4): 309-321, 1984.

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W. F. Tichy. The string-to-string correction problem with block moves. ACM Trans. Computer Systems 2 (309--321) 1984. 15

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W. F. Tichy. The string-to-string correction problem with block moves. ACM Trans. Computer Systems 2 (309--321) 1984. 15

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W. F. Tichy. The string-to-string correction problem with block moves. ACM Trans. Computer Systems 2 (309-321) 1984. 22

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TICHY, W. F. The string-to-string correction problem with block moves. ACM Transactions on Computer Systems 2, 4 (Nov. 1984), 309--321.

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Tichy, W. "The String-to-String Correction Problem with Block Moves." ACM Transactions on Computer Systems 2, 4 (1984), 309-321.

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W. F. Tichy, `The string-to-string correction problem with block moves', ACM Trans. Computer Systems, 2, (4), 309--321 (1984).

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