Parallel development has become standard practice in software development and maintenance. Though almost every revision control and configuration management system provides some form of merging for combining changes made in parallel, these mechanisms often yield unsatisfactory results. The authors present a new merging algorithm, that uses a fast differencing algorithm and renaming analysis to provide better merge results. The system is language aware, but not language dependent and does not require a special editor so it can be easily integrated in current development environments.

The current suite of systems that offer client/server capabilities for document versioning relies on proprietary protocols for communicating between a central versioning repository and a remote client. In order to support better document authoring via the Web, the DeltaV working group of the WebDAV (WWW Distributed Authoring and Versioning) project of the Internet Engineering Task Force is working on a standard protocol for versioning over HTTP. The authors present a prototype of DeltaV based on the 04.5 draft. This system demonstrates that, though important aspects of the protocol need to be revised, versioning via the Web can be a practical means of supporting remote access to a central versioning repository.

Finding changed identifiers in programs is important for program comparison and merging. Comparing two versions of a program is complicated if renaming has occurred. Textual merging is highly unreliable if, in one version, identifiers were renamed, while in the other version, code using the old identifiers was added or modified. A tool that automatically detects renamed identifiers between pairs of program modules is presented. The detector is part of a suite of intelligent differencing and merging programs that exploit the static semantics of programming languages. No special editor is needed for tracking changes. The core of the renaming detector is language independent. The detector works with multiple file pairs, taking into account renamings that affect multiple files. Renaming detectors for Java and Scheme have been implemented. A case study is presented that demonstrates proof of concept. With renaming detection, a higher quality of program comparison and merging is achievable.

The authors supply machine configurations for experiments reported in “Delta Algorithms: An Empirical Analysis,” by Hunt et al. (ACM Trans. Softw. Eng. Methodol. 7, 2 (Apr. 1998), pp. 192-214).

Delta algorithms compress data by encoding one file in terms of another. This type of compression is useful in a number of situations: strong multiple versions of data, displaying differences, merging changes, distributing updates, storing backups, transmitting video sequences, and others. This article studies the performance parameters of several delta algorithms, using a benchmark of over 1,300 pairs of files taken from two successive releases of GNU software. Results indicate that modern delta compression algorithms based on Ziv-Lempel techniques significantly outperform diff , a popular but older delta compressor, in terms of compression ratio. The modern compressors also correlate better with the actual difference between files without sacrificing performance.