LZW: rebuilding a compression dictionary as data arrives

What changed

Scientific scope

Welch presents a practical adaptive dictionary compressor that sends codes for previously encountered strings while its decoder reconstructs the dictionary, with simple mechanisms suited to high-throughput storage systems. The target is the 1984 LZW engineering construction and system analysis, not the earlier LZ 77/LZ 78 universal-coding theory or all later file formats and patents. Lossless decoding needs the same initial alphabet and code-assignment conventions, including the newly-created-code special case. Practical dictionary capacity, reset/extension policy and bit packing require an agreed format. A common 12-bit implementation is an example, not a universal code width. Short inputs can expand by 50% initially; some tested floating-point arrays expand, and changing data statistics or a full table affect compression. Reported ratios cover several Lempel-Ziv variants and imperfectly comparable data, not one uniformly superior algorithm. Variable compressed lengths, buffering, error propagation and random-access integration remain costs. The source does not assert optimal parsing or every-input compression. Later deployment evidence is not inherited automatically.

Evidence

Source-linked, scoped account of the original work. The published scope states the scientific assumptions and remaining verification limits. WRS has not independently certified the full proof, experimental result or system benchmark.

Contributors

Terry A. Welch · SCIENCE: Original source-listed scientific author of this scoped work; byline does not determine effort fractions.

Terry A. Welch, A Technique for High-Performance Data Compression (Computer 17(6),8-19, June 1984), original scan

Provisional WRS assessment, edition 2026-10-16.1. Independent expert calibration is pending. This grade does not certify correctness or assign ownership.

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