RE: Textual transmission typically faster?
1/21/01 6:48:39 PM, Danny Ayers <danny@p...> wrote: >An example of a binary format reducing interoperability is MS compressed >HTML. This is used in some Windows help systems, but is out of reach to >other systems such as JavaHelp. It seems unlikely however that MS came up >with this format with efficiency in mind, copyright paranoia perhaps being a >more likely motivation. This is just speculation, but I suspect the motivation was a sort of inertia: the new MS HTML help system uses a highly compressed format because the old MS RTF-based help system used a highly compressed format so compression became The Way We've Always Done It, despite the fact that the conditions that made heavy compression a sensible decision Way Back When (memory and disk space were expensive, and you needed tricky code to access any data structure over 64K) no longer exist. As far as "optimization" of data formats goes in general, remember that the law of evolution known as Fisher's Fundamental Theorem of Natural Selection applies to human inventions as well as biological organisms. It says that the better adapted an organism is to its current environment, the less change in its environment it can survive. In the realm of data formats, this means that the effort spent optimizing a data format is likely to be wasted as soon as the data to be conveyed changes, because the optimization took advantage of what were effectively limitation on the data to be conveyed. Gerald Weinberg tells the story of a group that was writing an assembler for an early computer. They managed to come up with a perfect hash function that could map all the machine's opcodes into single-byte codes, thus avoiding the overhead of chaining or probing. They were really proud of their ingenuity, but then the next version of the hardware came out, adding a couple new opcodes, and there was no longer any perfect hash for them. The group had to replace their carefully-optimized code with a standard hash-table lookup; if they had done that in the first place, a lot of wasted effort would have been saved.
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