Both iTap and T9 use the mapping mentioned below, and I wasn't careful to distinguish between the two products when I wrote this page, because I wasn't familiar with the difference between iTap and T9. But I have now been informed: iTAP and T9 are two different products, and compete with each other. T9 is created by Tegic, a company in Seattle, and is used on most Nokia phones. iTAP is a product of a division of Motorola in Silicon Valley. For a list of differences between iTap and T9, see bottom of page.
The "iTap/T9" code for English encodes the characters [A-Z] into the characters [2-9] using this mapping:
sub encode {
s/[ABC]/2/g;
s/[DEF]/3/g;
s/[GHI]/4/g;
s/[JKL]/5/g;
s/[MNO]/6/g;
s/[PQRS]/7/g;
s/[TUV]/8/g;
s/[WXYZ]/9/g;
}
[This mapping is the one that has been used on telephones for decades.]
The patented T9 system uses a dictionary (does it also use a general language model?) to decode the string back into english characters. In the event of any ambiguity, the user uses scroll commands (embodied on one or more other keys) to select the desired word from a list offered by the machine.
I was curious to find out how good this code is for English. I could see it being bad in two possible ways.
I used a perl program and the linux dictionary /usr/dict/words: I found that 45373 distinct words mapped to 41439 distinct codes, and 3934 clashes occurred. So if the user picks words at random from the dictionary and the system knows all those words and no others, then the disambiguator will have to be used for less than 10% of words. In fact, for even fewer than that, if the first guess made by T9 is correct, as is often the case. [Dale Grover told me that in practice T9 gets it right better than 97% of the time.]
Here are some of the worst clashes (i.e. clashes involving most words). I note with a smile that the two examples chosen by Motorola (HELLO) and Tegic (HOW) do not suffer clashes with any dictionary words.
ACRES, BARDS, BARER, BARES, BASER, BASES, CAPER, CAPES, CARDS, CARES, CASESThe worst-case number of keypresses that the user has to make, given a dictionary word, is thus ten scroll-commands on top of the original word. That does not seem excessive, though I can imagine that people who send messages about acres, bases, cards, cares and cases, all of which are fairly frequent five-letter words, might get a little bored of having to do this. But it is certainly better than the multi-tap code!
A few of the more amusing (though not if your name is Amy) confusable sets are:
269 : AMY, ANY, BOW, BOX, BOY, COW 7467 : PIMP, PINS, RIMS, SHOP, SIMS, SINS 25663 : ALONE, ALOOF, BLOND, BLOOD, CLONE 74687 : PINTS, PIOTR, PIOUS, RIOTS, SHOTS, SINUS 5477 : KISS, LIPS, LISP, LISS
729 : PAW, PAY, PAZ, RAW, RAY, SAW, SAX, SAY 76737 : PORES, POSER, POSES, ROPER, ROPES, ROSES, SORER, SORES 46637 : GONER, GOODS, GOOFS, HOMER, HOMES, HONER, HONES, HOODS, HOOFS, INNER 22737 : ACRES, BARDS, BARER, BARES, BASER, BASES, CAPER, CAPES, CARDS, CARES, CASES 7283 : PATE, PAVE, RATE, RAVE, SATE, SAUD, SAVE, SCUD 2273 : ACRE, BARD, BARE, BASE, CAPE, CARD, CARE, CASE
4663 : GONE, GOOD, GOOF, HOME, HONE, HOOD, HOOF 726 : PAM, PAN, RAM, RAN, SAM, SAN, SAO 72837 : PAVES, RATER, RATES, RAVES, SATES, SAVER, SAVES 227837 : BARTER, BASTES, CARTER, CARVER, CARVES, CASTER, CASTES 2277 : BARR, BARS, BASS, CAPS, CARP, CARR, CARS 752837 : PLATES, SKATER, SKATES, SLATER, SLATES, SLAVER, SLAVES 7867 : PUMP, PUNS, RUMP, RUNS, STOP, SUMS, SUNS
2877 : BURP, BURR, BUSS, CUPS, CURS, CUSP 742737 : PHASER, PHASES, SHAPER, SHAPES, SHARER, SHARES 786 : PUN, QUO, RUM, RUN, SUM, SUN 34637 : DIMES, DINER, DINES, FINDS, FINER, FINES 26637 : BONDS, BONER, BONES, COMER, COMES, CONES 787433 : PURGED, PUSHED, RUSHED, STRIDE, STRIFE, SURGED 787437 : PURGES, PUSHER, PUSHES, RUSHER, RUSHES, SURGES 7243 : PAGE, PAID, RAGE, RAID, SAGE, SAID 74687 : PINTS, PIOTR, PIOUS, RIOTS, SHOTS, SINUS 7277 : PARR, PARS, PASS, RAPS, RASP, SAPS 7627 : ROAR, ROBS, SNAP, SOAP, SOAR, SOBS 7673 : POPE, PORE, POSE, ROPE, ROSE, SORE 27437 : ARIES, ASHER, ASHES, BRIER, CRIER, CRIES 26737 : BORER, BORES, COPES, CORDS, CORER, CORES 2253 : ABLE, BAKE, BALD, BALE, CAKE, CALF 2263 : ACME, ACNE, BAND, BANE, CAME, CANE 74337 : RIDER, RIDES, SHEDS, SHEEP, SHEER, SIDES 2666 : AMMO, ANON, BONN, BOOM, BOON, COON 529 : JAW, JAY, KAY, LAW, LAX, LAY 7327 : PEAR, PEAS, REAP, REAR, SEAR, SEAS 7337 : PEEP, PEER, REDS, SEEP, SEER, SEES 782537 : PUCKER, QUAKER, QUAKES, RUBLES, STAKES, SUCKER 269 : AMY, ANY, BOW, BOX, BOY, COW 22537 : ABLER, BAKER, BAKES, BALER, BALES, CAKES 7463 : PINE, RIME, RIND, SHOD, SHOE, SINE 7467 : PIMP, PINS, RIMS, SHOP, SIMS, SINS
3937 : DYER, DYES, EWES, EYER, EYES 763 : POD, POE, ROD, ROE, SOD 769 : POX, ROW, ROY, SOW, SOY 32837 : DATER, DATES, EATER, EAVES, FATES 72437 : PAGER, PAGES, RAGES, RAIDS, SAGES 54637 : KHMER, KINDS, LIMES, LINER, LINES 272837 : BRAVER, BRAVES, CRATER, CRATES, CRAVES 72833 : PAVED, RATED, RAVED, SATED, SAVED 486 : GUM, GUN, HUM, HUN, ITO 7263 : PANE, RAND, SAME, SAND, SANE 7297 : PAWS, PAYS, RAYS, SAWS, SAYS 7653 : POKE, POLE, ROLE, SOLD, SOLE 7687 : POTS, POUR, ROTS, SOUP, SOUR 25663 : ALONE, ALOOF, BLOND, BLOOD, CLONE 42779 : GARRY, GASSY, HAPPY, HARPY, HARRY 73257 : PEAKS, PEALS, PECKS, REALS, SEALS 72537 : PALER, PALES, RAKES, SAKES, SALES 372737 : DRAPER, DRAPES, ERASER, ERASES, FRASER 2663 : ANNE, BOND, BONE, COME, CONE 2673 : BORE, BOSE, COPE, CORD, CORE 7282437 : PATCHES, RAVAGER, RAVAGES, SAVAGER, SAVAGES 74737 : PIPER, PIPES, RISER, RISES, SIRES 76537 : POKER, POKES, POLES, ROLES, SOLES 7325 : PEAK, PEAL, PECK, REAL, SEAL 6277 : MAPS, MARS, MASS, NAPS, OARS 4867 : GUMS, GUNS, HUMP, HUMS, HUNS 72237 : PACER, PACES, RACER, RACES, SABER 2337 : ADDS, BEDS, BEEP, BEER, BEES 5263 : JANE, KANE, LAME, LAND, LANE 5277 : JARS, KARP, LAPS, LARS, LASS 728464 : PAVING, RATING, RAVING, SATING, SAVING 42937 : GAYER, GAZER, GAZES, HAYES, HAZES 2427 : AGAR, BIAS, BIBS, CHAP, CHAR 26937 : BOWER, BOWES, BOXER, BOXES, COWER 2433 : AGED, AGEE, AIDE, BIDE, CHEF 2437 : AGER, AGES, AIDS, BIDS, BIER 72737 : PAPER, PARES, RAPER, RAPES, RARER 5337 : JEEP, JEER, KEEP, LEER, LEES
2867 : ATOP, BUMP, BUMS, BUNS 4653 : GOLD, GOLF, HOLD, HOLE 6453 : MIKE, MILD, MILE, NILE 739 : PEW, REX, SEW, SEX 746 : PIN, RHO, RIM, RIO 747 : PIP, RIP, SIP, SIR 726737 : PAMPER, SCOPES, SCORER, SCORES 9327 : WEAR, WEBS, YEAR, YEAS 782 : PUB, QUA, RUB, SUB 762733 : ROARED, SNARED, SOAPED, SOARED 2877464 : BURPING, BUSSING, CUPPING, CURSING 2527 : AJAR, ALAR, ALAS, CLAP 36837 : DOTES, DOVER, DOVES, ENTER 46639 : GOMEZ, GOODY, GOOFY, HONEY 74273 : PHASE, SHAPE, SHARD, SHARE 767837 : PORTER, POSTER, ROSTER, SORTER 3637 : DOER, DOES, ENDS, FOES 4367 : GEMS, HEMP, HEMS, HENS 426 : HAM, HAN, IAN, IBN 427 : GAP, GAS, HAP, HAS 74637 : PINES, RINDS, SHOES, SINES 3262437 : DAMAGER, DAMAGES, FANCIER, FANCIES 3663 : DOME, DONE, FOND, FOOD 3673 : DOPE, DOSE, FORD, FORE 472837 : GRATER, GRATES, GRAVER, GRAVES 5463 : KIND, LIME, LIND, LINE 7253 : PALE, RAKE, SAKE, SALE 4747 : GRIP, GRIS, IRIS, ISIS 5477 : KISS, LIPS, LISP, LISS 78253 : QUAKE, RUBLE, STAKE, STALE 92837 : WATER, WAVER, WAVES, YATES 22733 : BARED, BASED, CARED, CASED 6833537 : MUDDLER, MUDDLES, MUFFLER, MUFFLES 7688464 : POTTING, POUTING, ROTTING, ROUTING 287733 : BURPED, BUSSED, CUPPED, CURSED 26337 : ANDES, BODES, CODER, CODES 227437 : BARGES, BASHES, CASHER, CASHES 7663 : POND, ROME, ROOF, SOME 7667 : POMP, POOR, ROMP, SONS 7627464 : ROARING, SNARING, SOAPING, SOARING 227464 : BARING, BASING, CARING, CASING 27433 : ASIDE, BRIDE, BRIEF, CRIED 44537 : GILDS, GILES, HIKER, HIKES 2267 : ABOS, BANS, CAMP, CANS 2275 : BARK, BASK, CARL, CASK 722537 : PACKER, SABLES, SACKER, SCALES 73277 : PEARS, REAPS, REARS, SEARS 2639 : ANDY, ANEW, BODY, CODY 2647 : BOGS, BOHR, BOIS, COGS 2653 : BOLD, COKE, COLD, COLE 367243 : DOSAGE, ENRAGE, FORAGE, FORBID 75433 : PLIED, SKIED, SKIFF, SLIDE 2662 : ANNA, BOMB, BOOB, COMB 2665 : AMOK, BOOK, COOK, COOL 2667 : AMOS, BOOR, BOOS, COOP 7338237 : REDUCER, REDUCES, SEDUCER, SEDUCES 742537 : PICKER, SHAKER, SHAKES, SICKER 22437 : ACHES, ACIDS, CAGER, CAGES 546 : JIM, KIM, KIN, LIN 66737 : MORES, MOSER, MOSES, NOSES 7335 : PEEK, PEEL, REEL, SEEK 78337 : PUFFS, QUEER, STEEP, STEER 7363 : PEND, REND, RENE, SEND 762533 : ROCKED, SNAKED, SOAKED, SOCKED 87437 : TRIER, TRIES, URGES, USHER 7378 : PERU, PEST, REST, SEPT 22837 : BATES, BAUER, CATER, CAVES 94737 : WIPER, WIPES, WIRES, WISER 75867 : PLUMP, PLUMS, SLUMP, SLUMS 8437 : TIER, TIES, VIER, VIES 3678437 : EMPTIER, EMPTIES, FORTIER, FORTIES 966 : WON, WOO, YON, ZOO 729464 : PAWING, PAYING, SAWING, SAYING 6333537 : MEDDLER, MEDDLES, NEEDLER, NEEDLES 52637 : JAMES, LAMES, LANDS, LANES 42837 : GATES, HATER, HATES, HAVES 72257 : PACKS, RACKS, SACKS, SCALP 2278464 : BASTING, CARTING, CARVING, CASTING 7225464 : PACKING, RACKING, SACKING, SCALING 73337 : REEDS, REEFS, REFER, SEEDS 2682437 : BOTCHER, BOTCHES, BOUCHER, COUCHES 73357 : PEEKS, PEELS, REELS, SEEKS 73377 : PEEPS, PEERS, SEEPS, SEERS 226 : ABO, BAN, CAM, CAN 228 : ABU, ACT, BAT, CAT 64637 : MINDS, MINER, MINES, NINES 54837 : KITES, LITER, LIVER, LIVES 3463 : DIME, DINE, FIND, FINE 7335464 : PEEKING, PEELING, REELING, SEEKING 768733 : POURED, ROUSED, SOUPED, SOURED 72687 : PANTS, RANTS, SCOTS, SCOUR 266 : ANN, BOO, CON, COO 76277 : ROARS, SNAPS, SOAPS, SOARS 627537 : MAPLES, MARKER, MASKER, NAPLES 7874464 : PURGING, PUSHING, RUSHING, SURGING 633 : NED, ODD, ODE, OFF 24337 : AIDES, CHEER, CHEFS, CIDER 7426 : RICO, SHAM, SIAM, SIAN 5646 : JOHN, JOIN, LOGO, LOIN 7866464 : RUNNING, STONING, SUMMING, SUNNING 7455 : PILL, RILL, SILK, SILL 5673 : JOSE, LORD, LORE, LOSE 7473 : PIPE, RIPE, RISE, SIRE 7477 : PISS, RIPS, SIPS, SIRS 727737 : PARSER, PARSES, PASSER, PASSES 32733 : DARED, EARED, EASED, FARED 32737 : DARER, DARES, EASES, FARES 96637 : WOODS, WOOER, WOOFS, ZONES 7827 : PUBS, RUBS, STAR, SUBS 25837 : ALTER, BLUER, BLUES, CLUES 7877 : PUPS, PURR, PUSS, RUSS 262937 : AMAZER, AMAZES, COAXER, COAXES 46537 : GOLDS, HOLDS, HOLES, INKER 36737 : DOPER, DOPES, DOSES, FORDS 347437 : DIRGES, DISHES, FISHER, FISHES 82537 : TAKER, TAKES, TALES, VALES 732533 : PEAKED, PEALED, PECKED, SEALED 327 : DAR, EAR, FAQ, FAR 786633 : RUNOFF, STONED, SUMMED, SUNNED 786637 : RUNNER, STONES, SUMMER, SUMNER 4283 : GATE, GAVE, HATE, HAVE 346 : DIM, DIN, EGO, FIN 75283 : PLATE, SKATE, SLATE, SLAVE 2833 : BUDD, BUFF, CUED, CUFF