Data Searching is a very complex art in itself. Ignoring the long history of Internet "search engines" growing from Archie in 1992 to today's Google engine. Original techniques to provide users with "full text" search required a solution designed for common mistakes, one of which is called Soundex.

     Soundex is a phonetic algorithm for indexing words by sound as pronounced in American English. The goal of course was to encode homophones to the same representation so they could be matched despite minor differences in spelling. Unfortunately Soundex is probably the most used algorithm used in data searching and is often used incorrectly. Soundex is quite simple:

Code snippet from DXSock 6.0 WLM (Courtesy of Brain Patchwork DX, LLC)

function SoundEx(Const S: string): string;
const
   Table: array[1..26] of Char = '.123.12..22455.12623.1.2.2';

var
   SoundString: string[255];
   I1: Integer;
   I2: Integer;
   isNum: boolean;
   Ch: Char;
   Str:String;
   MaxLoop:Integer;

begin
   Result := S;
   if S = '' then Exit;
   Str:=S;
   isNum := true;
   repeat
      Ch := UpCase(S[1]);
      if Ch > #64 then isNum := false
      else Delete(Str, 1, 1);
   until (isNum = false) or (Str = '');
   Result := Str;
   if Str = '' then Exit;
   SoundString[0] := #255;
   FillChar2(SoundString[1], 255, '0');
// Step 1: ASCII to Soundex
{$IFDEF ASSEMBLY}
   asm // 1090108: By Ozz (FASTER THAN Length()!)
     MOV EAX, S;       // Store Str Address
     MOV EAX, [EAX-$04]; // Move to "Size" Int32
     MOV MaxLoop, EAX;    // Put into Result
   End;
{$ELSE}
   MaxLoop:=Length(S);
{$ENDIF}
   for I1 := 1 to MaxLoop - 1 do begin
      I2 := Ord(UpCase(S[I1 + 1])) - 64;
      if ((I2 < 1) or (I2 > 26)) then I2 := 1;
      SoundString[I1] := Table[I2];
   end;
// Initialize for second pass
   I1 := 1;
   repeat
      while (SoundString[I1] = '.') do
         Delete(SoundString, I1, 1);
      while ((SoundString[I1] = SoundString[I1 + 1]) and (SoundString[I1] <> '0')) do
         Delete(SoundString, I1, 1);
      Inc(I1);
   until (SoundString[I1] = '0');
   Result := Ch + Copy(SoundString, 1, 3);
end;

     Using this algorithm, both "Robert" and "Rupert" return the same string "R163" while "Rubin" and "Robin" yields "R150". "Ashcroft" and "Ashcraft" yields "A226". However, "George" and "Jorge" yields "G620" and "J620" and "Dave" and "David" yields "D100" and "D130".

     This simple example shows a need for other comparison algorithms. Read more on other comparison techniques I used in my search engines.

G.E. Ozz Nixon Jr.

Matias Vara
toro.sourceforge.net