Affix Files

The new system features an improved system for handling punctuation. As in the previous version, punctuation symbols are "stripped off" of words, in that a space is inserted between the symbol and a neighboring word; they can then be treated like ordinary words, and linked to other words or to the wall. In the new version, however, the symbols to be stripped off in this way can easily be specified and modified by the user, using an "affix file" which is read in by the parser when the program is run. An affix file is similar in format to a link grammar dictionary, with lists of strings (they need not be individual symbols, but may be any length), followed by a connector type. Strings to be stripped off from the left are listed under the category "LSTRIP+"; those to be stripped off from the right are listed under the category "RSTRIP+". In the affix-file that we provide, for example, "$" is listed as a "LSTRIP+" symbol; "," is listed as a "RSTRIP+" symbol. When listed in the affix-file, punctuation symbols must be surrounded by quotation marks.

It may also be useful to list other things besides punctuation symbols in the affix file. In the version 4.0 affix-file that we provide, strings such as "'re" and "'ll" are also listed in the RSTRIP+ category, so that they too are stripped off from the right end of strings. Thus the sentence "you're crazy if you think he'll do it" is parsed like this:

 +Spx+-Paf-+-MVs-+Cs+--Sp-+--Ce-+Ss+--I-+-Ox+
 |   |     |     |  |     |     |  |    |   |
you 're crazy.a if you think.v he 'll do.v it

One advantage of this is that the phrase-parser is then able to insert a phrase boundary between "you" and "'re":

[S [NP You NP] [VP 're [ADJP crazy ADJP] VP] [SBAR if [S [NP you NP] [VP think  
[SBAR [S [NP he NP] [VP 'll [VP do [NP it NP] VP] VP] S] SBAR] VP] S] SBAR] S] 

PRE+ and SUF+.Two other categories may also be used in the affix file, "PRE+" and "SUF+". These are similar to "LSTRIP+" and "RSTRIP+", but with a difference. A string listed under "PRE+" will get stripped off of the left end of a word, but only if the remainder of the word is not listed in the dictionary; the "SUF+" category is similar, except for right-strippable strings.

While we do not PRE+ and SUF+ in the current English parser, they may be useful for other languages, for example to handle inflectional word endings. We use them in a small way in the German dictionary that we provide. Adjective endings are listed as "SUF+" strings; these are then stripped off (assuming that the total word "stem+ending" is NOT listed in the dictionary, and that remainder of the word IS listed as a word in the dictionary). Adjective stems and endings can then be listed independently, rather than listing all possible combinations. When an adjective+ending is typed in, the ending is stripped off and treated as a separate word; it is then linked to the stem with an "FS" link. For example, the sentence "Die schwarze Katze lief" produces this:

linkparser> die schwarze Katze lief
++++Time                                          0.00 seconds (0.00
total)
Found 1 linkage (1 had no P.P. violations)
  Unique linkage, cost vector = (UNUSED=0 DIS=0 AND=0 LEN=12)

    +-----------------W----------------+
    |       +--------Dnf-------+       |
    |       |       +----Ae----+       |
    |       |       +-FSe-+    +---Ss--+
    |       |       |     |    |       |
LEFT-WALL die.d schwarz.a e Katze.n lief.s

Notice that the ending "e" is NOT stripped off of the word "Katze"; this is because that word is listed in the dictionary as a whole.