cvs diff -u search.module (in directory C:\CVS\drupalpatch\modules\)
Index: search.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/search.module,v
retrieving revision 1.125
diff -u -r1.125 search.module
--- search.module	23 Apr 2005 07:34:22 -0000	1.125
+++ search.module	23 Apr 2005 08:49:29 -0000
@@ -380,6 +380,9 @@
               $linknid = $match[1];
               if ($linknid > 0) {
                 $link = true;
+                // A link counts as a general score boost for the target page.
+                // The words used for the link caption also count (see below).
+                $results[$linknid][''] += 1;
               }
             }
           }
@@ -523,8 +526,35 @@
   }
   $count_query = "SELECT $count";
 
-  // Do pager query
-  $query = "SELECT i.type, i.sid, SUM(i.score/t.count) AS score FROM {search_index} i $join INNER JOIN {search_total} t ON i.word = t.word WHERE $conditions GROUP BY i.type, i.sid ORDER BY score DESC";
+  /*
+    Do pager query
+
+    The search index consists of the unique words in a piece of content (e.g. a
+    node), and the words' scores (see search_index() to see how they are
+    calculated).
+
+    To find items, we find all matching keywords and divide each word's absolute
+    score in a particular item by the sum of all scores for this word (cached in
+    search_total) to get a relative score. All the relative scores are then
+    summed per item and the result is used as a ranking key for the results.
+
+    The search indexer also takes note of links to items (for now only nodes)
+    and assigns extra link scores to items under an empty word. These extra
+    scores are fetched with a LEFT JOIN on another table. 
+    
+    Each link counts for 0.02. Experience shows that on a good database, good
+    results score between 0.20 and 0.40, while great results are above 0.40.
+    In theory the ranking score is unbounded, as more keywords equal
+    more scores to sum, but in practice long queries tend to be vagues and 
+    contain more noise words. Thus the ranking score rarely goes above 1.0. When
+    it does, the results are usually very relevant already so link boosting is
+    unnecessary.
+
+    Aside from the general link boost, the scores for a link's text are also
+    added to the target item's total. However, this is handled transparently by
+    simply indexing them directly with the item they link to.
+  */
+  $query = "SELECT i.type, i.sid, (SUM(i.score/t.count) + MAX(if(j.word IS NULL, 0, j.score))*0.02) AS score FROM {search_index} i $join INNER JOIN {search_total} t ON i.word = t.word LEFT JOIN {search_index} j ON i.sid = j.sid AND j.word = '' WHERE $conditions GROUP BY i.type, i.sid ORDER BY score DESC";
   $result = pager_query($query, 15, 0, $count_query, $arguments);
 
   $results = array();