This facility searches for records containing strings which either exactly or approximately match a pattern. Approximate matching allows finding records that contain the pattern with several errors including substitutions, insertions, and deletions. For example, Massechusets matches Massachusetts with two errors (one substitution and one insertion).

Our search supports many kinds of queries including arbitrary wild cards, sets of patterns, and in general, regular expressions. It supports a large variety of patterns, including simple strings, strings with classes of characters, sets of strings, wild cards, and regular expressions.

Strings

Any sequence of characters, including the special symbols ‘^’ for beginning of line and ‘$’ for end of line. The special characters ( ‘$’, ‘^’, ‘*’, ‘[’, ‘^’, ‘|’, ‘(’, ‘)’, ‘!’, and ‘\’ ) should be preceded by ‘\’ if they are to be matched as regular characters. For example, \^abc\\ corresponds to the string ^abc\, whereas ^abc corresponds to the string abc at the beginning of a line.

Classes of characters

A list of characters inside [] (in order) corresponds to any character from the list. For example, [a-ho-z] is any character between a and h or between o and z. The symbol ‘^’ inside [] complements the list. For example, [^i-n] denote any character in the character set except character ‘i’ to ‘n’. The symbol ‘^’ thus has two meanings, but this is consistent with other searches. The symbol ‘.’ (don't care) stands for any symbol (except for the newline symbol).

Boolean operations

The search supports an ‘and’ operation ‘;’ and an ‘or’ operation ‘,’, but not a combination of both. For example, ‘fast;network’ searches for all records containing both words.

Wild cards

The symbol ‘ # ’ is used to denote a wild card.  #  matches zero or any number of arbitrary characters. For example, ex#e matches example. The symbol  #  is equivalent to .* as used in other searches. In fact, .* will work too, because it is a valid regular expression (see below), but unless this is part of an actual regular expression,  #  will work faster.

Combination of exact and approximate matching

Any pattern inside angle brackets <> must match the text exactly even if the match is with errors. For example, <mathemat>ics matches mathematical with one error (replacing the last s with an a), but mathe<matics> does not match mathematical no matter how many errors we allow.

Regular expressions

The syntax of regular expressions in our search is in general the same as that for other searches. The union operation ‘|’, Kleene closure ‘*’, and parentheses () are all supported. Currently ‘+’ is not supported. Regular expressions are currently limited to approximately 30 characters (generally excluding meta characters).