Unni Cathrine Eiken February 2005

The Prolog code extract in (3-13) shows the MRS representation of the sentence in (3-12) by
listing all the EPs in the sentence as well as the relationships that hold between the individual
EPs. In simplified terms, the value of the attribute ‘semform’ holds the semantic form of the
predicate, and the values of ‘ARG1’ and ‘ARG2’ point to the EPs where the semantic forms for
argument 1 and argument 2 can be found. In order to extract all EPAS from such a Prolog file,
one must go through all the EPs in turn, and find the semantic forms of each main EP and its
belonging argument 1 and argument 2. In the extraction process, this matching and tracing of
values is performed by the script Ekstraktor.
The algorithm behind Ekstraktor is divided into two more or less separate parts: information
retrieval from the Prolog file and processing of the information that was found and stored. Perl
was chosen as the programming language mainly because of its excellent pattern matching
facilities. Perl offers a very powerful and flexible regular expression syntax which lets the
programmer construct regular expressions that will handle all kinds of pattern matching. For the
information retrieval part of Ekstraktor, it was desirable to go through an input file, check for
various patterns and store parts of the input file relevant to how the patterns were matched. (3-
14) shows one of the pattern checks in Ekstraktor – if the line read from the file contains the
string:
‘relation’),semform(
the entire line is stored in the array semform.
(3- 14)
if ($linjeFraFil =~ m/'relation'\),semform\(/){
push(@semform, $linjeFraFil);
}
By going through the input file line by line and checking for several patterns, all information
relevant to extracting the EPAS is stored in a system of arrays. To be able to keep track of which
EP the various values belong to, a system of two arrays for each argument type is used – one for
EP number and one for argument value. The ARG0 arrays correspond to the predicates in the
structures and for each, the semantic form can directly be found in the semform-array. The
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