Wais - access to freeWAIS-sf libraries

require Wais;

The interface is divided in four major parts.

SFgate 4.0

For backward compatibility the functions used in SFgate up to version 4 are still present. Their use is deprecated and they are not documented here. These functions may no be supported in following versions of this module.

Protocol

XS functions which provide a low-level access to the WAIS protocol. E.g. generate_search_apdu() constructs a request message.

SFgate 5

Perl functions that implement high-level access to WAIS servers. E. g. parallel searching is supported.

dictionary

A bunch of XS functions useful for inspecting local databases.

We will start with the SFgate 5 functions.

The main high-level interface are the functions Wais::Search and Wais::Retrieve. Both return a reference to an object of the class Wais::Result.

Arguments of Wais::Search are hash references, one for each database to search. The keys of the hashes should be:

query

The query to submit.

database

The database which should be searched.

host

host is optional. It defaults to 'localhost'.

port

port is optional. It defaults to 210.

tag

A tag by which individual results can be associated to a database/host/port triple. If omitted defaults to the database name.

relevant

If present must be a reference to an array containing alternating document id's and types. Document id's must be of type Wais:Docid.

Here is a complete example:

     $result = Wais::Search({'query'    => 'pfeifer', 
                             'database' => $db1, 
                             'host'     => 'ls6',
                             'relevant' => [$id, 'TEXT']},
                            {'query'    => 'pfeifer', 
                             'database' => $db2});

If host is 'localhost' and database.src exists, local search is performed instead of connecting a server.

Wais::Search will open $Wais::maxnumfd connections in parallel at most.

Wais::Retrieve should be called with named parameters (i.e. a hash). Valid parameters are database, host, port, docid, and type.

        $result = Wais::Retrieve('database' => $db,
                                 'docid'    => $id, 
                                 'host'     => 'ls6',
                                 'type'     => 'TEXT');

Defaults are the same as for Wais::Search. In addition type defaults to 'TEXT'.

The functions Wais::Search and Wais::Retrieve return references to objects blessed into Wais:Result. The following methods are available:

diagnostics

Returns and array of diagnostic messages. Each element (if any) is a reference to an array consisting of

tag

The tag of the corresponding search request or 'document' if the request was a retrieve request.

code

The WAIS diagnostic code.

message

A textual diagnostic message.

header

Returns and array of WAIS document headers. Each element (if any) is a reference to an array consisting of

tag

The tag of the corresponding search request or 'document' if the request was a retrieve request.

score

lines

Length of the corresponding dcoument in lines.

length

Length of the corresponding document in bytes.

headline

types

A reference to an array of types valid for docid.

docid

A reference to the WAIS identifier blessed into Wais::Docid.

text

Returns the text fetched by Wais::Retrieve.

There are a couple of functions to inspect local databases. See the inspect script in the distribution. You need the Curses module to run it. Also adapt the directory settings in the top part.

       %frequency = Wais::dictionary($database);
       %frequency = Wais::dictionary($database, $field);
       %frequency = Wais::dictionary($database, 'foo*');
       %frequency = Wais::dictionary($database,  $field, 'foo*');

The function returns an array containing alternating the matching words in the global or field dictionary matching the prefix if given and the freqence of the preceding word. In a sclar context, the number of matching word is returned.

The function takes the same arguments as Wais::dictionary. It returns the same array rsp. wordcount with the word frequencies replaced by the offset of the postinglist in the inverted file.

       %postings = Wais::postings($database, 'foo');
       %postings = Wais::postings($database, $field, 'foo');

Returns and an array containing alternating numeric document id's and a reference to an array whichs first element is the internal weight if the word with respect to the document. The other elements are the word/character positions of the occurances of the word in the document. If freeWAIS-sf is compiled with -DPROXIMITY, word positions are returned otherwise character postitions.

In an scalar context the number of occurances of the word is returned.

       $headline = Wais::headline($database, $docid);

The function retrieves the headline (only the text!) of the document numbered $docid.

       $text = &Wais::document($database, $docid);

The function retrieves the text of the document numbered $docid.

       $apdu = Wais::generate_search_apdu($query,$database);
       $relevant = [$id1, 'TEXT', $id2, 'HTML'];
       $apdu = Wais::generate_search_apdu($query,$database,$relevant);

Document id's must be of type WAIS::Docid as returned by Wais::Result::header or Wais::Search::header. $WAIS::maxdoc may be set to modify the number of documents to retrieve.

       $apdu = Wais::generate_retrieval_apdu($database, $docid, $type);
       $apdu = Wais::generate_retrieval_apdu($database, $docid, 
                                             $type, $chunk);

Request to send the $chunk's chunk of the document whichs id is $docid (must be of type WAIS::Docid). $chunk defaults to 0. $Wais::CHARS_PER_PAGE may be set to influence the chunk size.

       $answer = Wais::local_answer($apdu);

Answer the request by local search/retrieval. The message header is stripped from the result for convenience (see the code of Wais::Search rsp. documentaion of Wais::Search::new below).

       $result = Wais::Search::new($message);

Turn the result message in an object of type Wais::Search. The following methods are available: diagnostics, header, and text. Result of the message is pretty the same as for Wais::Result. Just the tags are missing.

       $result = new Wais::Docid($distserver, $distdb, $distid,
                     $copyright,  $origserver, $origdb, $origid);

Only the first four arguments are manatory.

       ($distserver, $distdb, $distid, $copyright, $origserver, 
        $origdb, $origid) = Wais::Docid::split($result);
       ($distserver, $distdb, $distid) = Wais::Docid::split($result);
       ($distserver, $distdb, $distid) = $result->split;

The inverse of Wais::Docid::new

diagnostics

Return an array of references to [$code, $message]

header

Return an array of references to [$score, $lines, $length, $headline, $types, $docid].

text

Returns the chunk of the document requested. For documents larger than $Wais::CHARS_PER_PAGE more than one request must be send.

The objects will be destroyed by Perl.

$Wais::version

Generated by: sprintf(buf, "Wais %3.1f%d", VERSION, PATCHLEVEL);

$Wais:errmsg

Set to an verbose error message if something went wrong. Most functions return undef on failure after setting $Wais:errmsg.

$Wais::maxdoc

Maximum number of hits to return when searching. Defaults to 40.

$Wais::CHARS_PER_PAGE

Maximum number of bytes to retrieve in a single retrieve request. Wais:Retrieve sends multiple requests if necessary to retrieve a document. CHARS_PER_PAGE defaults to 4096.

$Wais::timeout

Number of seconds to wait for an answer from remote servers. Defaults to 120.

$Wais::maxnumfd

Maximum number of file descriptors to use simultaneously in Wais::Search. Defaults to 10.

Wais::Search currently splits the request in groups of $Wais::maxnumfd requests. Since some requests of the group might be local and/or some might refer to the same host/port, groups may not use all $Wais::maxnumfd possible file descriptors. Therefore some performance my be lost when more than $Wais::maxnumfd requests are processed.

Ulrich Pfeifer <pfeifer@ls6.cs.uni-dortmund.de>, Norbert Goevert <goevert@ls6.cs.uni-dortmund.de>