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5 Modules

GNU Dico comes with a set of loadable modules for handling various database formats and extending the server functionality. Modules are binary loadable files, installed in $prefix/lib/dico. They are configurable on per-module (see command) and per-database (see handler) basis.

In this chapter we will describe the modules included in the distribution of GNU Dico version 2.7.

5.1 Outline

The outline module supports databases written in Emacs outline mode. It is not designed for storing large amounts of data, its purpose rather is to handle small databases that can be composed easily and quickly using the Emacs editor.

The outline mode is described in Outline Mode in The Emacs Editor. In short, it is a usual plain text file, containing header lines and body lines. Header lines start with one or more stars, the number of starts indicating the nesting level of the heading in the document structure: one star for chapters, two stars for sections, etc. Body lines are anything that is not header lines.

The outline dictionary must have at least a chapter named ‘Dictionary’, which contains the dictionary corpus. Within it, each section is treated as a dictionary article, its header line giving the headword, and its body lines supplying the article itself. Apart from this, two more chapters have special meaning. The ‘Description’ chapter gives a short description to be displayed on SHOW DB command, and the ‘Info’ chapter supplies a full database description for SHOW INFO output. Both chapters are optional.

All three reserved chapter names are case-insensitive.

To summarize, the structure of an outline database is:

* Description
line
   
* Info
text

* Dictionary

** line
text

[any number of entries follows]

As an example of outline format, the GNU Dico package includes Ambrose Bierce’s Devil’s Dictionary in this format, see examples/devdict.out.

The initialization of the outline module does not require any command line parameters. To declare a database, supply its full file name to the database handler directive, as shown in the example below:

load-module outline;

database {
   name "devdict";
   handler "outline /var/db/devdict.out";
}

5.2 Dictorg

The dictorg module supports dictionaries in the format designed by DICT development group (http://dict.org). Lots of free dictionaries in this format are available from the FreeDict project.

A dictionary in this format consists of two files: a dictionary database file, named name.dict or name.dict.dz (a compressed form), and an index file, which lists article headwords with the corresponding offsets in the database. The index file is named name.index. The common part of these two file names, name, is called the base name for that dictionary.

An instance of the dictorg module is created using the following statement:

load-module inst-name {
    command "dictorg [options]";
}

where square brackets denote optional part. Valid options are the following:

dbdir=dir

Look for databases in directory dir.

show-dictorg-entries

Dictorg entries are special database entries that keep some service information, such as database description, etc. Such entries are marked with headwords that begin with ‘00-database-’. By default they are exempt from database look-ups and cannot be retrieved using MATCH or DEFINE command.

Using show-dictorg-entries removes this limitation.

sort

Sort the database index after loading. This option is designed for use with some databases that have malformed indexes. At the time of this writing the ‘eng-swa’ database from FreeDict requires this option.

Using sort may considerably slow down initial database loading.

trim-ws

Remove trailing whitespace from dictionary headwords at start up. This might be necessary for some databases.

The values set via these options become defaults for all databases using this module instance, unless overridden in their declarations.

A database that uses this module must be declared as follows:

database {
    handler "inst-name database=file [options]";
    ...
}

where inst-name is the instance name used in the load-module declaration above.

The database argument specifies the base name of the database. Unless file begins with a slash, the value of dbdir initialization option is prepended to it. If dbdir is not given and file does not begin with a slash, an error is signalled.

The options above are the same options as described in initialization procedure: show-dictorg-entries, sort, and trim-ws. If used, they override initialization settings for that particular database. Forms prefixed with ‘no’ can be used to disable the corresponding option for this database. For example, notrim-ws cancels the effect of trim-ws used when initializing the module instance.

5.3 Gcide

The gcide module provides support for GNU Collaborative International Dictionary of English. This dictionary can be downloaded from ftp://ftp.gnu.org/gnu/gcide. It consists of a set of files named from CIDE.A through CIDE.Z, written using a special markup. See http://gcide.gnu.org.ua, for a detailed information about the dictionary.

The gcide module is started via the following statement:

load-module gcide;

The database is initialized as follows:

database {
    handler "gcide dbdir=directory [options]";
    ...
}

The ‘dbdir’ parameter supplies the name of the directory where database files are located. Upon startup, the module scans the dictionary files and creates an index file, named GCIDE.IDX, if it does not already exist. The file is created using an ancillary program idxgcide, described below. Unless specified otherwise, this file is created in the same directory where the database files are located, therefore the directory must be writable for the user dicod is started as.

Other options are:

gcide parameter: idxdir directory

Specifies the directory where the CIDE.IDX index file resides or should reside.

gcide parameter: index-cache-size size

Sets the maximum number of index pages the module keeps in memory simultaneously. The default value is 16. The pages are cached using the last recently used algorithm. Raising this value will make dictionary accesses faster at the expense of using more memory.

gcide parameter: index-program progname

Specifies the full name of the index program. Usually this option is not needed, because the module is configured to start the idxgcide utility from its default location. It is mostly useful for the module developers.

gcide parameter: suppress-pr

This parameter suppresses the output of ‘pr’ (pronunciation) tags. According to GCIDE docs, very few of the pronunciation fields have been filled in, so it might be reasonable to avoid displaying them at all.

Starting from version 0.51, GCIDE contains the file INFO, which provides basic information about the dictionary. The gcide module returns contents of this file at the ‘SHOW INFO’ request. The first line of this file (with the trailing newline and final point removed) is returned as the short database description.

Here’s a full example of a ‘gcide’ as used in ‘dico.gnu.org.ua’:

load-module gcide;

database {
    name "gcide";
    handler "gcide dbdir=/var/dictdb/gcide-0.51 suppress-pr";
    languages-from "en";
    languages-to "en";
}

5.3.1 idxgcide

The idxgcide utility is used by the gcide module to index the GCIDE dictionary. You can start it manually to reindex the database. It can be needed, for example, if you install a modified version of the dictionary. The program is installed in libexecdir. The usage is:

idxgcide [options] dbdir [idxdir]

The only mandatory argument dbdir specifies the name of the directory where the GCIDE dictionary is installed. The optional idxdir argument specifies the directory for the index file, if it differs from dbdir. Available options are:

--debug
-d

Debug lexical analyzer.

--dry-run
-n

Do nothing, but print everything. This implies --verbose.

--verbose
-v

Increase output verbosity. This option can be specified multiple times, each occurrence increasing the verbosity level by one. By default the utility outputs only errors and warnings. At level one, it prints additionally the names of source files that are being indexed at the moment. At level two (the maximum level implemented at the moment) it outputs each headword being indexed along with its location. This is useful only for debugging.

--page-size=number
-p number

Defines the size of index file page. The number specifies the size in bytes. The following case-insensitive suffixes can be used: ‘k’ (‘kb’), ‘m’ (‘mb’) or ‘g’ (‘gb’), specifying kilobytes, megabytes and gigabytes (ouch!) correspondingly.

The default page size is 10240 bytes.

5.4 Wordnet

WordNet is a lexical database for the English language, created and maintained at the Cognitive Science Laboratory of Princeton University3. It groups English words into sets of synonyms called synsets, provides short, general definitions, and records the various semantic relations between these synonym sets.

Dico provides a wordnet module for reading WordNet lexical database files. The module relies on libWN, the support library distributed with the WordNet database.

There is a point worth noticing if you plan to use the WordNet library. Normally, the libWN is compiled as a static library with position-dependent code, which makes it difficult (or impossible, on 64-bit architectures) to use from the dynamically-loaded libraries, such as dicod modules. So, first of all you will need to rebuild WordNet so that it contains position-independent code. To do so, change to the WordNet source directory and reconfigure it as follows:

  ./configure CFLAGS=-fPIC [other_options]

where other_options stands for any other options you might wish to pass to configure.

If you are going to run this command in a source directory that has been previously configured, it is advisable to run ‘make distclean’ beforehand.

Debian-based systems provide a package ‘wordnet-dev’, which contains a properly built shared library. However, this library is named ‘libwordnet.so’, instead of the expected ‘libWN.so’. On such systems you will have to use the --with-libWN option to configure, in order to inform it about the change:

  ./configure --with-libWN=wordnet

Argument to this option is the new basename for the libWN library, without file suffix. Optionally, the ‘lib’ prefix is allowed,

The wordnet module is compiled automatically if the configure script was able to find the library and its header file wn.h. If it was not, use the --with-wordnet configure option to specify the location where these files can be found. For example, if WordNet was installed using the default procedure, then the following option will do the job:

  ./configure --with-wordnet=/usr/local/WordNet-3.0

This command tells Dico to look for WordNet library files in /usr/local/WordNet-3.0/lib and for include files in /usr/local/WordNet-3.0/include.

A compiled module is loaded using the following statement:

load-module wordnet {
    command "wordnet [parameters]";
}

Optional parameters are:

wordnet module parameter: wnhome dir

Base directory for WordNet files. This is the directory where WordNet was installed. For the wordnet module to work, it must contain the dict subdirectory with WordNet dictionary files.

If you installed WordNet to /usr/local/WordNet-3.0, so that running ls on that directory shows you:

$ ls /usr/local/WordNet-3.0/
bin/  dict/  doc/  include/  lib/  man/

then you would use

load-module wordnet {
    command "wordnet wnhome=/usr/local/WordNet-3.0";
}
wordnet module parameter: wnsearchdir dir

Directory in which the WordNet database has been installed.

Normally, these values are set at compile time and you won’t need to override them. The use of these parameters may, however, be necessary if the database was moved or installed in a non-standard location.

One or more WordNet database instances can be defined. They all will be sharing the same database. The reason for having several database instances is that they may have different output options. For example, you may configure one database to return word definitions and another one to act as a thesaurus.

Dico version 2.7 defines the following database parameters:

wordnet database parameter: pos value

Select part of speech to be displayed by this database. By default, all parts of speech are displayed. Valid values are:

all

Display all parts of speech. This is the default.

noun

Display only nouns.

verb

Display only verbs.

adj
adjective

Display only adjectives.

adv
adverb

Display only adverbs.

satellite
adjsat

Display only satellites.

wordnet database parameter: merge-defs

When specified, this parameter instructs the WordNet database to merge all definitions with the same part of speech into a single definition, which will be returned in the usual dictionary fashion, e.g.:

sail
n. 1. a large piece of fabric (usually canvas fabric) by
means of which wind is used to propel a sailing vessel 
Synonyms: {canvas}, {canvass}, {sheet}
2. an ocean trip taken for pleasure
Synonyms: {cruise}
3. any structure that resembles a sail
v. 1. traverse or travel on (a body of water); "We sailed
the Atlantic"; "He sailed the Pacific all alone" 
2. move with sweeping, effortless, gliding motions

By default, each definition is returned as a separate entry.

As an example, the following is the database definition the author uses on his server:

database {
    name "WordNet";
    handler "wordnet merge-defs";
    languages-from "en";
    languages-to "en";
    description "WordNet dictionary, version 3.0";
}

5.5 Guile

Guile is an acronym for GNU’s Ubiquitous Intelligent Language for Extensions. It provides a Scheme interpreter conforming to the R5RS language specification and a number of convenience functions. For information about the language, refer to Revised(5) Report on the Algorithmic Language Scheme. For a detailed description of Guile and its features, see Overview in The Guile Reference Manual.

The guile module provides an interface to Guile that allows for writing GNU Dico modules in Scheme. The module is loaded using the following configuration file statement:

load-module mod-name {
   command "guile [options]"
           " init-script=script"
           " init-args=args"
           " init-fun=function";
}

The init-script parameter specifies the name of a Scheme source file to be loaded in order to initialize the module. The init-args parameter supplies additional arguments to the module. They will be accessible to the script via command-line function. This parameter is optional.

The init-fun parameter specifies the name of a function that will be invoked to perform initialization of the module and of particular databases. See Guile Initialization, for a description of initialization sequence. Optional arguments, options, are:

debug

Enable Guile debugging and stack traces.

nodebug

Disable Guile debugging and stack traces (default).

load-path=path

Append directories from path to the list of directories which should be searched for Scheme modules and libraries. The path must be a list of directory names, separated by colons.

This option modifies the value of Guile’s %load-path variable. See the section Configuration and Installation in the Guile Reference Manual.

Guile databases are declared using the following syntax:

database {
        name "dbname";
        handler "mod-name [options] cmdline";
}

where:

dbname

gives the name for this database,

mod-name

the name given to Guile module in load-module statement (see above),

options

options that override global settings given in the load-module statement. The following options are understood: init-script, init-args, and init-fun. Their meaning is the same as for load-module statement (see above), except that they affect only this particular database.

cmdline

the command line that will be passed to the Guile open-db callback function (see open-db).

5.5.1 Virtual Functions

A database handled by the guile module is assigned a virtual function table. This table is an association list which keeps Scheme call-back functions implemented to perform particular tasks on that database. In this list, the car of each element contains the name of a function, and its cdr gives the corresponding function. The defined function names and their semantics are:

open

Open the database.

close

Close the database.

descr

Return a short description of the database.

info

Return a full information about the database.

define

Define a word.

match

Look up a word in the database.

output

Output a search result.

result-count

Return number of entries in the result.

For example, the following is a valid virtual function table:

(list (cons "open" open-module)
      (cons "close" close-module)
      (cons "descr" descr)
      (cons "info" info)
      (cons "define" define-word)
      (cons "match" match-word)
      (cons "output" output)
      (cons "result-count" result-count))

Apart from a per-database virtual table, there is also a global virtual function table, which supplies entries missing in the former. Both tables are created during the module initialization, as described in the next subsection.

The purposes of particular virtuals functions are described in Guile API.

5.5.2 Guile Initialization

The following configuration statement causes loading and initialization of the guile module:

load-module mod-name {
   command "guile init-script=script"
           " init-fun=function";
}

Upon module initialization stage, the module attempts to load the file named script. The file is loaded using primitive-load call (see Loading in The Guile Reference Manual), i.e. the load paths are not searched, so script must be an absolute path name. The init-fun parameter supplies the name of the initialization function. This Scheme function constructs virtual function tables for the module itself and for each database that uses this module. It must be declared as follows:

(define (function arg)
  ...)

This function is called several times. First of all, it is called after the script is loaded. This time it is given #f as its argument, and its return value is saved as a global function table. Then, it is called for each database statement that has mod-name (used in load-module above) in its handler keyword, e.g.:

database {
   name db-name;
   handler "mod-name …";
}

This time, it is given db-name as its argument and the value it returns is stored as the virtual function table for this particular database.

The following example function returns a complete virtual function table:

(define-public (my-dico-init arg)
  (list (cons "open" open-module)
        (cons "close" close-module)
        (cons "descr" descr)
        (cons "info" info)
        (cons "lang" lang)
        (cons "define" define-word)
        (cons "match" match-word)
        (cons "output" output)
        (cons "result-count" result-count)))

5.5.3 Guile API

This subsection describes callback functions that a Guile database module must provide. Each description begins with the function prototype and its entry in the virtual function table.

Callback functions can be subdivided into two groups: database functions and search functions.

Database callback functions are responsible for opening and closing databases and for returning information about them.

Guile Callback: open-db name . args

Virtual table: (cons "open" open-db)

Open the database. The argument name contains database name as given in the name statement of the corresponding database block (see Databases). Optional argument args is a list of command line parameters obtained from cmdline in handler statement (see guile-cmdline). For example, if the configuration file contained:

database {
    name "foo";
    handler "guile db=file 1 no";
}

then the open-db callback will be called as:

(open-db "foo" '("db=file" "1" "no"))

The open-db callback returns a database handle, i.e. an opaque object that will subsequently be used to identify this database. This value, hereinafter named dbh, will be passed to another callback functions that need to access the database.

The return value #f or '() indicates an error.

Guile Callback: close-db dbh

Virtual Table: (cons "close" close-db)

Close the database. This function is called during the cleanup procedure, before termination of dicod. The argument dbh is a database handle returned by open-db.

The return value from close-db is ignored. To communicate errors to the daemon, throw an exception.

Guile Callback: descr dbh

Virtual Table: (cons "descr" descr)

Return a short textual description of the database, for use in SHOW DB output. If there is no description, returns #f or '().

The argument dbh is a database handle returned by open-db.

This callback is optional. If it is not defined, or if it returns #f ('()), the text from description statement is used (see description). Otherwise, if no description statement is present, an empty string will be returned.

Guile Callback: info dbh

Virtual Table: (cons "info" info)

Return a verbose, eventually multi-line, textual description of the database, for use in SHOW INFO output. If there is no description, returns #f or '().

The argument dbh is a database handle returned by open-db.

This callback is optional. If it is not defined, or if it returns #f ('()), the text from info statement is used (see info). If there is no info statement, the string ‘No information available’ is used.

Guile Callback: lang dbh

Virtual Table: (cons "lang" lang)

Return a cons of languages supported by this database: Its car is a list of source languages, and its cdr is a list of destination languages. For example, the following return value indicates that the database contains translations from English to French and Spanish:

 (cons (list "en") (list "fr" "es"))

A database is searched in a two-phase process. First, an appropriate callback is called to do the search: define-word is called for DEFINE searches and match-word is called for matches. This callback returns an opaque entity, called result handle, which is then passed to the output callback, which is responsible for outputting it.

Guile Callback: define-word dbh word

Virtual Table: (cons "define" define-word)

Find definitions of word word in the database dbh. Return a result handle. If nothing is found, return #f or '().

The argument dbh is the database handle returned by open-db.

Guile Callback: match-word dbh strat key

Virtual Table: (cons "match" match-word)

Find in the database dbh all headwords that match key, using strategy strat. Return a result handle. If nothing is found, return #f or '().

The key is a Dico Key object, which contains information about the word being looked for. To obtain the actual word, use the dico-key->word function (see dico-key->word).

The argument dbh is a database handle returned by open-db. The matching strategy strat is a special Scheme object that can be accessed using a set of functions described below (see Dico Scheme Primitives).

Guile Callback: result-count resh

Virtual Table: (cons "result-count" result-count)

Return the number of elements in the result set resh.

Guile Callback: output resh n

Virtual Table: (cons "output" output)

Output nth result from the result set resh. The argument resh is a result handle returned by define-word or match-word callback.

The data must be output to the current output port, e.g. using display or format primitives. If resh represents a match result, the output must not be quoted or terminated by newlines.

It is guaranteed that the output callback will be called as many times as there are elements in resh (as determined by the result-count callback) and that for each subsequent call the value of n equals its value from the previous call incremented by one.

At the first call n equals 0.

5.5.4 Dico Scheme Primitives

GNU Dico provides the following Scheme primitives for accessing various fields of the strat and key arguments to match callback:

Function: dico-key? obj

Return ‘#t’ if obj is a Dico key object.

Function: dico-key->word key

Extract the lookup word from the key object key.

Function: dico-make-key strat word

Create new key object from strategy strat and word word.

Function: dico-strat-selector? strat

Return true if strat has a selector (see Selector).

Function: dico-strat-select? strat word key

Return true if key matches word as per strategy selector strat. The key is a ‘Dico Key’ object.

Function: dico-strat-name strat

Return the name of strategy strat.

Function: dico-strat-description strat

Return a textual description of the strategy strat.

Function: dico-strat-default? strat

Return true if strat is a default strategy. See default strategy.

Function: dico-register-strat strat descr [fun]

Register a new strategy. If fun is given it will be used as a callback for that strategy. Notice, that you can use strategies implemented in Guile in your C code as well (see strategy).

The selector function must be declared as follows:

(define (fun key word)
  ...)

It must return #t if key matches word, and #f otherwise.

5.5.5 Example Module

In this subsection we will show how to build a simple dicod module written in Scheme. The source code of this module, called listdict.scm and a short database for it, numerals-pl.db, are shipped with the distribution in the directory examples.

The database is stored in a disk file in form of a list. The first two elements of this list contain database description and full information strings. Rest of elements are conses, whose car contains the headword, and cdr contains the corresponding dictionary article. Following is an example of such a database:

("Short English-Norwegian numerals dictionary"
 "Short English-Norwegian dictionary of numerals (1 - 7)"
 ("one" . "en")
 ("two" . "to")
 ("three" . "tre")
 ("four" . "fire")
 ("five" . "fem")
 ("six" . "seks")
 ("seven" . "sju"))

We wish to declare such databases in dicod.conf the following way:

database {
        name "numerals";
        handler "guile example.db";
}

Thus, the rest argument to ‘open-db’ callback will be ‘("guile" "example.db")’ (see open-db). Given this, we may write the callback as follows:

(define (open-db name . rest)
  (let ((db (with-input-from-file
                (cadr rest)
              (lambda () (read)))))
    (cond
     ((list? db) (cons name db))
     (else
      (format (current-error-port) "open-module: ~A: invalid format\n"
              (car args))
      #f))))

The list returned by this callback will then be passed as a database handle to another callback functions. To facilitate access to particular elements of this list, it is convenient to define the following syntax:

(define-syntax db:get
  (syntax-rules (info descr name corpus)
    ((db:get dbh name)   ;; Return the name of the database.
     (list-ref dbh 0))
    ((db:get dbh descr)  ;; Return the desctiption.
     (list-ref dbh 1))
    ((db:get dbh info)   ;; Return the info string. 
     (list-ref dbh 2))
    ((db:get dbh corpus) ;; Return the word list.
     (list-tail dbh 3))))

Now, we can write ‘descr’ and ‘info’ callbacks:

(define (descr dbh)
  (db:get dbh descr))

(define (info dbh)
  (db:get dbh info))

The two callbacks ‘define-word’ and ‘match-word’ provide the core module functionality. Their results will be passed to ‘output’ and ‘result-count’ callbacks as a “result handler” argument. In the spirit of Scheme, we make the result a list. Its car is a boolean value: #t, if the result comes from ‘define-word’ callback, and #f if it comes from ‘match-word’. The cdr of this list contains a list of matches. For ‘define-word’, it is a list of conses copied from the database word list, whereas for ‘match-word’, it is a list of headwords.

The ‘define-word’ callback returns all list entries whose cars contain the look up word. It uses mapcan function, which is supposed to be defined elsewhere:

(define (define-word dbh word)
  (let ((res (mapcan (lambda (elt)
                       (and (string-ci=? word (car elt))
                            elt))
                     (db:get dbh corpus))))
    (and res (cons #t res))))

The ‘match-word’ callback (see match-word) takes three arguments: a database handler dbh, a strategy descriptor strat, and a word word to look for. The result handle it returns contains a list of headwords from the database that match word in the sense of strat. Thus, the behavior of ‘match-word’ depends on the strat. To implement this, let’s define a list of directly supported strategies (see below for definitions of particular ‘match-’ functions):

(define strategy-list
  (list (cons "exact"  match-exact)
        (cons "prefix"  match-prefix)
        (cons "suffix"  match-suffix)))

The ‘match-word’ callback will then select an entry from that list and call its cdr, e.g.:

(define (match-word dbh strat key)
  (let ((sp (assoc (dico-strat-name strat) strategy-list)))
    (let ((res (cond
                (sp
                 ((cdr sp) dbh strat (dico-key->word key)))

If the requested strategy is not in that list, the function will use the selector function if it is available, and the default matching function otherwise:

                ((dico-strat-selector? strat)
                 (match-selector dbh strat key))
                (else
                 (match-default dbh strat (dico-key->word key))))))

Notice the use of dico-key->word function to extract the actual lookup word from the key object.

To summarize, the ‘match-word’ callback is:

(define (match-word dbh strat key)
  (let ((sp (assoc (dico-strat-name strat) strategy-list)))
    (let ((res (cond
                (sp
                 ((cdr sp) dbh strat (dico-key->word key)))
                ((dico-strat-selector? strat)
                 (match-selector dbh strat key))
                (else
                 (match-default dbh strat (dico-key->word key))))))
      (if res
          (cons #f res)
          #f))))

Now, let’s create the ‘match-’ functions it uses. The ‘exact’ strategy is easy to implement:

(define (match-exact dbh strat word)
  (mapcan (lambda (elt)
            (and (string-ci=? word (car elt))
                 (car elt)))
          (db:get dbh corpus)))

The ‘prefix’ and ‘suffix’ strategies are implemented using SRFI-13 (see SRFI-13 in The Guile Reference Manual) functions string-prefix-ci? and string-suffix-ci?, e.g.:

(define (match-prefix dbh strat word)
  (mapcan (lambda (elt)
            (and (string-prefix-ci? word (car elt))
                 (car elt)))
          (db:get dbh corpus)))

Notice that whereas the ‘prefix’ strategy is defined by the server itself, the ‘suffix’ strategy is an extension, and should therefore be registered:

(dico-register-strat "suffix" "Match word suffixes")

The match-selector function is pretty similar to its siblings, except that it uses dico-strat-select? (see dico-strat-select?) to select the matching elements. This also leads to this function expecting a key as its third argument, in contrast to the previous matchers, which expect the actual lookup word there:

(define (match-selector dbh strat key)
  (mapcan (lambda (elt)
            (and (dico-strat-select? strat (car elt) key)
                 (car elt)))
          (db:get dbh corpus)))

Finally, the match-default is a variable that refers to the default matching strategy for this module, e.g.:

(define match-default match-prefix)

The two callbacks left to define are ‘result-count’ and ‘output’. The first of them simply returns the number of elements in cdr of the result:

(define (result-count rh)
  (length (cdr rh)))

The behavior of ‘output’ depends on whether the result is produced by ‘define-word’ or by ‘match-word’.

(define (output rh n)
  (if (car rh)
      ;; Result comes from DEFINE command.
      (let ((res (list-ref (cdr rh) n)))
        (display (car res))
        (newline)
        (display (cdr res)))
      ;; Result comes from MATCH command.
      (display (list-ref (cdr rh) n))))

Finally, at the end of the module the callbacks are made known to dicod by the module initialization function:

(define-public (example-init arg)
  (list (cons "open" open-module)
        (cons "descr" descr)
        (cons "info" info)
        (cons "define" define-word)
        (cons "match" match-word)
        (cons "output" output)
        (cons "result-count" result-count)))

Notice, that in this implementation ‘close-db’ callback was not needed.

5.6 Python

The python module provides an interface which allows programmers to write loadable modules in Python. The syntax for loading the module is:

load-module name {
  command "python"
          " init-script=name"
          " load-path=path"
          " root-class=name";
}

All parameters are optional:

python module: load-path=path

Augments the default search path for Python modules. The format of path is the usual UNIX path specification: a colon-separated list of directory names.

python module: init-script=name

Specifies the name of the initial Python source file. This file will be loaded and interpreted immediately after loading the module.

python module: root-class=name

Sets the name of the Python root class, which is responsible for the dictionary operations.

A particular instance of the python module is loaded using the handler statement within a database block. This statement takes the same parameters as described above, plus any number of command line arguments, which will be passed to the root class constructor.

5.6.1 Python Dictionary Class

The dictionary class must define the following methods:

Method on DictionaryClass: __init__ self *argv

Class constructor. The argv array supplies positional arguments from the handler statement in the configuration file.

Method on DictionaryClass: open self dbname

Opens the database named dbname. Returns ‘True’ on success and ‘False’ on failure.

Method on DictionaryClass: close self

Closes the database.

Method on DictionaryClass: descr self

Returns a short description of the database.

Method on DictionaryClass: info self

Returns a text describing the database.

Method on DictionaryClass: lang self

Optional. Returns supported languages as ‘(src, dst)’.

Method on DictionaryClass: define_word self word

Defines word. Returns a result (an opaque Python object) if the definition was found or ‘False’ otherwise.

Method on DictionaryClass: match_word self strat word

Searches for word in the database using strategy strat. Returns a result (an opaque Python object) if some matches were found or ‘False’ otherwise.

Method on DictionaryClass: output self result n

Outputs nth result from the result set result.

Method on DictionaryClass: result_count self result

Returns number of elements in the result set.

Method on DictionaryClass: compare_count self result

Optional. Returns the number of comparisons performed when constructing the result set.

Method on DictionaryClass: result_headers self result hdr

Optional. Returns a dictionary of MIME headers.

Method on DictionaryClass: free_result self result

Reclaims any resources used by the result set.

5.6.2 Dico Python Primitives

Python primitive: register_strat name descr [proc]

Registers new match strategy. The arguments are:

name

Strategy name for use in the MATCH command.

descr

The dscription, which will appear in the output of SHOW STRAT command.

proc

Optional selector procedure.

If the proc argument is present, it must be the name of a Python function declared as:

def select(opcode key headword):

Its arguments are:

opcode

Integer operation code.

key

An DicoSelectionKey object identifying the search term (see DicoSelectionKey).

headword

The headword being examined.

At the beginning of the search, the function is called with the ‘DICO_SELECT_BEGIN’ as its opcode argument. It must perform the necessary initialization and return.

At the end of the search loop, the function is called with opcodeDICO_SELECT_END’. It must perform the necessary deinitialization procedures and exit.

In both cases, the key and headword arguments are not defined.

Within the search loop, the function will be called for each headword from the database. The opcode parameter will be ‘DICO_SELECT_RUN’. In this case the function must return ‘True’ if the headword matches the key and ‘False’ otherwise.

Python primitive: register_markup name

Registers a markup name.

Python primitive: current_markup

Returns the name of the current markup.

5.6.2.1 The DicoSelectionKey class

The DicoSelectionKey class represents a search key and is used when looking for matches. Calling str on the object of that class returns the search term itself, as does the word method:

Method on DicoSelectionKey: word

Returns the search term. It is equivalent to the __str__ attribute.

5.6.2.2 The DicoStrategy class

A match strategy is represented by an object of the DicoStrategy class.

Variable of DicoStrategy: name

The name of that strategy.

Variable of DicoStrategy: descr

Textual description of the strategy.

Variable of DicoStrategy: has_selector

True’ if this strategy has a selector (see Python Selector).

Variable of DicoStrategy: name is_default

True’ if this is the default strategy.

Method on DicoStrategy: select headword key

Returns ‘True’ if key matches headword as per this strategy.

5.6.3 Python Example

In this subsection we will show a simple database module written in Python. This module handles simple textual databases in the following format:

Now, let’s create a module for handling this format. First, we need to import Dico primitives (see Dico Python Primitives) and the ‘sys’ module. The latter is needed for output functions:

import dico
import sys

Then, a result class will be needed for match_word and define_word methods. It will contain the actual data in the variable ‘result’:

class DicoResult:
    # actual data.
    result = {}
    # number of comparisons.
    compcount = 0
    
    def __init__ (self, *argv):
        self.result = argv[0]
        if len (argv) == 2:
             self.compcount = argv[1]

    def count (self):
        return len (self.result)

    def output (self, n):
        pass

    def append (self, elt):
        self.result.append (elt)

The following two classes extend ‘DicoResult’ for use with ‘DEFINE’ and ‘MATCH’ operations. The define_word method will return an instance of the ‘DicoDefineResult’ class:

class DicoDefineResult (DicoResult):
    def output (self, n):
        print "%d. %s" % (n + 1, self.result[n])
        print "---------",

The match_word method will return an instance of the ‘MatchResult’ class:

class DicoMatchResult (DicoResult):
    def output (self, n):
        sys.stdout.softspace = 0
        print self.result[n],

Now, let’s define the dictionary class:

class DicoModule:
    # The dictionary converted to associative array.
    adict =  {}
    # The database name.
    dbname = ''
    # The name of the corresponding disk file.
    filename = ''
    # A sort information about the database.
    mod_descr = ''
    # A verbose description of the database is kept.
    # as an array of strings.
    mod_info = []
    # A list of source and destination languages:
    langlist = ()

The class constructor takes a single argument, defining the name of the database file:

    def __init__ (self, *argv):
        self.filename = argv[0]
        pass

The ‘open’ method opens the database and reads its data:

    def open (self, dbname):
        self.dbname = dbname
        file = open (self.filename, "r")
        for line in file:
            if line.startswith ('--'):
                continue
            if line.startswith ('descr: '):
                self.mod_descr = line[7:].strip (' \n')
                continue
            if line.startswith ('info: '):
                self.mod_info.append (line[6:].strip (' \n'))
                continue
            if line.startswith ('lang: '):
                s = line[6:].strip (' \n').split(':', 2)
                if (len(s) == 1):
                    self.langlist = (s[0].split (), \
                                     s[0].split ())
                else:
                    self.langlist = (s[0].split (), \
                                     s[1].split ())
                continue
            f = line.strip (' \n').split (' ', 1)
            if len (f) == 2:
                self.adict[f[0].lower()] = f[1].strip (' ')
        file.close()
        return True

The database is kept entirely in memory, so there is no need for ‘close’ method. However, it must be declared anyway:

    def close (self):
        return True

The methods returning database information are trivial:

    def descr (self):
        return self.mod_descr

    def info (self):
        return '\n'.join (self.mod_info)
    
    def lang (self):
        return self.langlist

The ‘define_word’ method checks if the search term is present in the dictionary, and, if so, converts it to the DicoDefineResult:

    def define_word (self, word):
        if self.adict.has_key (word):
            return DicoDefineResult ([self.adict[word]])
        return False

The ‘match_word’ method supports the ‘exact’ strategy natively via the has_key attribute of adict:

    def match_word (self, strat, key):
        if strat.name == "exact":
            if self.adict.has_key (key.word.lower ()):
                return DicoMatchResult \
                        ([self.adict[key.word.lower()]])

Other strategies are supported as long as they have selectors:

        elif strat.has_selector:
            res = DicoMatchResult ([], len (self.adict))
            for k in self.adict:
                if strat.select (k, key):
                    res.append (k)
            if res.count > 0:
                return res
        return False

The rest of methods rely on the result object to do the right thing:

    def output (self, rh, n):
        rh.output (n)
        return True

    def result_count (self, rh):
        return rh.count ()

    def compare_count (self, rh):
        return rh.compcount

5.7 Stratall

The stratall module provides a new strategy, called ‘all’. This strategy always returns a full list of headwords from the database, no matter what the actual search word is.

To load this strategy, use the following configuration statement:

load-module stratall;

Using this strategy on a full set of databases (‘MATCH * all ""’) produces enormous amount of output, which may induce a considerable strain on the server, therefore it is advised to block such usage as suggested in Strategies and Default Searches:

strategy all {
        deny-all yes;
}

5.8 Substr

The substr module provides a ‘substr’ search strategy. This strategy matches a substring anywhere in the keyword. For example:

C: MATCH eng-deu substr orma
S: 152 207 matches found: list follows
S: eng-deu "abnormal"
S: eng-deu "conformable"
S: eng-deu "doorman"
S: eng-deu "format"
…

The loading procedure expects no arguments:

load-module substr;

5.9 Word

The word module provides the following strategies:

word

Match separate words within headwords.

first

Match the first word within headwords.

last

Match the last word within headwords.

The initialization procedure loads all three if given no arguments, as in

load-module word;

If arguments are given, the initialization procedure loads only those strategies that are listed in its command line. For example, the statement below loads only ‘first’ and ‘last’ strategies:

load-module word {
   command "word first last";
}   

The following is an example of using one of those strategies in a dico session:

C: MATCH devdict word government
S: 152 1 matches found: list follows
S: devdict "MONARCHICAL GOVERNMENT"
S: .
S: 250 Command complete

5.10 Nprefix

The nprefix module provides a strategy similar to ‘prefix’, but which returns the specified range of bytes. For example, the statement

MATCH dict nprefix skip#count#string

where skip and count are positive integer numbers, returns at most count headwords whose prefix matches string, omitting first skip unique matches.

The entire ‘skip#count#’ construct is optional. If not supplied, the ‘nprefix’ strategy behaves exactly as ‘prefix’.

The module is loaded using this simple statement:

load-module nprefix;

5.11 metaphone2

The metaphone2 module provides a strategy based on Double Metaphone phonetic encoding algorithm, published by Lawrence Philips.

The module is normally loaded as follows:

load-module metaphone2;

The only available initialization parameter is

metaphone2 parameter: size number

Defines the size of computed Double Metaphone codes, in characters. The default is 4.

load-module metaphone2 {
   command "metaphone2 size=16";
}

5.12 Pcre

The pcre module provides a matching strategy using Perl-compatible regular expressions. The module is loaded using a simple statement:

load-module pcre;

The strategy has the same name as the module and is reflected in the server’s HELP output as shown below:

pcre  "Match using Perl-compatible regular expressions"

The headword argument to the pcre MATCH statement should be a valid Perl regular expression. It can optionally be enclosed in a pair of slashes, in which case one or more of the following flags can appear after the closing slash:

a

The regexp is anchored, that is, it is constrained to match only at the first matching point in the string that is being searched.

e

Ignore whitespace and ‘#’ comments in the expression.

i

Ignore case when matching.

G

Inverts the greediness of the quantifiers so that they are not greedy by default, but become greedy if followed by ‘?’. The same can also be achieved by setting the ‘(?U)’ option within the pattern.

Any of these flags can also be used in reverted case, which also reverts its meaning. For example, ‘I’ means case-sensitive matching.

Here is an example of using this strategy in a dico session:

MATCH ! pcre "/\\stext/i"

5.13 Ldap

The ldap module loads the support for LDAP user databases. It is available if Dico has been configured with LDAP.

The module needs no additional configuration parameters:

load-module ldap;

See ldap userdb, for a description of its use.

5.14 pam

The pam module implements user authentication via PAM. It can be used only with ‘LOGIN’ and ‘PLAIN’ GSASL authentication methods.

The module is loaded as follows:

load-module pam {
    command "pam [service=sname]";
}

where sname is the name of PAM service to use. If not supplied, ‘dicod’ service will be used.

The user database is normally initialized as:

user-db "pam://localhost";

If password-resource statement is given, its value will be used as service name, instead of the one specified in the load-module statement, e.g.:

user-db "pam://localhost" {
    password-resource "local";
}    

The group-resource statement is not used, because there is no mechanism to return textual data from PAM.

Footnotes

(3)

See http://wordnet.princeton.edu/wordnet/, for a detailed information, including links to download.

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