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| <h2>Decoder configuration parameters</h2> |
| </div> |
| |
| <div class="blog-post"> |
| |
| <p>Joshua configuration parameters affect the runtime behavior of the decoder itself. This page |
| describes the complete list of these parameters and describes how to invoke the decoder manually.</p> |
| |
| <p>To run the decoder, a convenience script is provided that loads the necessary Java libraries. |
| Assuming you have set the environment variable <code class="highlighter-rouge">$JOSHUA</code> to point to the root of your installation, |
| its syntax is:</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>$JOSHUA/bin/decoder [-m memory-amount] [-c config-file other-joshua-options ...] |
| </code></pre> |
| </div> |
| |
| <p>The <code class="highlighter-rouge">-m</code> argument, if present, must come first, and the memory specification is in Java format |
| (e.g., 400m, 4g, 50g). Most notably, the suffixes “m” and “g” are used for “megabytes” and |
| “gigabytes”, and there cannot be a space between the number and the unit. The value of this |
| argument is passed to Java itself in the invocation of the decoder, and the remaining options are |
| passed to Joshua. The <code class="highlighter-rouge">-c</code> parameter has special import because it specifies the location of the |
| configuration file.</p> |
| |
| <p>The Joshua decoder works by reading from STDIN and printing translations to STDOUT as they are |
| received, according to a number of <a href="#output">output options</a>. If no run-time parameters are |
| specified (e.g., no translation model), sentences are simply pushed through untranslated. Blank |
| lines are similarly pushed through as blank lines, so as to maintain parallelism with the input.</p> |
| |
| <p>Parameters can be provided to Joshua via a configuration file and from the command |
| line. Command-line arguments override values found in the configuration file. The format for |
| configuration file parameters is</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>parameter = value |
| </code></pre> |
| </div> |
| |
| <p>Command-line options are specified in the following format</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>-parameter value |
| </code></pre> |
| </div> |
| |
| <p>Values are one of four types (which we list here mostly to call attention to the boolean format):</p> |
| |
| <ul> |
| <li>STRING, an arbitrary string (no spaces)</li> |
| <li>FLOAT, a floating-point value</li> |
| <li>INT, an integer</li> |
| <li> |
| <p>BOOLEAN, a boolean value. For booleans, <code class="highlighter-rouge">true</code> evaluates to true, and all other values evaluate |
| to false. For command-line options, the value may be omitted, in which case it evaluates to |
| true. For example, the following are equivalent:</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>$JOSHUA/bin/decoder -mark-oovs true |
| $JOSHUA/bin/decoder -mark-oovs |
| </code></pre> |
| </div> |
| </li> |
| </ul> |
| |
| <h2 id="joshua-configuration-file">Joshua configuration file</h2> |
| |
| <p>In addition to the decoder parameters described below, the configuration file contains the model |
| feature weights. These weights are distinguished from runtime parameters in that they are delimited |
| by a space instead of an equals sign. They take the following |
| format, and by convention are placed at the end of the configuration file:</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>lm_0 4.23 |
| tm_pt_0 -0.2 |
| OOVPenalty -100 |
| </code></pre> |
| </div> |
| |
| <p>Joshua can make use of thousands of features, which are described in further detail in the |
| <a href="features.html">feature file</a>.</p> |
| |
| <h2 id="joshua-decoder-parameters">Joshua decoder parameters</h2> |
| |
| <p>This section contains a list of the Joshua run-time parameters. An important note about the |
| parameters is that they are collapsed to canonical form, in which dashes (-) and underscores (-) are |
| removed and case is converted to lowercase. For example, the following parameter forms are |
| equivalent (either in the configuration file or from the command line):</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code><span class="p">{</span><span class="err">top-n,</span><span class="w"> </span><span class="err">topN,</span><span class="w"> </span><span class="err">top_n,</span><span class="w"> </span><span class="err">TOP_N,</span><span class="w"> </span><span class="err">t-o-p-N</span><span class="p">}</span><span class="w"> |
| </span><span class="p">{</span><span class="err">poplimit,</span><span class="w"> </span><span class="err">pop-limit,</span><span class="w"> </span><span class="err">pop-limit,</span><span class="w"> </span><span class="err">popLimit,PoPlImIt</span><span class="p">}</span><span class="w"> |
| </span></code></pre> |
| </div> |
| |
| <p>This basically defines equivalence classes of parameters, and relieves you of the task of having to |
| remember the exact format of each parameter.</p> |
| |
| <p>In what follows, we group the configuration parameters in the following groups:</p> |
| |
| <ul> |
| <li><a href="#general">General options</a></li> |
| <li><a href="#pruning">Pruning</a></li> |
| <li><a href="#tm">Translation model options</a></li> |
| <li><a href="#lm">Language model options</a></li> |
| <li><a href="#output">Output options</a></li> |
| <li><a href="#modes">Alternate modes of operation</a></li> |
| </ul> |
| |
| <p><a id="general"></a></p> |
| |
| <h3 id="general-decoder-options">General decoder options</h3> |
| |
| <ul> |
| <li> |
| <p><code class="highlighter-rouge">c</code>, <code class="highlighter-rouge">config</code> — <em>NULL</em></p> |
| |
| <p>Specifies the configuration file from which Joshua options are loaded. This feature is unique in |
| that it must be specified from the command line (obviously).</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">amortize</code> — <em>true</em></p> |
| |
| <p>When true, specifies that sorting of the rule lists at each trie node in the grammar should be |
| delayed until the trie node is accessed. When false, all such nodes are sorted before decoding |
| even begins. Setting to true results in slower per-sentence decoding, but allows the decoder to |
| begin translating almost immediately (especially with large grammars).</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">server-port</code> — <em>0</em></p> |
| |
| <p>If set to a nonzero value, Joshua will start a multithreaded TCP/IP server on the specified |
| port. Clients can connect to it directly through programming APIs or command-line tools like |
| <code class="highlighter-rouge">telnet</code> or <code class="highlighter-rouge">nc</code>.</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>$ $JOSHUA/bin/decoder -m 30g -c /path/to/config/file -server-port 8723 |
| ... |
| $ cat input.txt | nc localhost 8723 > results.txt |
| </code></pre> |
| </div> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">maxlen</code> — <em>200</em></p> |
| |
| <p>Input sentences longer than this are truncated.</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">feature-function</code></p> |
| |
| <p>Enables a particular feature function. See the <a href="features.html">feature function page</a> for more information.</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">oracle-file</code> — <em>NULL</em></p> |
| |
| <p>The location of a set of oracle reference translations, parallel to the input. When present, |
| after producing the hypergraph by decoding the input sentence, the oracle is used to rescore the |
| translation forest with a BLEU approximation in order to extract the oracle-translation from the |
| forest. This is useful for obtaining an (approximation to an) upper bound on your translation |
| model under particular search settings.</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">default-nonterminal</code> — <em>“X”</em></p> |
| |
| <p>This is the nonterminal symbol assigned to out-of-vocabulary (OOV) items. Joshua assigns this |
| label to every word of the input, in fact, so that even known words can be translated as OOVs, if |
| the model prefers them. Usually, a very low weight on the <code class="highlighter-rouge">OOVPenalty</code> feature discourages their |
| use unless necessary.</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">goal-symbol</code> — <em>“GOAL”</em></p> |
| |
| <p>This is the symbol whose presence in the chart over the whole input span denotes a successful |
| parse (translation). It should match the LHS nonterminal in your glue grammar. Internally, |
| Joshua represents nonterminals enclosed in square brackets (e.g., “[GOAL]”), which you can |
| optionally supply in the configuration file.</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">true-oovs-only</code> — <em>false</em></p> |
| |
| <p>By default, Joshua creates an OOV entry for every word in the source sentence, regardless of |
| whether it is found in the grammar. This allows every word to be pushed through untranslated |
| (although potentially incurring a high cost based on the <code class="highlighter-rouge">OOVPenalty</code> feature). If this option is |
| set, then only true OOVs are entered into the chart as OOVs. To determine “true” OOVs, Joshua |
| examines the first level of the grammar trie for each word of the input (this isn’t a perfect |
| heuristic, since a word could be present only in deeper levels of the trie).</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">threads</code>, <code class="highlighter-rouge">num-parallel-decoders</code> — <em>1</em></p> |
| |
| <p>This determines how many simultaneous decoding threads to launch. </p> |
| |
| <p>Outputs are assembled in order and Joshua has to hold on to the complete target hypergraph until |
| it is ready to be processed for output, so too many simultaneous threads could result in lots of |
| memory usage if a long sentence results in many sentences being queued up. We have run Joshua |
| with as many as 64 threads without any problems of this kind, but it’s useful to keep in the back |
| of your mind.</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">weights-file</code> — NULL</p> |
| |
| <p>Weights are appended to the end of the Joshua configuration file, by convention. If you prefer to |
| put them in a separate file, you can do so, and point to the file with this parameter.</p> |
| </li> |
| </ul> |
| |
| <h3 id="pruning-options-a-idpruning-">Pruning options <a id="pruning"></a></h3> |
| |
| <ul> |
| <li> |
| <p><code class="highlighter-rouge">pop-limit</code> — <em>100</em></p> |
| |
| <p>The number of cube-pruning hypotheses that are popped from the candidates list for each span of |
| the input. Higher values result in a larger portion of the search space being explored at the |
| cost of an increased search time. For exhaustive search, set <code class="highlighter-rouge">pop-limit</code> to 0.</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">filter-grammar</code> — false</p> |
| |
| <p>Set to true, this enables dynamic sentence-level filtering. For each sentence, each grammar is |
| filtered at runtime down to rules that can be applied to the sentence under consideration. This |
| takes some time (which we haven’t thoroughly quantified), but can result in the removal of many |
| rules that are only partially applicable to the sentence.</p> |
| </li> |
| <li><code class="highlighter-rouge">constrain-parse</code> — <em>false</em></li> |
| <li> |
| <p><code class="highlighter-rouge">use_pos_labels</code> — <em>false</em></p> |
| |
| <p><em>These features are not documented.</em></p> |
| </li> |
| </ul> |
| |
| <h3 id="translation-model-options-a-idtm-">Translation model options <a id="tm"></a></h3> |
| |
| <p>Joshua supports any number of translation models. Conventionally, two are supplied: the main grammar |
| containing translation rules, and the glue grammar for patching things together. Internally, Joshua |
| doesn’t distinguish between the roles of these grammars; they are treated differently only in that |
| they typically have different span limits (the maximum input width they can be applied to).</p> |
| |
| <p>Grammars are instantiated with config file lines of the following form:</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>tm = TYPE OWNER SPAN_LIMIT FILE |
| </code></pre> |
| </div> |
| |
| <ul> |
| <li><code class="highlighter-rouge">TYPE</code> is the grammar type, which must be set to “thrax”. </li> |
| <li><code class="highlighter-rouge">OWNER</code> is the grammar’s owner, which defines the set of <a href="features.html">feature weights</a> that |
| apply to the weights found in each line of the grammar (using different owners allows each grammar |
| to have different sets and numbers of weights, while sharing owners allows weights to be shared |
| across grammars).</li> |
| <li><code class="highlighter-rouge">SPAN_LIMIT</code> is the maximum span of the input that rules from this grammar can be applied to. A |
| span limit of 0 means “no limit”, while a span limit of -1 means that rules from this grammar must |
| be anchored to the left side of the sentence (index 0).</li> |
| <li><code class="highlighter-rouge">FILE</code> is the path to the file containing the grammar. If the file is a directory, it is assumed |
| to be <a href="packed.html">packed</a>. Only one packed grammar can currently be used at a time.</li> |
| </ul> |
| |
| <p>For reference, the following two translation model lines are used by the <a href="pipeline.html">pipeline</a>:</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>tm = thrax pt 20 /path/to/packed/grammar |
| tm = thrax glue -1 /path/to/glue/grammar |
| </code></pre> |
| </div> |
| |
| <h3 id="language-model-options-a-idlm-">Language model options <a id="lm"></a></h3> |
| |
| <p>Joshua supports any number of language models. With Joshua 6.0, these |
| are just regular feature functions:</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>feature-function = LanguageModel -lm_file /path/to/lm/file -lm_order N -lm_type TYPE |
| feature-function = StateMinimizingLanguageModel -lm_file /path/to/lm/file -lm_order N -lm_type TYPE |
| </code></pre> |
| </div> |
| |
| <p><code class="highlighter-rouge">LanguageModel</code> is a generic language model, supporting types ‘kenlm’ |
| (the default) and ‘berkeleylm’. <code class="highlighter-rouge">StateMinimizingLanguageModel</code> |
| implements LM state minimization to reduce the size of context n-grams |
| where appropriate |
| (<a href="http://www.aclweb.org/anthology/W08-0402.pdf">Li and Khudanpur, 2008</a>; |
| <a href="https://aclweb.org/anthology/N/N13/N13-1116.pdf">Heafield et al., 2013</a>). This |
| is currently only supported by KenLM, so the <code class="highlighter-rouge">-lm_type</code> option is not |
| available here.</p> |
| |
| <p>The other key/value pairs are defined as follows:</p> |
| |
| <ul> |
| <li><code class="highlighter-rouge">lm_type</code>: one of “kenlm” “berkeleylm”</li> |
| <li><code class="highlighter-rouge">lm_order</code>: the order of the language model</li> |
| <li><code class="highlighter-rouge">lm_file</code>: the path to the language model file. All language model |
| types support the standard ARPA format. Additionally, if the LM |
| type is “kenlm”, this file can be compiled into KenLM’s compiled |
| format (using the program at <code class="highlighter-rouge">$JOSHUA/bin/build_binary</code>); if the |
| the LM type is “berkeleylm”, it can be compiled by following the |
| directions in |
| <code class="highlighter-rouge">$JOSHUA/src/joshua/decoder/ff/lm/berkeley_lm/README</code>. The |
| <a href="pipeline.html">pipeline</a> will automatically compile either type.</li> |
| </ul> |
| |
| <p>For each language model, you need to specify a feature weight in the following format:</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>lm_0 WEIGHT |
| lm_1 WEIGHT |
| ... |
| </code></pre> |
| </div> |
| |
| <p>where the indices correspond to the order of the language model declaration lines.</p> |
| |
| <h3 id="output-options-a-idoutput-">Output options <a id="output"></a></h3> |
| |
| <ul> |
| <li> |
| <p><code class="highlighter-rouge">output-format</code> <em>New in 5.0</em></p> |
| |
| <p>Joshua prints a lot of information to STDERR (making this more granular is on the TODO |
| list). Output to STDOUT is reserved for decoder translations, and is controlled by the</p> |
| |
| <ul> |
| <li> |
| <p><code class="highlighter-rouge">%i</code>: the sentence number (0-indexed)</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">%e</code>: the source sentence</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">%s</code>: the translated sentence</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">%S</code>: the translated sentence, with some basic capitalization and denomralization. e.g.,</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>$ echo "¿ who you lookin' at , mr. ?" | $JOSHUA/bin/decoder -output-format "%S" -mark-oovs false 2> /dev/null |
| ¿Who you lookin' at, Mr.? |
| </code></pre> |
| </div> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">%t</code>: the target-side tree projection, all printed on one line (PTB style)</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">%d</code>: the synchronous derivation, with each rules printed indented on their own lines</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">%f</code>: the list of feature values (as name=value pairs)</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">%c</code>: the model cost</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">%w</code>: the weight vector (unimplemented)</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">%a</code>: the alignments between source and target words (currently broken for hierarchical mode)</p> |
| </li> |
| </ul> |
| |
| <p>The default value is</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>output-format = %i ||| %s ||| %f ||| %c |
| </code></pre> |
| </div> |
| |
| <p>i.e.,</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>input ID ||| translation ||| model scores ||| score |
| </code></pre> |
| </div> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">top-n</code> — <em>300</em></p> |
| |
| <p>The number of translation hypotheses to output, sorted in decreasing order of model score</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">use-unique-nbest</code> — <em>true</em></p> |
| |
| <p>When constructing the n-best list for a sentence, skip hypotheses whose string has already been |
| output.</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">escape-trees</code> — <em>false</em></p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">include-align-index</code> — <em>false</em></p> |
| |
| <p>Output the source words indices that each target word aligns to.</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">mark-oovs</code> — <em>false</em></p> |
| |
| <p>if <code class="highlighter-rouge">true</code>, this causes the text “_OOV” to be appended to each untranslated word in the output.</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">visualize-hypergraph</code> — <em>false</em></p> |
| |
| <p>If set to true, a visualization of the hypergraph will be displayed, though you will have to |
| explicitly include the relevant jar files. See the example usage in |
| <code class="highlighter-rouge">$JOSHUA/examples/tree_visualizer/</code>, which contains a demonstration of a source sentence, |
| translation, and synchronous derivation.</p> |
| </li> |
| <li> |
| <p><code class="highlighter-rouge">dump-hypergraph</code> — “”</p> |
| |
| <p>This feature directs that the hypergraph should be written to disk for each input sentence. If |
| set, the value should contain the string “%d”, which is replaced with the sentence number. For |
| example,</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>cat input.txt | $JOSHUA/bin/decoder -dump-hypergraph hgs/%d.txt |
| </code></pre> |
| </div> |
| |
| <p>Note that the output directory must exist.</p> |
| |
| <p>TODO: revive the |
| <a href="http://aclweb.org/aclwiki/index.php?title=Hypergraph_Format">discussion on a common hypergraph format</a> |
| on the ACL Wiki and support that format.</p> |
| </li> |
| </ul> |
| |
| <h3 id="lattice-decoding">Lattice decoding</h3> |
| |
| <p>In addition to regular sentences, Joshua can decode weighted lattices encoded in |
| <a href="http://www.statmt.org/moses/?n=Moses.WordLattices">the PLF format</a>, except that path costs should |
| be listed as <b>log probabilities</b> instead of probabilities. Lattice decoding was originally |
| added by Lane Schwartz and <a href="http://www.cs.cmu.edu/~cdyer/">Chris Dyer</a>.</p> |
| |
| <p>Joshua will automatically detect whether the input sentence is a regular sentence (the usual case) |
| or a lattice. If a lattice, a feature will be activated that accumulates the cost of different |
| paths through the lattice. In this case, you need to ensure that a weight for this feature is |
| present in <a href="decoder.html">your model file</a>. The <a href="pipeline.html">pipeline</a> will handle this |
| automatically, or if you are doing this manually, you can add the line</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>SourcePath COST |
| </code></pre> |
| </div> |
| |
| <p>to your Joshua configuration file. </p> |
| |
| <p>Lattices must be listed one per line.</p> |
| |
| <h3 id="alternate-modes-of-operation-a-idmodes-">Alternate modes of operation <a id="modes"></a></h3> |
| |
| <p>In addition to decoding input sentences in the standard way, Joshua supports both <em>constrained |
| decoding</em> and <em>synchronous parsing</em>. In both settings, both the source and target sides are provided |
| as input, and the decoder finds a derivation between them.</p> |
| |
| <h4 id="constrained-decoding">Constrained decoding</h4> |
| |
| <p>To enable constrained decoding, simply append the desired target string as part of the input, in |
| the following format:</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code>source sentence ||| target sentence |
| </code></pre> |
| </div> |
| |
| <p>Joshua will translate the source sentence constrained to the target sentence. There are a few |
| caveats:</p> |
| |
| <ul> |
| <li> |
| <p>Left-state minimization cannot be enabled for the language model</p> |
| </li> |
| <li> |
| <p>A heuristic is used to constrain the derivation (the LM state must match against the |
| input). This is not a perfect heuristic, and sometimes results in analyses that are not |
| perfectly constrained to the input, but have extra words.</p> |
| </li> |
| </ul> |
| |
| <h4 id="synchronous-parsing">Synchronous parsing</h4> |
| |
| <p>Joshua supports synchronous parsing as a two-step sequence of monolingual parses, as described in |
| Dyer (NAACL 2010) (<a href="http://www.aclweb.org/anthology/N10-1033.pdf">PDF</a>). To enable this:</p> |
| |
| <ul> |
| <li> |
| <p>Set the configuration parameter <code class="highlighter-rouge">parse = true</code>.</p> |
| </li> |
| <li> |
| <p>Remove all language models from the input file </p> |
| </li> |
| <li> |
| <p>Provide input in the following format:</p> |
| |
| <div class="highlighter-rouge"><pre class="highlight"><code> source sentence ||| target sentence |
| </code></pre> |
| </div> |
| </li> |
| </ul> |
| |
| <p>You may also wish to display the synchronouse parse tree (<code class="highlighter-rouge">-output-format %t</code>) and the alignment |
| (<code class="highlighter-rouge">-show-align-index</code>).</p> |
| |
| |
| |
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