repo_zf1/documentation/manual/en/module_specs/Zend_Search_Lucene-Searching.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- Reviewed: no -->
<sect1 id="zend.search.lucene.searching">
    <title>Searching an Index</title>

    <sect2 id="zend.search.lucene.searching.query_building">
        <title>Building Queries</title>

        <para>
            There are two ways to search the index. The first method uses
            query parser to construct a query from a string. The second is
            to programmatically create your own queries through the
            <classname>Zend_Search_Lucene</classname> <acronym>API</acronym>.
        </para>

        <para>
        Before choosing to use the provided query parser, please consider
        the following:

            <orderedlist>
                <listitem>
                    <para>
                        If you are programmatically creating a query string and then parsing
                        it with the query parser then you should consider building your queries
                        directly with the query <acronym>API</acronym>. Generally speaking, the
                        query parser is designed for human-entered text, not for program-generated
                        text.
                    </para>
                </listitem>

                <listitem>
                    <para>
                        Untokenized fields are best added directly to queries and not through
                        the query parser. If a field's values are generated programmatically
                        by the application, then the query clauses for this field should also
                        be constructed programmatically.
                        An analyzer, which the query parser uses, is designed to convert
                        human-entered text to terms. Program-generated values, like dates,
                        keywords, etc., should be added with the query <acronym>API</acronym>.
                    </para>
                </listitem>

                <listitem>
                    <para>
                        In a query form, fields that are general text should use the query parser.
                        All others, such as date ranges, keywords, etc., are better added directly
                        through the query <acronym>API</acronym>. A field with a limited set of
                        values that can be specified with a pull-down menu should not be added to a
                        query string that is subsequently parsed but instead should be added as a
                        TermQuery clause.
                    </para>
                </listitem>

                <listitem>
                    <para>
                        Boolean queries allow the programmer to logically combine two or more
                        queries into new one. Thus it's the best way to add additional criteria to a
                        search defined by a query string.
                    </para>
                </listitem>
            </orderedlist>
        </para>

        <para>
            Both ways use the same <acronym>API</acronym> method to search through the index:
        </para>

        <programlisting language="php"><![CDATA[
$index = Zend_Search_Lucene::open('/data/my_index');

$index->find($query);
]]></programlisting>

        <para>
            The <methodname>Zend_Search_Lucene::find()</methodname> method determines the input type
            automatically and uses the query parser to construct an appropriate
            <classname>Zend_Search_Lucene_Search_Query</classname> object from an input of type
            string.
        </para>

        <para>
            It is important to note that the query parser uses the standard analyzer to tokenize
            separate parts of query string. Thus all transformations which are applied to indexed
            text are also applied to query strings.
        </para>

        <para>
            The standard analyzer may transform the query string to lower case for
            case-insensitivity, remove stop-words, and stem among other transformations.
        </para>

        <para>
            The <acronym>API</acronym> method doesn't transform or filter input terms in any way.
            It's therefore more suitable for computer generated or untokenized fields.
        </para>

        <sect3 id="zend.search.lucene.searching.query_building.parsing">
            <title>Query Parsing</title>

            <para>
                <methodname>Zend_Search_Lucene_Search_QueryParser::parse()</methodname> method may
                be used to parse query strings into query objects.
            </para>

            <para>
                This query object may be used in query construction <acronym>API</acronym> methods
                to combine user entered queries with programmatically generated queries.
            </para>

            <para>
                Actually, in some cases it's the only way to search for values within untokenized
                fields:

                <programlisting language="php"><![CDATA[
$userQuery = Zend_Search_Lucene_Search_QueryParser::parse($queryStr);

$pathTerm  = new Zend_Search_Lucene_Index_Term(
                     '/data/doc_dir/' . $filename, 'path'
                 );
$pathQuery = new Zend_Search_Lucene_Search_Query_Term($pathTerm);

$query = new Zend_Search_Lucene_Search_Query_Boolean();
$query->addSubquery($userQuery, true /* required */);
$query->addSubquery($pathQuery, true /* required */);

$hits = $index->find($query);
]]></programlisting>
            </para>

            <para>
                <methodname>Zend_Search_Lucene_Search_QueryParser::parse()</methodname> method also
                takes an optional encoding parameter, which can specify query string encoding:

                <programlisting language="php"><![CDATA[
$userQuery = Zend_Search_Lucene_Search_QueryParser::parse($queryStr,
                                                          'iso-8859-5');
]]></programlisting>
            </para>

            <para>
                If the encoding parameter is omitted, then current locale is used.
            </para>

            <para>
                It's also possible to specify the default query string encoding with
                <methodname>Zend_Search_Lucene_Search_QueryParser::setDefaultEncoding()</methodname>
                method:

                <programlisting language="php"><![CDATA[
Zend_Search_Lucene_Search_QueryParser::setDefaultEncoding('iso-8859-5');
...
$userQuery = Zend_Search_Lucene_Search_QueryParser::parse($queryStr);
]]></programlisting>
            </para>

            <para>
                <methodname>Zend_Search_Lucene_Search_QueryParser::getDefaultEncoding()</methodname>
                returns the current default query string encoding (the empty string means "current
                locale").
            </para>
        </sect3>
    </sect2>

    <sect2 id="zend.search.lucene.searching.results">
        <title>Search Results</title>

        <para>
            The search result is an array of
            <classname>Zend_Search_Lucene_Search_QueryHit</classname> objects. Each of these has two
            properties: <code>$hit->id</code> is a document number within the index and
            <code>$hit->score</code> is a score of the hit in a search result. The results are
            ordered by score (descending from highest score).
        </para>

        <para>
            The <classname>Zend_Search_Lucene_Search_QueryHit</classname> object also exposes each
            field of the <classname>Zend_Search_Lucene_Document</classname> found in the search as a
            property of the hit. In the following example, a hit is returned with two fields from
            the corresponding document: title and author.
        </para>

        <programlisting language="php"><![CDATA[
$index = Zend_Search_Lucene::open('/data/my_index');

$hits = $index->find($query);

foreach ($hits as $hit) {
    echo $hit->score;
    echo $hit->title;
    echo $hit->author;
}
]]></programlisting>

        <para>
            Stored fields are always returned in UTF-8 encoding.
        </para>

        <para>
            Optionally, the original <classname>Zend_Search_Lucene_Document</classname> object can
            be returned from the <classname>Zend_Search_Lucene_Search_QueryHit</classname>.
            You can retrieve stored parts of the document by using the
            <methodname>getDocument()</methodname> method of the index object and then get them by
            <methodname>getFieldValue()</methodname> method:
        </para>

        <programlisting language="php"><![CDATA[
$index = Zend_Search_Lucene::open('/data/my_index');

$hits = $index->find($query);
foreach ($hits as $hit) {
    // return Zend_Search_Lucene_Document object for this hit
    echo $document = $hit->getDocument();

    // return a Zend_Search_Lucene_Field object
    // from the Zend_Search_Lucene_Document
    echo $document->getField('title');

    // return the string value of the Zend_Search_Lucene_Field object
    echo $document->getFieldValue('title');

    // same as getFieldValue()
    echo $document->title;
}
]]></programlisting>

        <para>
            The fields available from the <classname>Zend_Search_Lucene_Document</classname> object
            are determined at the time of indexing. The document fields are either indexed, or
            index and stored, in the document by the indexing application
            (e.g. LuceneIndexCreation.jar).
        </para>

        <para>
            Note that the document identity ('path' in our example) is also stored
            in the index and must be retrieved from it.
        </para>
    </sect2>

    <sect2 id="zend.search.lucene.searching.results-limiting">
        <title>Limiting the Result Set</title>

        <para>
            The most computationally expensive part of searching is score calculation. It may take
            several seconds for large result sets (tens of thousands of hits).
        </para>

        <para>
            <classname>Zend_Search_Lucene</classname> gives the possibility to limit result set size
            with <methodname>getResultSetLimit()</methodname> and
            <methodname>setResultSetLimit()</methodname> methods:

            <programlisting language="php"><![CDATA[
$currentResultSetLimit = Zend_Search_Lucene::getResultSetLimit();

Zend_Search_Lucene::setResultSetLimit($newLimit);
]]></programlisting>

            The default value of 0 means 'no limit'.
        </para>

        <para>
            It doesn't give the 'best N' results, but only the 'first N'

            <footnote>
                <para>
                    Returned hits are still ordered by score or by the specified order, if given.
                </para>
            </footnote>.
        </para>
    </sect2>

    <sect2 id="zend.search.lucene.searching.results-scoring">
        <title>Results Scoring</title>

        <para>
            <classname>Zend_Search_Lucene</classname> uses the same scoring algorithms as Java
            Lucene. All hits in the search result are ordered by score by default. Hits with greater
            score come first, and documents having higher scores should match the query more
            precisely than documents having lower scores.
        </para>

        <para>
            Roughly speaking, search hits that contain the searched term or phrase more frequently
            will have a higher score.
        </para>

        <para>
            A hit's score can be retrieved by accessing the <code>score</code> property of the hit:
        </para>

        <programlisting language="php"><![CDATA[
$hits = $index->find($query);

foreach ($hits as $hit) {
    echo $hit->id;
    echo $hit->score;
}
]]></programlisting>

        <para>
            The <classname>Zend_Search_Lucene_Search_Similarity</classname> class is used to
            calculate the score for each hit. See <link
                linkend="zend.search.lucene.extending.scoring">Extensibility. Scoring
                Algorithms</link> section for details.
        </para>
    </sect2>

    <sect2 id="zend.search.lucene.searching.sorting">
        <title>Search Result Sorting</title>

        <para>
            By default, the search results are ordered by score. The programmer can change this
            behavior by setting a sort field (or a list of fields), sort type and sort order
            parameters.
        </para>

        <para>
            <code>$index->find()</code> call may take several optional parameters:

            <programlisting language="php"><![CDATA[
$index->find($query [, $sortField [, $sortType [, $sortOrder]]]
                    [, $sortField2 [, $sortType [, $sortOrder]]]
             ...);
]]></programlisting>
        </para>

        <para>
             A name of stored field by which to sort result should be passed as the
             <varname>$sortField</varname> parameter.
        </para>

        <para>
            <varname>$sortType</varname> may be omitted or take the following enumerated values:
            <constant>SORT_REGULAR</constant> (compare items normally- default value),
            <constant>SORT_NUMERIC</constant> (compare items numerically),
            <constant>SORT_STRING</constant> (compare items as strings).
        </para>

        <para>
            <varname>$sortOrder</varname> may be omitted or take the following enumerated values:
            <constant>SORT_ASC</constant> (sort in ascending order- default value),
            <constant>SORT_DESC</constant> (sort in descending order).
        </para>

        <para>
            Examples:

            <programlisting language="php"><![CDATA[
$index->find($query, 'quantity', SORT_NUMERIC, SORT_DESC);
]]></programlisting>
            <programlisting language="php"><![CDATA[
$index->find($query, 'fname', SORT_STRING, 'lname', SORT_STRING);
]]></programlisting>
            <programlisting language="php"><![CDATA[
$index->find($query, 'name', SORT_STRING, 'quantity', SORT_NUMERIC, SORT_DESC);
]]></programlisting>
        </para>

        <para>
            Please use caution when using a non-default search order; the query needs to retrieve
            documents completely from an index, which may dramatically reduce search performance.
        </para>
    </sect2>

    <sect2 id="zend.search.lucene.searching.highlighting">
        <title>Search Results Highlighting</title>

        <para>
            <classname>Zend_Search_Lucene</classname> provides two options for search results
            highlighting.
        </para>

        <para>
            The first one is utilizing <classname>Zend_Search_Lucene_Document_Html</classname> class
            (see <link linkend="zend.search.lucene.index-creation.html-documents">HTML documents
                section</link> for details) using the following methods:

            <programlisting language="php"><![CDATA[
/**
 * Highlight text with specified color
 *
 * @param string|array $words
 * @param string $colour
 * @return string
 */
public function highlight($words, $colour = '#66ffff');
]]></programlisting>

            <programlisting language="php"><![CDATA[
/**
 * Highlight text using specified View helper or callback function.
 *
 * @param string|array $words  Words to highlight. Words could be organized
                               using the array or string.
 * @param callback $callback   Callback method, used to transform
                               (highlighting) text.
 * @param array    $params     Array of additionall callback parameters passed
                               through into it (first non-optional parameter
                               is an HTML fragment for highlighting)
 * @return string
 * @throws Zend_Search_Lucene_Exception
 */
public function highlightExtended($words, $callback, $params = array())
]]></programlisting>
        </para>

        <para>
            To customize highlighting behavior use <methodname>highlightExtended()</methodname>
            method with specified callback, which takes one or more parameters

            <footnote>
                <para>
                    The first is an HTML fragment for highlighting and others are callback behavior
                    dependent. Returned value is a highlighted HTML fragment.
                </para>
            </footnote>
            , or extend <classname>Zend_Search_Lucene_Document_Html</classname> class and redefine
            <methodname>applyColour($stringToHighlight, $colour)</methodname> method used as a
            default highlighting callback.

            <footnote>
                <para>
                    In both cases returned HTML is automatically transformed into valid
                    <acronym>XHTML</acronym>.
                </para>
            </footnote>
        </para>

        <para>
            <link linkend="zend.view.helpers">View helpers</link> also can be used as callbacks in
            context of view script:

            <programlisting language="php"><![CDATA[
$doc->highlightExtended('word1 word2 word3...', array($this, 'myViewHelper'));
]]></programlisting>
        </para>

        <para>
            The result of highlighting operation is retrieved by
            <code>Zend_Search_Lucene_Document_Html->getHTML()</code> method.
        </para>

        <note>
            <para>
                Highlighting is performed in terms of current analyzer. So all forms of the word(s)
                recognized by analyzer are highlighted.
            </para>

            <para>
                E.g. if current analyzer is case insensitive and we request to highlight 'text'
                word, then 'text', 'Text', 'TEXT' and other case combinations will be highlighted.
            </para>

            <para>
                In the same way, if current analyzer supports stemming and we request to highlight
                'indexed', then 'index', 'indexing', 'indices' and other word forms will be
                highlighted.
            </para>

            <para>
                On the other hand, if word is skipped by current analyzer (e.g. if short words
                filter is applied to the analyzer), then nothing will be highlighted.
            </para>
        </note>

        <para>
            The second option is to use
            <code>Zend_Search_Lucene_Search_Query->highlightMatches(string $inputHTML[,
                $defaultEncoding = 'UTF-8'[,
                Zend_Search_Lucene_Search_Highlighter_Interface $highlighter]])</code> method:

            <programlisting language="php"><![CDATA[
$query = Zend_Search_Lucene_Search_QueryParser::parse($queryStr);
$highlightedHTML = $query->highlightMatches($sourceHTML);
]]></programlisting>
        </para>

        <para>
            Optional second parameter is a default HTML document encoding. It's used if encoding is
            not specified using Content-type HTTP-EQUIV meta tag.
        </para>

        <para>
            Optional third parameter is a highlighter object which has to implement
            <classname>Zend_Search_Lucene_Search_Highlighter_Interface</classname> interface:

            <programlisting language="php"><![CDATA[
interface Zend_Search_Lucene_Search_Highlighter_Interface
{
    /**
     * Set document for highlighting.
     *
     * @param Zend_Search_Lucene_Document_Html $document
     */
    public function setDocument(Zend_Search_Lucene_Document_Html $document);

    /**
     * Get document for highlighting.
     *
     * @return Zend_Search_Lucene_Document_Html $document
     */
    public function getDocument();

    /**
     * Highlight specified words (method is invoked once per subquery)
     *
     * @param string|array $words  Words to highlight. They could be
                                   organized using the array or string.
     */
    public function highlight($words);
}
]]></programlisting>

            Where <classname>Zend_Search_Lucene_Document_Html</classname> object is an object
            constructed from the source HTML provided to the
            <classname>Zend_Search_Lucene_Search_Query->highlightMatches()</classname> method.
        </para>

        <para>
            If <varname>$highlighter</varname> parameter is omitted, then
            <classname>Zend_Search_Lucene_Search_Highlighter_Default</classname> object is
            instantiated and used.
        </para>

        <para>
            Highlighter <methodname>highlight()</methodname> method is invoked once per subquery, so
            it has an ability to differentiate highlighting for them.
        </para>

        <para>
            Actually, default highlighter does this walking through predefined color table. So you
            can implement your own highlighter or just extend the default and redefine color table.
        </para>

        <para>
            <code>Zend_Search_Lucene_Search_Query->htmlFragmentHighlightMatches()</code> has similar
            behavior. The only difference is that it takes as an input and returns HTML fragment
            without &lt;>HTML>, &lt;HEAD>, &lt;BODY> tags. Nevertheless, fragment is automatically
            transformed to valid <acronym>XHTML</acronym>.
        </para>
    </sect2>
</sect1>