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+ <h1 class="graphic"><img src="cql_files/sru-title.gif" alt="SRU: Search/Retrieve via URL - SRU Version 1.1 - 13th February 2004" height="60" width="740"></h1>
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+ <div id="top-bread"> <a href="http://www.loc.gov/standards/sru/index.html">Home</a> >> <!-- InstanceBeginEditable name="topbreadcrumb" --><span class="selected">CQL</span><!-- InstanceEndEditable --></div>
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+ <h1>Common Query Language</h1>
+ <p><strong>CQL <a href="http://www.loc.gov/standards/sru/version.html">Version</a> 1.1</strong> <em>13th February
+ 2004</em></p>
+ <p class="box"><a href="#sample">Sample Queries</a> - <a href="#bnf">BNF</a> - <a href="#rules"> Rules</a> - <a href="#features"> Features</a> - <a href="#conformance">Conformance</a>
+- <a href="#context"> Context Sets</a> - <a href="http://www.loc.gov/standards/sru/cql/cql-context-set.html"> the
+ CQL Context Set</a> - <a href="#relations">Relations</a> <a href="#relmodifiers">Modifiers</a> - <a href="#masking">Masking</a> - <a href="#resultset">Result
+ Sets</a> - <a href="#proximity">Proximity</a> - Tutorial (temporarily unavailable)</p>
+ <p>CQL is a formal language for representing queries to information retrieval
+ systems such as web indexes, bibliographic catalogs and museum collection
+ information. The design objective is that queries be human readable and
+ writable, and that the language be intuitive while maintaining the expressiveness
+ of more complex languages.</p>
+ <p>Traditionally, query languages have fallen into two camps: Powerful, expressive
+ languages, not easily readable nor writable by non-experts (e.g. SQL, PQF,
+ and XQuery);or simple and intuitive languages not powerful enough to express
+ complex concepts (e.g. CCL and google). CQL tries to combine simplicity
+ and intuitiveness of expression for simple, every
+ day queries, with the richness of more expressive languages to accommodate
+ complex concepts when necessary.</p>
+ <hr>
+ <h3><a name="sample"></a> Sample Queries</h3>
+ <p>Following are examples of simple CQL queries. These are all self-explanatory: </p>
+ <p class="box2">dinosaur<br>
+"complete dinosaur"<br>
+ title = "complete dinosaur"<br>
+ title exact "the complete dinosaur"<br>
+ dinosaur or bird<br>
+ dinosaur and "ice age"<br>
+ dinosaur not reptile <br>
+ dinosaur and bird or dinobird <br>
+ (bird or dinosaur) and (feathers or scales)<br>
+"feathered dinosaur" and (yixian or jehol) <br>
+ publicationYear < 1980 <br>
+ lengthOfFemur > 2.4<br>
+ bioMass >= 100 </p>
+ <p>The following are a bit more complicated:</p>
+ <table align="center" border="1" cellpadding="5" cellspacing="0" width="95%">
+ <tbody><tr>
+ <th scope="col" bgcolor="#fff9e5" width="50%">Example</th>
+ <th scope="col" bgcolor="#fff9e5" width="50%">Explanation</th>
+ </tr>
+ <tr>
+ <td scope="row"><p>title all "complete dinosaur"</p></td>
+ <td><p>Title contains all of the words: "complete", and "dinosaur"</p></td>
+ </tr>
+ <tr>
+ <td scope="row"><p><br>
+ title any "dinosaur bird reptile"</p></td>
+ <td><p>Title contains any of the words: "dinosaur", "bird",
+ or "reptile"</p></td>
+ </tr>
+ <tr>
+ <td scope="row"><p>(caudal or dorsal) prox vertebra</p></td>
+ <td><p><em>A proximity query: either "caudal" or "dorsal" near
+ 'vertebra"</em></p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row">
+ <p>ribs prox/distance<=5 chevrons </p>
+ </td>
+ <td><p><em>A more specific proximity query: "ribs" within
+ 5 words of "chevrons"</em></p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p>ribs prox/unit=sentence chevrons</p>
+ </td>
+ <td>
+ <p><em>"ribs" in the same sentence as "chevrons"</em></p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row">
+ <p>ribs prox/distance>0/unit=paragraph chevrons </p>
+ </td>
+ <td><p><em>"ribs" and "chevrons" occuring
+ in the same document in different paragraphs</em></p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p>subject any/relevant "fish frog"</p>
+ </td>
+ <td><p><em>find documents that would seem relevant
+ either to "fish" or "frog"</em></p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p>subject any/rel.lr "fish frog"</p>
+ </td>
+ <td><p><em>Same as previous, but use a specific relevance
+ algorithm (linear regression)</em></p>
+ </td>
+ </tr>
+ </tbody></table>
+ <hr>
+ <h2><a name="bnf"></a>Formal Definition: CQL BNF</h2>
+ <p>Following is the Backus Naur Form (BNF) definition for CQL. ["::=" represents
+ "is defined as"]</p>
+ <table border="0" cellpadding="5" cellspacing="0" width="95%">
+ <tbody>
+ <tr>
+ <td scope="row" align="right" width="24%">
+ <p>cqlQuery</p>
+ </td>
+ <td width="1%"><p>::=</p>
+ </td>
+ <td width="75%"><p>prefixAssignment cqlQuery | scopedClause </p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right">
+ <p>prefixAssignment</p>
+ </td>
+ <td><p>::=</p>
+ </td>
+ <td><p>'>' prefix '=' uri | '>' uri</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right">
+ <p>scopedClause</p>
+ </td>
+ <td><p>::=</p>
+ </td>
+ <td><p>scopedClause booleanGroup searchClause | searchClause</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right">
+ <p>booleanGroup</p>
+ </td>
+ <td><p>::=</p>
+ </td>
+ <td><p>boolean [modifierList]</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right" valign="top">
+ <p>boolean</p>
+ </td>
+ <td valign="top"><p>::=</p>
+ </td>
+ <td><p>'and' | 'or' | 'not' | 'prox'</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right" valign="top">
+ <p>searchClause</p>
+ </td>
+ <td valign="top"><p>::=</p>
+ </td>
+ <td>
+ <p>'(' cqlQuery ')'<br>
+ | index relation searchTerm<br>
+ | searchTerm</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right">
+ <p>relation</p>
+ </td>
+ <td><p>::=</p>
+ </td>
+ <td><p>comparitor [modifierList]</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right">
+ <p>comparitor</p>
+ </td>
+ <td><p>::=</p>
+ </td>
+ <td><p>comparitorSymbol | namedComparitor</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right">
+ <p>comparitorSymbol</p>
+ </td>
+ <td><p>::=</p>
+ </td>
+ <td><p>'=' | '>' | '<' | '>=' | '<=' | '<>'</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right">
+ <p>namedComparitor</p>
+ </td>
+ <td><p>::=</p>
+ </td>
+ <td><p>identifier</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right">
+ <p>modifierList</p>
+ </td>
+ <td><p>::=</p>
+ </td>
+ <td><p>modifierList modifier<strong> | </strong>modifier</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right">
+ <p>modifier</p>
+ </td>
+ <td><p>::=</p>
+ </td>
+ <td><p>'/' modifierName [comparitorSymbol modifierValue] </p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right"><p align="right">prefix, uri, modifierName, modifierValue, searchTerm,
+ index</p>
+ </td>
+ <td valign="top"><p>::=</p>
+ </td>
+ <td valign="top"><p>term</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right">
+ <p>term</p>
+ </td>
+ <td><p>::=</p>
+ </td>
+ <td><p>identifier | 'and' | 'or' | 'not' | 'prox'</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right" valign="top">
+ <p>identifier</p>
+ </td>
+ <td valign="top"><p>::=</p>
+ </td>
+ <td><p>charString1 | charString2</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right" valign="top">
+ <p><em>charString1</em></p>
+ </td>
+ <td valign="top"><p>:=</p>
+ </td>
+ <td><p><em>Any sequence of characters that does not include any of
+ the following:</em> </p>
+ <blockquote><em>whitespace<br>
+ </em><em>( (open parenthesis )</em><br>
+ <em>) (close parenthesis)</em><br>
+ <em>=<br>
+ </em><em><<br>
+ </em><em>></em><br>
+ <em>'"' (double quote)<br>
+ </em><em>/</em></blockquote> <p><em> If the final sequence is a reserved word, that token is
+ returned instead. Note that '.' (period) may be included, and
+ a sequence of digits is also permitted. Reserved words are
+ 'and', 'or', 'not', and 'prox' (case insensitive). When a reserved
+ word is used in a search term, case is preserved. </em> </p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row" align="right" valign="top">
+ <p><em>charString2</em></p>
+ </td>
+ <td valign="top"><p>:=</p>
+ </td>
+ <td><p><em>Double quotes enclosing a sequence of any characters except
+ double quote (unless preceded by backslash (\)). Backslash escapes
+ the character following it. The resultant value includes all
+ backslash characters except those releasing a double quote (this
+ allows other systems to interpret the backslash character). The
+ surrounding double quotes are not included. </em></p>
+ </td>
+ </tr>
+ </tbody>
+ </table>
+ <hr>
+ <h2><a name="rules"></a>General Rules</h2>
+ <ol>
+ <li>
+ <p><strong>CQL Query<br>
+ </strong>A CQL query is essentially a search clause, or multiple search
+ clauses connected by boolean operators. (In addition it may include
+ prefix assignments which assign short names to known contexts. See <a href="#context">context
+ sets</a>.)</p>
+ </li>
+ <li>
+ <p><strong>Search Clause</strong><br>
+ A search clause consists of an index, relation, and search term, or a search
+ term alone. Thus every search clause has a search term, but both the
+ index and relation may be omitted - the clause must include either
+ both or neither of the index and relation. (Note that the use of the "index" concept
+ in CQL is not intended to have any implementation implications; it does
+ not imply the presence of a physical index.)</p>
+ <p> Examples: <br>
+ Index/relation/search term: <strong>title
+= cat</strong><br>
+ Search term only: <strong>cat</strong>
+
+ </p></li><li>
+ <p><strong>Search Term</strong><br>
+ Search terms <em>may</em> be enclosed in double quotes. Search terms <em>must</em> be
+ enclosed in double quotes if they contain any of the following characters: < > =
+ / ( ) and whitespace. The search term may be empty, but must be present
+ in a search clause. An empty search term is expressed as "" and has no
+ defined semantics. </p>
+ </li>
+ <li>
+ <p><strong>Index</strong> <strong>Name</strong><br>
+ An index name always includes a base name and may also include a prefix,
+ which provides a context for the index name, the name of the <a href="#context">context
+ set</a> of which the index is a part. If the context is not supplied,
+ it is determined by the server. If the index is not supplied it
+ is determined by the server. (Note that the index may be omitted only
+ when the relation is also omitted. Either both must be supplied, or both
+ omitted.)</p>
+ <p> Examples:<br>
+ title = cat <em>context determined
+by the server</em><br>
+ dc.title = cat <em>index context is dc<br>
+ </em>cat <em>context and
+index determined by the server</em></p>
+ </li>
+ <li>
+ <p><strong>Relation<br>
+ </strong>The relation in a search clause specifies the relationship
+ between the index and search term. It also always includes a
+ base name and may also include a prefix providing a context for the
+ relation. If a relation is supplied with no accompanying context, the
+ context is 'cql' (the <a href="http://www.loc.gov/standards/sru/cql/cql-context-set.html">cql context
+ set</a>). If no relation is supplied, then cql.scr (server choice)
+ is assumed, which means that the relation is determined by the server.
+ (Note that the relation may be omitted only when the index is also
+ omitted. Either both must be supplied, or both
+ omitted.)</p>
+ <p></p>
+ <p> Examples:<br>
+ title = cat <em> context for relation is 'cql' ; fully qualified
+relation is cql.=<br>
+ </em>title cql.any cat <em>relation is 'any';
+relation context is 'cql'. Equivalent to: </em>title any cat<em><br>
+ cat index and relation are determined
+by the server (formally the relation is 'cql.scr')</em></p>
+ </li>
+ <li><a name="relmods"></a>
+ <strong>Relation Modifiers</strong><br>
+ Relation modifiers may accompany a relation. These also may be accompanied
+ by a context. If a context is not supplied for a modifier, the
+ default is the <a href="http://www.loc.gov/standards/sru/cql/cql-context-set.html">cql context set</a>. Relation
+ modifiers are separated from each other and from the relation by slashes
+ ( /). Whitespace may be present on either side of a / character, but
+ the relation plus modifiers group may not end in a /.
+ <p> Examples:<br>
+ dc.title any/relevant/rel.CORI "cat fish" <br>
+ <em> the relation 'any'
+is modified by (1) 'relevant' whose context is 'cql' and (2) 'CORI' whose context
+is 'rel'.</em><br>
+ dc.author exact/stem "smith, j." <em>the
+relation 'exact' is modified by 'stem' whose context is 'cql'</em>.<em><br>
+ </em></p>
+ </li>
+ <li>
+ <p><strong>Boolean Operators</strong><br>
+ Search clauses may be linked by boolean operators. These are: <strong>and</strong>, <strong>or</strong>, <strong>not</strong> and <strong>prox</strong>.
+ (Note that <strong>not</strong> is really and-not, that is, it may
+ not be used as a unary operator.) Boolean operators all have the same
+ precedence; they are evaluated left-to-right. Parentheses
+ may
+ be used
+ to
+ overide left-to-right
+ evaluation.</p>
+ </li>
+ <li>
+ <p><strong>Boolean Modifiers</strong><br>
+ As a relation may have modifiers, similiarly, a
+ boolean operator may have modifiers, separated by '/' characters. Boolean
+ modifiers may come from
+ any context
+ set. If
+ not supplied, the context is the <a href="http://www.loc.gov/standards/sru/cql/cql-context-set.html">CQL
+ context set</a>. (Note that Boolean operators themselves
+ are limited to the built-in set of four.)</p>
+ <p> Example: dc.title=cat and/rel.sum dc.title=dog</p></li>
+ <li>
+ <p><strong>Case Insensitive</strong> <br>
+ All parts of CQL are case insensitive apart from user supplied search terms,
+ which may or may not be case sensitive. 'OR','or', 'Or' and 'oR' are
+ all the same boolean operator, just as 'dc.title', 'DC.Title' and 'dC.TiTLe'
+ are all the same context set plus index name. </p>
+ </li></ol>
+ <hr>
+ <h2><a name="features"></a>Additional CQL Features</h2>
+ <p>The following are all formally defined by the CQL context set but described
+ here for convenience.</p>
+ <h3><a name="relations"></a>Relations </h3>
+ <p><strong>For ordered (e.g. numeric) terms: </strong><strong><br>
+<</strong>, <strong>></strong>, <strong><=</strong>, <strong>>=</strong>,
+and <strong><></strong> mean "less than", "greater than", "less
+or equal", "greater or equal", and "not equal". </p>
+ <p></p>
+ <p><strong>when the term is a list of words</strong>: </p>
+ <ul>
+ <li>
+ <p><strong> '='</strong> is used for word adjacency -- the words
+ appear in that order with no others intervening. (Note the dual
+ use of '=', it is used for numeric equality as described above.) </p></li>
+ <li>
+ <p> <strong>'any</strong>' means "any of these words" </p></li>
+ <li>
+ <p> '<strong>all</strong>' means "all of these words"</p>
+ </li></ul>
+ <p><strong>When the term is a character string:<br>
+ </strong><strong>'</strong><strong>exact</strong>' is used for exact string
+ matching.
+ </p>
+ <p><strong>When the term has multiple dimensions:<br>
+ </strong><strong>'within</strong>' may be used to search for values that
+ fall within the range, area or volume described by the search
+ term.</p>
+ <p>
+ <strong>When the index's data has multiple dimensions:<br>
+ </strong><strong>'encloses</strong>' may be used to search for values of
+ the database's term fully encloses the search term.
+ </p>
+
+
+ Examples:
+ <table border="1" cellpadding="5" cellspacing="0" width="95%">
+ <tbody><tr bgcolor="#fff9e5">
+ <th scope="col" width="28%"><em>This query </em></th>
+ <th scope="col" width="35%"><em>Would match this </em></th>
+ <th scope="col" width="37%"><em>but not this</em></th>
+ </tr>
+ <tr>
+ <td scope="row"><p><strong>title = "cat in the hat"</strong></p>
+ </td>
+ <td><p> "a day in the life of the cat in the hat"</p>
+ </td>
+ <td><p>"hat in the cat" or "cat in the green hat"</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p><strong>title all "cat hat"</strong></p>
+ </td>
+ <td><p>"hat in the cat"</p>
+ </td>
+ <td><p>"cat in the grass"</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p><strong>title any "cat hat"</strong></p>
+ </td>
+ <td><p>"cat in the grass"</p>
+ </td>
+ <td><p>"dog in the grass"</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p><strong>title exact "cat in the hat"</strong></p>
+ </td>
+ <td><p>"cat in the hat"</p>
+ </td>
+ <td><p>"a day in the life of the cat in the hat"</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p><strong>date within "2002 2005"</strong></p></td>
+ <td><p>2004</p></td>
+ <td><p>2006</p></td>
+ </tr>
+ <tr>
+ <td scope="row"><p><strong>dateRange encloses 2003</strong></p></td>
+ <td><p>"2002 2005"</p></td>
+ <td><p>"2004 2005"</p></td>
+ </tr>
+ </tbody></table>
+ <h3><br>
+ <a name="relmodifiers"></a>Relation Modifiers <strong>- Term Functions</strong></h3>
+ <p>These relation modifiers request that the server perform some algorithm
+ on the term before processing. </p>
+ <ul>
+ <li>
+ <p><strong>stem</strong><br>
+ The server should apply a stemming algorithm to the words within the term.
+ for example, walked, walking, walker <i>etc.</i> would all be represented
+ by the stem word walk. This allows a search like title =/stem "these
+ completed dinosaurs" to match <i>The Complete Dinosaur</i>. </p></li>
+ <li>
+ <p><strong>relevant</strong><br>
+ The server should use a relevancy algorithm for determining matches and
+ the order of the result set. </p>
+ <p> Example: <em>subject any/relevant "fish frog"</em><br>
+ would find records relevant to "fish" or "frog" and order
+ the result set by relevance to fish or frog.<i><br>
+ <br>
+ </i></p>
+ </li></ul>
+ <h3><strong>Relation Modifiers - Qualifiers</strong></h3>
+ <p> These modifiers qualify the relation to more precisely determine its
+ semantics. </p>
+ <ul>
+ <li>
+ <p><strong>word</strong><br>
+ The term consists of words (rather than being an opaque string). </p>
+ </li>
+ <li>
+ <p><strong>string</strong><br>
+ The term is a single item, and should not be broken up. </p></li>
+ <li>
+ <p><strong>isoDate</strong><br>
+ Each item within the term conforms to the ISO 8601 specification for expressing
+ dates. </p></li>
+ <li>
+ <p><strong>number</strong><br>
+ Each item within the term is a number. </p></li>
+ <li>
+ <p><strong>uri</strong><br>
+ Each item within the term is a URI. </p></li>
+ <li>
+ <p><strong>masked</strong><br>
+ This means that the masking rules (see next) apply. Masking is assumed
+ even if not specified, unless 'unmasked' is specified (so there is never
+ any reason to include 'masked').</p>
+ </li><li><strong>unmasked </strong><br>
+ Do not apply masking rules.
+ </li></ul>
+ <h3><a name="masking"></a>Masking Rules</h3>
+ <ul>
+ <li>
+ <p>A single asterisk (*) is used to mask zero or more characters. </p></li>
+ <li>
+ <p>A single question mark (?) is used to mask a single character, thus
+ N consecutive question-marks means mask N characters. </p></li>
+ <li>
+ <p>Carat/hat (^) is used as an anchor character for terms that are word
+ lists, that is, where the relation is 'all' or 'any', or '=' when used
+ for word adjacency. It may not be used to anchor a string, that is,
+ when relation is 'exact' (string matches are, by definition, anchored).
+ It may occur at the beginning or end of a word (with no intervening
+ space) to mean right or left anchored."^" has no special meaning when
+ it occurs within a word (not at the beginning or end) or string but
+ must be escaped nevertheless. </p>
+ </li>
+ <li>
+ <p> Backslash (\) is used to escape '*', '?', quote (") and '^' , as
+ well as itself. The use of a backslash not followed immediately by
+ one of these characters is reserved for future definition.</p>
+ </li>
+ </ul>
+ <p>Masking examples: </p>
+ <ul>
+ <li>
+ <p>dc.title = c*t <i>(matches cat and coast etc.)</i></p></li>
+ <li>
+ <p>dc.title = c?t <i>(matches cat and cot, not coast or ct)</i><br>
+" ?" <i>(matches any single character)</i> </p></li>
+ <li>
+ <p>dc.title = "^cat in the hat" <i>(matches 'cat in the hat' where it
+ is at the beginning of the field)</i></p>
+ </li>
+ <li>
+ <p>dc.title any "^cat eats rat" <i>(matches 'cat eats rat', 'cat eats
+ dog', 'cat', but not 'rat eats cat')</i> </p>
+ </li>
+ <li>
+ <p>
+ dc.title any "^cat ^dog eats rat" <i>(matches 'cat eats rat', 'dog
+ eats cat', 'cat
+ loves bat', but not 'bat loves cat')</i> </p>
+ </li>
+ <li>
+ <p>dc.title = "\"Of Couse\" she said"</p>
+ </li>
+ </ul>
+ <h3><strong><a name="resultset"></a>Result Set Name Used in Query</strong></h3>
+ <p>A search clause may be a result set name. This is a special case, employing
+ the context set '<a href="http://www.loc.gov/z3950/agency/zing/cql/context-sets/cql.html">cql</a>'.
+ The index and relation are expressed as "cql.resultSetId =" and
+ the term is a result set name that has been returned by the server in the
+ 'resultSetName' parameter of the response. It may be used by itself in
+ a query to refer to an existing result set from which records are desired.
+ It may also be used in conjunction with other resultSetName clauses or
+ other indexes, combined by boolean operators. The semantics of resultSetId
+ with relations other than "=" is undefined. </p>
+ <p> Example: cql.resultSetId = "resultA" and cql.resultSetId = "resultB" </p>
+ <h3><strong><a name="proximity"></a>Proximity</strong></h3>
+ <p>The proximity boolean boolean operator is expressed in terms of distance,
+ unit, and ordering.</p>
+ <p>Examples:</p>
+ <ul>
+ <li> dc.title = "cat" prox/distance=1/unit=word dc.title
+ = "in"</li>
+ <li>"cat" prox/distance>2/ordered "hat" </li>
+ </ul>
+ <p><strong>distance</strong> takes the form:<br>
+ distance [relation] [value] <br>
+where relation is one of: "<", ">" ,"<=" ,">=" ,"=" , "<>"; <i>default "<="</i><br>
+and value is a non-negative integer; <i>default: 1 for word, zero otherwise</i></p>
+ <p><strong>unit</strong> takes the form<br>
+ unit=[value] <br>
+ where value is one of "word", "sentence", "paragraph", or "element"<i>(default "word"</i>),</p>
+ <p><strong>ordering</strong> is "ordered" or "unordered"; <i>default "unordered"</i></p>
+ <p> </p>
+ <hr>
+ <h2><a name="context"></a>CQL Context Sets</h2>
+ <p>Context sets permit CQL users to create their own indexes, relations,
+ relation modifiers and boolean modiers without fear of chosing the same
+ name as someone else and thereby having an ambiguous query. All of these
+ four aspects of CQL must come from a context set, however there are rules
+ for determining the prevailing default if one is not supplied. Context
+ sets allow CQL to be used by communities in ways which the designers could
+ not have foreseen, while still maintaining the same rules for parsing which
+ allow interoperability.</p>
+ <p>When defining a new context set, it is necessary to provide a description
+ of the semantics of each item within it. While context sets may contain
+ indexes, relations, relation modifiers and boolean modifiers, there is
+ no requirement that all should be present; in fact it is expected that
+ most context sets will only define indexes.</p>
+ <p>Each context set has a unique identifier, a URI. When sending the context
+ set in a query, a short form is used. These short names may be sent as
+ a mapping within the query itself (see next), or be published by the recipient
+ of the query in some protocol dependent fashion. The prefix 'cql' is reserved
+ for the CQL context set, but authors may wish to recommend a short name
+ for use with their set. </p>
+ <p> An index, relation, or modifier qualified by a context is represented
+ in the form <i>prefix</i>.<i>value</i>, where <i>prefix</i> is a short
+ name for a unique context set identifier. </p>
+ <p><strong>Binding Short Name to URI<br>
+ </strong>The binding of short name to
+ URI is defined either within the query or by the server. A prefix map
+ may occur at any place in the query and applies to anything which follows.
+ Example: </p>
+ <p class="box2">>dc="http://www.dublincore.org/" dc.title = "cat"</p>
+ <p>
+ </p><p>In the following query:
+ </p><p>
+
+ </p><p class="box2">>a="http:/x.com/y" a.title=cat and (>a="http:/f.com/g" a.title=hat)
+ and a.title=rat</p>
+ <p>
+ </p><p>both the "a" in "a.title=cat" and in "a.title=rat" refer
+ to http:/x.com/y, while the "a" in "a.title=rat" refers
+ to http:/f.com/g.</p>
+ <p> <strong>Default Context</strong><br>
+ When no context is attached to a relation, relation modifier,
+ or boolean modifier, the context is the cql context set. When no
+ context is attached to an index the context is determined by the server.</p>
+ <p><strong>Known Context Sets</strong><br>
+ The following context sets have been defined and made
+ public. If you wish to have your context set listed here, please provide
+ the information
+ to
+ the <a href="mailto:z950@loc.gov">SRU Maintenance Agency</a>.</p>
+ <table align="center" border="1" cellpadding="5" cellspacing="0" width="95%">
+ <tbody>
+ <tr>
+ <th scope="col" bgcolor="#fff9e5" width="15%">Short Name</th>
+ <th scope="col" bgcolor="#fff9e5" width="60%">Identifier</th>
+ <th scope="col" bgcolor="#fff9e5" width="25%">Reference</th>
+ </tr>
+ <tr>
+ <td scope="row"><p><strong>cql</strong></p>
+ </td>
+ <td><p>info:srw/cql-context-set/1/cql-v1.1</p>
+ </td>
+ <td><p><a href="http://www.loc.gov/standards/sru/cql/cql-context-set.html">CQL context set</a></p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p>dc</p>
+ </td>
+ <td><p>info:srw/cql-context-set/1/dc-v1.1</p>
+ </td>
+ <td><p><a href="http://www.loc.gov/standards/sru/cql/dc-context-set.html">Dublin Core Context Set</a></p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p>bath</p>
+ </td>
+ <td>
+ <p>http://zing.z3950.org/cql/bath/2.0/</p>
+ </td>
+ <td><p><a href="http://zing.z3950.org/srw/bath/2.0/#2">Bath Context
+ Set</a></p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p>zthes</p>
+ </td>
+ <td><p>http://zthes.z3950.org/cql/1.0/</p>
+ </td>
+ <td><p><a href="http://zthes.z3950.org/cql/">ZThes thesaurus context
+ set</a>, v1.0.</p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p>ccg</p>
+ </td>
+ <td><p>http://srw.cheshire3.org/contextSets/ccg/1.1/</p>
+ </td>
+ <td><p><a href="http://srw.cheshire3.org/contextSets/ccg/">Collectable
+ card games</a> </p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p>rec</p>
+ </td>
+ <td><p>info:srw/cql-context-set/2/rec-1.1</p>
+ </td>
+ <td><p><a href="http://srw.cheshire3.org/contextSets/rec/1.1/">Record metadata</a></p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p>net</p>
+ </td>
+ <td><p>info:srw/cql-context-set/2/net-1.0</p>
+ </td>
+ <td><p><a href="http://srw.cheshire3.org/contextSets/net/">Network
+ resource information</a></p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p>music</p>
+ </td>
+ <td><p>info:srw/cql-context-set/3/music-1.0 </p>
+ </td>
+ <td><p><a href="http://www.ceridwen.com/srw/music-contextset.html">Music
+ Context Set</a></p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p>rel</p>
+ </td>
+ <td><p>info:srw/cql-context-set/2/relevance-1.0</p>
+ </td>
+ <td><p><a href="http://srw.cheshire3.org/contextSets/rel/">Relevance
+ Ranking</a></p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p>zeerex</p>
+ </td>
+ <td>
+ <p>info:srw/cql-context-set/2/zeerex-1.1</p>
+ </td>
+ <td><p><a href="http://srw.cheshire3.org/contextSets/ZeeRex/">ZeeRex
+ Context Set</a></p>
+ </td>
+ </tr>
+ <tr>
+ <td scope="row"><p>marc</p>
+ </td>
+ <td><p>info:srw/cql-context-set/1/marc-1.0</p></td>
+ <td><p><a href="http://www.loc.gov/standards/sru/cql/marc-context-set.html">MARC Context Set</a></p></td>
+ </tr>
+ </tbody>
+ </table>
+ <p>
+ </p><hr>
+ <h2><a name="conformance"></a>Conformance</h2>
+ <p>In order to claim conformance to CQL a server must support one of the
+ following three levels:</p>
+ <p><strong>Level 0</strong></p>
+ <ol>
+ <li>
+ <p>Must be able to process a term-only query.<br>
+ (The term is either a single word or if multiple words separated by spaces
+ then the entire search term is quoted). If the term includes quote marks,
+ they must be a escaped by preceding them with a backslash, e.g."raising
+ the \"titanic\"".)</p>
+ </li>
+ <li>
+ <p>If an unsupported query is supplied, must be able to respond with
+ a diagnostic to say that the query is not supported.</p>
+ </li>
+ </ol>
+ <p><strong>Level 1</strong></p>
+ <ol>
+ <li>
+ <p> Support for Level 0.</p>
+ </li>
+ <li>
+ <p> Ability to <em>parse</em> both: <br>
+ (a) search clauses consisting of 'index relation searchTerm'; and <br>
+ (b) queries where search terms are combined with booleans, e.g. "term1
+ AND term2" </p></li>
+ <li>
+ <p><em>Support</em> for at least one of (a) and (b). </p></li>
+ </ol>
+ <p>Note that (b) does not necessarily include queries such as:</p>
+ <blockquote>
+ <p> index relation term1 AND index relation term2</p>
+ </blockquote>
+ <p> but rather queries where the search clauses are terms-only (do not include
+ index or relation).</p>
+ <p><strong>Level 2</strong></p>
+ <ol>
+ <li>
+ <p> Support for Level 1. </p>
+ </li>
+ <li>
+ <p>Ability to <em>parse</em> all of CQL and respond with appropriate
+ diagnostics.</p>
+ </li>
+ </ol>
+ <p>Note that Level 2 does not require <em>support</em> for all of CQL, it
+ requires that the server be able to <em>parse</em> all of CQL (and respond
+ with proper diagnostics for the parts not supported.).</p>
+ <!-- InstanceEndEditable -->
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