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diff --git a/www/wiki/extensions/SemanticMediaWiki/src/SPARQLStore/QueryEngine/Condition/Condition.php b/www/wiki/extensions/SemanticMediaWiki/src/SPARQLStore/QueryEngine/Condition/Condition.php
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+<?php
+
+namespace SMW\SPARQLStore\QueryEngine\Condition;
+
+/**
+ * Abstract class that represents a SPARQL (sub-)pattern and relevant pieces
+ * of associated information for using it in query building.
+ *
+ * @ingroup SMWStore
+ *
+ * @license GNU GPL v2+
+ * @since 1.6
+ *
+ * @author Markus Krötzsch
+ */
+abstract class Condition {
+
+	/**
+	 * If results could be ordered by the things that this condition
+	 * matches, then this is the name of the variable to use in ORDER BY.
+	 * Otherwise it is ''.
+	 * @note SPARQL variable names do not include the initial "?" or "$".
+	 * @var string
+	 */
+	public $orderByVariable = '';
+
+	/**
+	 * Array that relates sortkeys (given by the users, i.e. property
+	 * names) to variable names in the generated SPARQL query.
+	 * Format sortkey => variable name
+	 * @var array
+	 */
+	public $orderVariables = [];
+
+	/**
+	 * Associative array of additional conditions that should not narrow
+	 * down the set of results, but that introduce some relevant variable,
+	 * typically for ordering. For instance, selecting the sortkey of a
+	 * page needs only be done once per query. The array is indexed by the
+	 * name of the (main) selected variable, e.g. "v42sortkey" to allow
+	 * elimination of duplicate weak conditions that aim to introduce this
+	 * variable.
+	 * @var array of format "condition identifier" => "condition"
+	 */
+	public $weakConditions = [];
+
+	/**
+	 * Associative array of additional conditions that should can narrow
+	 * down the set of results,
+	 *
+	 * @var array of format "condition identifier" => "condition"
+	 */
+	public $cogentConditions = [];
+
+	/**
+	 * Associative array of additional namespaces that this condition
+	 * requires to be declared
+	 * @var array of format "shortName" => "namespace URI"
+	 */
+	public $namespaces = [];
+
+	/**
+	 * Get the SPARQL condition string that this object represents. This
+	 * does not include the weak conditions, or additional formulations to
+	 * match singletons (see SMWSparqlSingletonCondition).
+	 *
+	 * @return string
+	 */
+	abstract public function getCondition();
+
+	/**
+	 * Tell whether the condition string returned by getCondition() is safe
+	 * in the sense that it can be used alone in a SPARQL query. This
+	 * requires that all filtered variables occur in some graph pattern,
+	 * and that the condition is not empty.
+	 *
+	 * @return boolean
+	 */
+	abstract public function isSafe();
+
+	public function addNamespaces( array $namespaces ) {
+		$this->namespaces = array_merge( $this->namespaces, $namespaces );
+	}
+
+	public function getWeakConditionString() {
+		return implode( '', $this->weakConditions );
+	}
+
+	public function getCogentConditionString() {
+		return implode( '', $this->cogentConditions );
+	}
+
+}