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diff --git a/www/wiki/extensions/SemanticMediaWiki/includes/dataitems/SMW_DataItem.php b/www/wiki/extensions/SemanticMediaWiki/includes/dataitems/SMW_DataItem.php
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+<?php
+
+use SMW\Options;
+
+/**
+ * This group contains all parts of SMW that relate to the processing of dataitems
+ * of various types.
+ *
+ * @defgroup SMWDataItems SMWDataItems
+ * @ingroup SMW
+ */
+
+/**
+ * Objects of this type represent all that is known about a certain piece of
+ * data that could act as the value of some property. Data items only represent
+ * the stored data, and are thus at the core of SMW's data model. Data items
+ * are always immutable, i.e. they must not be changed after creation (and this
+ * is mostly enforced by the API with some minor exceptions).
+ *
+ * The set of available data items is fixed and cannot be extended. These are
+ * the kinds of information that SMW can process. Their concrete use and
+ * handling might depend on the context in which they are used. In particular,
+ * property values may be influences by settings made for their property. This
+ * aspect, however, is not part of the data item API.
+ *
+ * @since 1.6
+ *
+ * @ingroup SMWDataItems
+ */
+abstract class SMWDataItem {
+
+	/// Data item ID that can be used to indicate that no data item class is appropriate
+	const TYPE_NOTYPE    = 0;
+	/// Data item ID for SMWDINumber
+	const TYPE_NUMBER    = 1;
+	/// Data item ID for SMWDIBlob
+	const TYPE_BLOB      = 2;
+	///  Data item ID for SMWDIBoolean
+	const TYPE_BOOLEAN   = 4;
+	///  Data item ID for SMWDIUri
+	const TYPE_URI       = 5;
+	///  Data item ID for SMWDITimePoint
+	const TYPE_TIME      = 6;
+	///  Data item ID for SMWDIGeoCoord
+	const TYPE_GEO       = 7;
+	///  Data item ID for SMWDIContainer
+	const TYPE_CONTAINER = 8;
+	///  Data item ID for SMWDIWikiPage
+	const TYPE_WIKIPAGE  = 9;
+	///  Data item ID for SMWDIConcept
+	const TYPE_CONCEPT   = 10;
+	///  Data item ID for SMWDIProperty
+	const TYPE_PROPERTY  = 11;
+	///  Data item ID for SMWDIError
+	const TYPE_ERROR     = 12;
+
+	/**
+	 * @var Options
+	 */
+	private $options = null;
+
+	/**
+	 * Convenience method that returns a constant that defines the concrete
+	 * class that implements this data item. Used to switch when processing
+	 * data items.
+	 * @return integer that specifies the basic type of data item
+	 */
+	abstract public function getDIType();
+
+	/**
+	 * Return a value that can be used for sorting data of this type.
+	 * If the data is of a numerical type, the sorting must be done in
+	 * numerical order. If the data is a string, the data must be sorted
+	 * alphabetically.
+	 *
+	 * @note Every data item returns a sort key, even if there is no
+	 * natural linear order for the type. SMW must order listed data
+	 * in some way in any case. If there is a natural order (e.g. for
+	 * Booleans where false < true), then the sortkey must agree with
+	 * this order (e.g. for Booleans where false maps to 0, and true
+	 * maps to 1).
+	 *
+	 * @note Wiki pages are a special case in SMW. They are ordered by a
+	 * sortkey that is assigned to them as a property value. When pages are
+	 * sorted, this data should be used if possible.
+	 *
+	 * @return float|string
+	 */
+	abstract public function getSortKey();
+
+	/**
+	 * Method to compare two SMWDataItems
+	 * This should result true only if they are of the same DI type
+	 * and have the same internal value
+	 *
+	 * @since 1.8
+	 *
+	 * @param SMWDataItem $di
+	 * @return boolean
+	 */
+	abstract public function equals( SMWDataItem $di );
+
+	/**
+	 * Create a data item that represents the sortkey, i.e. either an
+	 * SMWDIBlob or an SMWDINumber. For efficiency, these subclasses
+	 * overwrite this method to return themselves.
+	 *
+	 * @return SMWDataItem
+	 */
+	public function getSortKeyDataItem() {
+		$sortKey = $this->getSortKey();
+
+		if ( is_numeric( $sortKey ) ) {
+			return new SMWDINumber( $sortKey );
+		}
+
+		return new SMWDIBlob( $sortKey );
+	}
+
+	/**
+	 * Get a UTF-8 encoded string serialization of this data item.
+	 * The serialisation should be concise and need not be pretty, but it
+	 * must allow unserialization. Each subclass of SMWDataItem implements
+	 * a static method doUnserialize() for this purpose.
+	 * @return string
+	 */
+	abstract public function getSerialization();
+
+	/**
+	 * Get a hash string for this data item. Might be overwritten in
+	 * subclasses to obtain shorter or more efficient hashes.
+	 *
+	 * @return string
+	 */
+	public function getHash() {
+		return $this->getSerialization();
+	}
+
+	/**
+	 * @since 2.1
+	 *
+	 * @return string
+	 */
+	public function __toString() {
+		return $this->getSerialization();
+	}
+
+	/**
+	 * Create a data item of the given dataitem ID based on the the
+	 * provided serialization string and (optional) typeid.
+	 *
+	 * @param integer $diType dataitem ID
+	 * @param string $serialization
+	 *
+	 * @return SMWDataItem
+	 */
+	public static function newFromSerialization( $diType, $serialization ) {
+		$diClass = self::getDataItemClassNameForId( $diType );
+		return call_user_func( [ $diClass, 'doUnserialize' ], $serialization );
+	}
+
+	/**
+	 * Gets the class name of the data item that has the provided type id.
+	 *
+	 * @param integer $diType Element of the SMWDataItem::TYPE_ enum
+	 *
+	 * @throws InvalidArgumentException
+	 *
+	 * @return string
+	 */
+	public static function getDataItemClassNameForId( $diType ) {
+		switch ( $diType ) {
+			case self::TYPE_NUMBER:
+				return SMWDINumber::class;
+			case self::TYPE_BLOB:
+				return SMWDIBlob::class;
+			case self::TYPE_BOOLEAN:
+				return SMWDIBoolean::class;
+			case self::TYPE_URI:
+				return SMWDIUri::class;
+			case self::TYPE_TIME:
+				return SMWDITime::class;
+			case self::TYPE_GEO:
+				return SMWDIGeoCoord::class;
+			case self::TYPE_CONTAINER:
+				return SMWDIContainer::class;
+			case self::TYPE_WIKIPAGE:
+				return SMWDIWikiPage::class;
+			case self::TYPE_CONCEPT:
+				return SMWDIConcept::class;
+			case self::TYPE_PROPERTY:
+				return SMWDIProperty::class;
+			case self::TYPE_ERROR:
+				return SMWDIError::class;
+			case self::TYPE_NOTYPE: default:
+				throw new InvalidArgumentException( "The value \"$diType\" is not a valid dataitem ID." );
+		}
+	}
+
+	/**
+	 * @since 2.5
+	 *
+	 * @param string $key
+	 * @param string $value
+	 */
+	public function setOption( $key, $value ) {
+
+		if ( !$this->options instanceof Options ) {
+			$this->options = new Options();
+		}
+
+		$this->options->set( $key, $value );
+	}
+
+	/**
+	 * @since 2.5
+	 *
+	 * @param string $key
+	 * @param string|null $default
+	 *
+	 * @return mixed
+	 */
+	public function getOption( $key, $default = null ) {
+
+		if ( !$this->options instanceof Options ) {
+			$this->options = new Options();
+		}
+
+		if ( $this->options->has( $key ) ) {
+			return $this->options->get( $key );
+		}
+
+		return $default;
+	}
+
+}