public function writeWorkbookRelationships(PHPExcel $pPHPExcel = null)
	{
		// Create XML writer
		$objWriter = null;
		if ($this->getParentWriter()->getUseDiskCaching()) {
			$objWriter = new PHPExcel_Shared_XMLWriter(PHPExcel_Shared_XMLWriter::STORAGE_DISK, $this->getParentWriter()->getDiskCachingDirectory());
		} else {
			$objWriter = new PHPExcel_Shared_XMLWriter(PHPExcel_Shared_XMLWriter::STORAGE_MEMORY);
		}

		// XML header
		$objWriter->startDocument('1.0','UTF-8','yes');

		// Relationships
		$objWriter->startElement('Relationships');
		$objWriter->writeAttribute('xmlns', 'http://schemas.openxmlformats.org/package/2006/relationships');

			// Relationship styles.xml
			$this->_writeRelationship(
				$objWriter,
				1,
				'http://schemas.openxmlformats.org/officeDocument/2006/relationships/styles',
				'styles.xml'
			);

			// Relationship theme/theme1.xml
			$this->_writeRelationship(
				$objWriter,
				2,
				'http://schemas.openxmlformats.org/officeDocument/2006/relationships/theme',
				'theme/theme1.xml'
			);

			// Relationship sharedStrings.xml
			$this->_writeRelationship(
				$objWriter,
				3,
				'http://schemas.openxmlformats.org/officeDocument/2006/relationships/sharedStrings',
				'sharedStrings.xml'
			);

			// Relationships with sheets
			$sheetCount = $pPHPExcel->getSheetCount();
			for ($i = 0; $i < $sheetCount; ++$i) {
				$this->_writeRelationship(
					$objWriter,
					($i + 1 + 3),
					'http://schemas.openxmlformats.org/officeDocument/2006/relationships/worksheet',
					'worksheets/sheet' . ($i + 1) . '.xml'
				);
			}

		$objWriter->endElement();

		// Return
		return $objWriter->getData();
	}