Bug 104986 Backgound image uses an absolute path
Currently Chart uses an absolute path to indicate a backgournd image, that may cause the design unusable on other environments. Expected the background image can be definded in multiple ways like in report designer. e.g. URI(absolute path), File(relative path), Embedded Image(Encoded Image Data).
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/model/attribute/AttributePackage.java
/**
	 * The meta object id for the '{@link org.eclipse.birt.chart.model.attribute.impl.DateFormatSpecifierImpl <em>Date Format Specifier</em>}' class.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.impl.DateFormatSpecifierImpl
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getDateFormatSpecifier()
	 * @generated
	 */
	int DATE_FORMAT_SPECIFIER = 8;
	/**
	 * The feature id for the '<em><b>Type</b></em>' attribute. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */
	int DATE_FORMAT_SPECIFIER__TYPE = FORMAT_SPECIFIER_FEATURE_COUNT + 0;
	/**
	 * The feature id for the '<em><b>Detail</b></em>' attribute. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */
	int DATE_FORMAT_SPECIFIER__DETAIL = FORMAT_SPECIFIER_FEATURE_COUNT + 1;
	/**
	 * The number of structural features of the the '<em>Date Format Specifier</em>' class.
	 * <!-- begin-user-doc --> <!--
	 * end-user-doc -->
	 * @generated
	 * @ordered