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
/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.URLValue#getBaseParameterName <em>Base Parameter Name</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Base Parameter Name</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.URLValue#getBaseParameterName()
	 * @see #getURLValue()
	 * @generated
	 */
	EAttribute getURLValue_BaseParameterName( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.URLValue#getValueParameterName <em>Value Parameter Name</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Value Parameter Name</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.URLValue#getValueParameterName()
	 * @see #getURLValue()
	 * @generated
	 */
	EAttribute getURLValue_ValueParameterName( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.URLValue#getSeriesParameterName <em>Series Parameter Name</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Series Parameter Name</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.URLValue#getSeriesParameterName()
	 * @see #getURLValue()
	 * @generated
	 */
	EAttribute getURLValue_SeriesParameterName( );
	/**
	 * Returns the meta object for enum '{@link org.eclipse.birt.chart.model.attribute.ActionType <em>Action Type</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->