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
* <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Prefix</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.NumberFormatSpecifier#getPrefix()
	 * @see #getNumberFormatSpecifier()
	 * @generated
	 */
	EAttribute getNumberFormatSpecifier_Prefix( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.NumberFormatSpecifier#getSuffix <em>Suffix</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Suffix</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.NumberFormatSpecifier#getSuffix()
	 * @see #getNumberFormatSpecifier()
	 * @generated
	 */
	EAttribute getNumberFormatSpecifier_Suffix( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.NumberFormatSpecifier#getMultiplier <em>Multiplier</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Multiplier</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.NumberFormatSpecifier#getMultiplier()
	 * @see #getNumberFormatSpecifier()
	 * @generated
	 */
	EAttribute getNumberFormatSpecifier_Multiplier( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.NumberFormatSpecifier#getFractionDigits <em>Fraction Digits</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Fraction Digits</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.NumberFormatSpecifier#getFractionDigits()