public interface IntervalCategoryDataset extends CategoryDataset {

    /**
     * Returns the start value for the interval for a given series and category.
     *
     * @param series  the series (zero-based index).
     * @param category  the category (zero-based index).
     *
     * @return The start value (possibly <code>null</code>).
     *
     * @see #getEndValue(int, int)
     */
    public Number getStartValue(int series, int category);

    /**
     * Returns the start value for the interval for a given series and category.
     *
     * @param series  the series key.
     * @param category  the category key.
     *
     * @return The start value (possibly <code>null</code>).
     *
     * @see #getEndValue(Comparable, Comparable)
     */
    public Number getStartValue(Comparable series, Comparable category);

    /**
     * Returns the end value for the interval for a given series and category.
     *
     * @param series  the series (zero-based index).
     * @param category  the category (zero-based index).
     *
     * @return The end value (possibly <code>null</code>).
     *
     * @see #getStartValue(int, int)
     */
    public Number getEndValue(int series, int category);

    /**
     * Returns the end value for the interval for a given series and category.
     *
     * @param series  the series key.
     * @param category  the category key.
     *
     * @return The end value (possibly <code>null</code>).
     *
     * @see #getStartValue(Comparable, Comparable)
     */
    public Number getEndValue(Comparable series, Comparable category);