## WaterfallChartOLAPDataModel: Basic Requirements

The main responsibility of a WaterfallChartOLAPDataModel is to map data measures from an OLAP data structure to variable roles in a waterfall chart.

In your code, you can explicitly select measures in the OLAP data, or allow the component's OLAP data model to select measures by default.

A WaterfallChart's primary variable roles are

CategoryVariable
  Specifies a classification variable whose values determine the number and arrangement of bars in the chart. A WaterfallChartOLAPDataModel maps this role to the first measure in the OLAP structure.
ResponseVariable
  Specifies an analysis variable whose values determine the height of each bar. A WaterfallChartOLAPDataModel maps this role to the second measure in the OLAP structure.

To access OLAP data for a graph, you must know the name of the OLAP host server and connect to that server with a valid username and password. To use the OLAP data in a WaterfallChart, you must

- create an OLAPDataSet, either from the result set of a query that is executed on an OLAP provider or from the metadata that has been mapped to the OLAP data
- assign the OLAPDataSet to a WaterfallChartOLAPDataModel
- assign the WaterfallChartOLAPDataModel to a WaterfallChart.

The following code fragment generates a waterfall chart that plots actual sums against predicted sums for selected products, years, and countries.

    // Create strings to store an SQL query, the OLAP server name,
    // and the connection port.
       String OLAP_QUERY="SELECT "
                       + "{[PRODUCTLINE].[PRODUCT].MEMBERS} ON COLUMNS,"
                       + "CROSSJOIN({[TIME].[YEAR].MEMBERS},"
                       + "{[Measures].[ACTUAL_SUM],[Measures].[PREDICT_SUM]}) ON ROWS "
                       + "FROM MYOLAPCUBE";   // specify a valid OLAP data source
       String OLAP_SERVER="myOlapServer.com"; // use a valid server name
       int OLAP_PORT=8800;                    // use a valid port

    // Create a WaterfallChartOLAPDataModel from an OLAPDataSet.
       WaterfallChartOLAPDataModel olapDataModel = null;
       try {
            // OLAPDataSet arguments: host, port, username, pwd, query
               olapDataModel=new WaterfallChartOLAPDataModel(
               new OLAPDataSet(OLAP_SERVER, OLAP_PORT, "myUsername", "myPwd",
                               OLAP_QUERY));
           } catch (Exception ex) { ex.printStackTrace(); }

    // Create a WaterfallChart that uses the WaterfallChartOLAPDataModel as its data model
       WaterfallChart waterfallChart=new WaterfallChart();
       waterfallChart.setDataModel(olapDataModel);