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Follow the instructions in Exposing a Datasource as a Data Service /wiki/spaces/EI6xx/pages/49614498 and when you get to the Add New Data Source screen, select Carbon Data Source as the data source type. You get a drop-down list from which an existing Carbon data source can be selected as shown below.
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Also, see the samples in Data Integration Samples/wiki/spaces/EI6xx/pages/49616348.