Creating a New Data Model from an Existing Workflow Data Model
This section describes how to create a new data model object based on the Workflow data model. The new data model enables you to create a Workflow service for specific Workflow tasks.
For information on how to create a new data model based on an existing data model, refer to the Deriving a Data Model from an Existing Data Model section.
After creating the data model you must create a consumption model. For information on how to create a consumption model, refer to the Creating a Consumption Model section.
When performing the procedure described above, you must make the following changes to create the new data models using Workflow data:
In the Create Data Model dialog box, enter one of the following data model names in the Name field under the Existing Data Model section:
/IWCNT/OM_WF_DEC_TASK – for Workflow user decision tasks
/IWCNT/OM_WF_ACTIVITY_TASK – for Workflow activity tasks
After the new data model has been created, add the relevant SAP Gateway data model that represents the Business Object using the RELATED_OBJECT collection.
Choosing the 
Generate STC class flag generates only the STC class and customizes the binding between the GSDO type and the STC class.
It also places the GSDO type created in the LOCAL GSDO Group.
You must add the Workflow GSI implementation manually.
Go to transaction SPRO.
Choose SAP Reference IMG.
Select
SAP Customizing Implementation Guide 
SAP NetWeaver SAP Gateway Former Development Former Generic Channel Development Generic Service Data Object (GSDO) GSDO Types & GSDO Contexts & GSI Implementations 
.Choose Execute.
In the GSDO table, select the new GSDO type you created.
Double-click GSI Implementation.
In the GSI Implementation table, under the Class/Interface column enter the following GSI class /IWCNT/CL_WF_GEN_TASK_BSO