Genero Report Writer provides the option to expand a template dynamically at runtime. 
  You can create a program to add data sources and the associated mapping to a template at
      runtime. This method uses a report template (.4rt) and design-time APIs
      to provide the details about the schema, the schema root, the relationships, and the field
      mappings in order to output the report, bypassing any need for a report design document. While
      more complex to set up, the advantage is that changes to your template are reflected with each
      new run of the report.
        Genero Report Writer allows you to expand templates at runtime, thereby providing end
            users with generic reports. Generic reports typically present themselves to end users in
            the following three phases:
                - The user is prompted for information regarding the template to use and the
                    values to use (variables and placeholders). While all the same options as
                    sophisticated as the template assistant in the report designer  are available,
                    typically the following things will be simplified:
                        - You can't choose multiple different templates. If choices are given,
                            they are limited to styles that match the data source (e.g. don't offer
                            a grouped list when the data source doesn't have groups). 
 
                        - You won't be prompted for difficult placeholders, for example those that
                            require the construction of formulas (e.g. Total expressions), and will
                            only be prompted for simple values (e.g. the Title of the report).
 
                        - You must choose fields from a single list of fields. Therefore,
                            templates that offer more than one field lists will not be used.
 
                    
Note: Building the dialog in a generic way to avoid hard coding placeholder
                        and field lists requires software that can introspect schema files and
                            .4rt files. A library is provided for
                    that.
 
                - The information entered by the user is used to expand the template and generate
                    a .4rp file.
Note: Expanding the template can be done in one
                        of two ways: 
                            - By calling an existing library function.
 
                            - By invoking the GenerateReport executable provided with GRE.
 
                        
 
 
                - The data source is run using the generated .4rp file.
                        
Note: The data source is run with the .4rp via the
                        normal runtime API functions.