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System Lines - represent the business system family (e.g., ERP, CAR, CRM, etc.) based on functional distinctions. For example, in a typical small-scale ECC to S/4HANA migration project, the "ECC" and "S/4HANA" would be the two separate System Lines in Int4 configurations. It's worth noting that System Lines do not cover the integration platforms.
Environments - represent the various environments in the system landscape, typically "Development", "Test" and "Production". It's important to note that there could be only one integration platform instance in each technology assigned to an Environment. For example, in case of an upgrade project, e.g. PO 7.4 to PO 7.5, we would need typically twice as much environments: "Development74", "Test74" "Production74", "Development75", "Test75" and "Production75". It will not be the case if the integration platforms are based on different technologies.
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Automation Objects
Int4 Suite is built around the concept of Automation Objects - entities that contain configuration for each test execution step. Automation Objects define the interface under test, test conditions, and necessary data manipulation employing a Variable concept. Automation Objects can also point to other objects (UI scripts, database validation definitions, and more - as documented).
Read more about them in the dedicated section of this manual: Automation Objects
Test cases
A test case is a basic entry representing data for single test execution. The test case execution happens in the context of the assigned Automation Object in a specific Environment. System Line information is read from the Automation Object and can drive additional validation steps, specifically the Database Validation.
Test creators can link test cases into scenarios. It enables testing of complex, multiple-step flows, for example, the Order-To-Cash process.
Read more about test cases and scenarios in the manual: Test Cases and Testing scenarios and flows