In the URL of your service you can use the origin segment parameter o to expose the system alias. However, there can be different system aliases for one backend system if you use multiple origin composition (MOC). With multiple origin composition you can have access to several backend systems to retrieve data and might not necessarily want to use system aliases but instead use a combination of system ID and client. If you also want to create OData requests you might not have information on any SAP Gateway system alias. Therefore, SAP Gateway also supports OData requests with a combination of system ID and client as backend origin.
In addition, you might wish to refrain from thus exposing the system name of your SAP Gateway system in the URL of your service for security reasons. In this case, instead of the system name you can also use the system ID (SID) together with the corresponding client.
/sap/opu/odata/IWBEP/TEA_TEST_APPLICATION;o=XYZ_999/Teams
/sap/opu/odata/IWBEP/TEA_TEST_APPLICATION;o=sid(XYZ.999)/Teams
For each system alias you need to enter also a system ID and a client, if this has not yet been configured already. For more information, see Creating the SAP System Alias for Applications.