The best way to integrate with SAP ERP

Hello SAP Community.

I would like to know what methods exist to expose access to my SAP OnPremise (ERP) system from any other SAP or non-SAP system and interact with it over a LAN or WAN. The goal is to be able to access the data in the database, perform operations and store the result. It is worth clarifying that I want most of the development to be in the external system and not in the SAP OnPremise system. The SAP OnPremise system should only allow access to its database tables and the external system takes care of accessing them.

I appreciate any help, advice or information you can give me in this regard.

Thank you!