How to provide ODATA service for sth like Select Option in a Web application?

Hi Experts,

Scenaio:

In UI5 application, We want to create something like search help for a single field. For exmaple, A button next to field SalesOrder ID triggers a search help with search criterias Sales Group, Sales Offices and so on. This is just like the classic ABAP dynpro field.

Need suggestion in SAP GW service generation:

• For the GW, how can I create a service which provide enough information to outside world?
• Is Annotation related in this scenario?
• Is there any document or step by step about this?

Thanks in advance.

Cain Sun