To construct a URL you can get filter format from the WHERE condition of the VQL command.
For example, if you have a register and want to filter it using just one value you can simply use the where clause, (register_field).f1=value
The URL in this case can be: http://acme:9090/denodo-restfulws/.../views/view1?$filter=(register_field).f1=value
If you want to filter using all of the register values you can use the WHERE clause format register_field = ROW('value1', 'value2', ‘value3’))
The URL, in this case, can be like this:
If you have a nested register register_field(value1, value2, register(reg_value1, reg_value2)) in your view you can access the view using the where condition like register_field=ROW(‘value1’, ‘value2’, ROW(‘reg_value1’, reg_value2))
The URL for this can be
http://acme:9090/denodo-restfulws/.../views/view1?$filter=register_field=ROW(‘value1’, ‘value2’, ROW(‘reg_value1’, reg_value2))
To have some more examples you can refer to this document below
Hope this helps!