Managed XML property

Hi,

we are setting up a local installation of OpenBIS and we love it. Thanks for your work!

While creating object types in the new admin interface, we noticed that we need a property type that stores an arbitrary number of tuples combining objects or strings with amounts, e.g.:
Material 1: 5g
Material 2: 100g
Material 3: 20g

Datatype-wise this might be realized via an XML property with the schema

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="Tuples">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="Tuple" maxOccurs="unbounded">
          <xs:complexType>
            <xs:sequence>
              <xs:element name="Material" type="xs:string"/>
              <xs:element name="Amount" type="xs:float"/>
            </xs:sequence>
          </xs:complexType>
        </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

However, manually entering XML to the field like this seems inconvenient:

<Tuples>
  <Tuple>
    <Material>Material 1</Material>
    <Amount>5</Amount>
  </Tuple>
  ...
</Tuples>

Ideally, we want a dropdown menu for the objects filtered by object type and a real number next to it with a plus button to add more lines of such tuples. I tried implementing it as a managed property, but find only seemingly outdated information about it.

Could you point me towards the right direction for implementing such a feature? Are there alternatives to it?

Thank you for any answer!
Nils