conversion between DB and computational data

**Is your feature request related to a problem? Please describe.**
The service layer introduced data formats for influence diagram nodes and structure (ID and DT) which are better suited for computation than the data models used by the database.
Conversion between these formats had been implemented but are difficult to maintain due to changes in the data models and logic of the API's.

**Describe the solution you'd like**
An updated conversion between data models and computational formats.