1. A computer-implemented method comprising: providing an in-memory database layer comprising a calculation model including a plurality of generic operators; providing in the in-memory database layer, a skeleton template set describing parallel execution of the plurality of generic operators, wherein the skeleton template set includes a skeleton template exhibiting a branch and bound structure; an in-memory database engine receiving a query; the in-memory database engine referencing the calculation model and the skeleton template to execute the query in parallel according to a skeleton instance including a custom operator having a parameter provided by the query; and displaying to a user, a result of executing the query on the in-memory database.