Daco Harkes, Eelco Visser. IceDust 2: Derived Bidirectional Relations and Calculation Strategy Composition. In Peter Müller, editor, 31st European Conference on Object-Oriented Programming, ECOOP 2017, June 19-23, 2017, Barcelona, Spain. Volume 74 of LIPIcs, Schloss Dagstuhl - Leibniz-Zentrum fuer Informatik, 2017.
Derived values are values calculated from base values. They can be expressed with views in relational databases, or with expressions in incremental or reactive programming. However, relational views do not provide multiplicity bounds, and incremental and reactive programming require significant boilerplate code in order to encode bidirectional derived values. Moreover, the composition of various strategies for calculating derived values is either disallowed, or not checked for producing derived values which will be consistent with the derived values they depend upon. In this paper we present IceDust2, an extension of the declarative data modeling language IceDust with derived bidirectional relations with multiplicity bounds and support for statically checked composition of calculation strategies. Derived bidirectional relations, multiplicity bounds, and calculation strategies all influence runtime behavior of changes to data, leading to hundreds of possible behavior definitions. IceDust2 uses a product-line based code generator to avoid explicitly defining all possible combinations, making it easier to reason about correctness. The type system allows only sound composition of strategies and guarantees multiplicity bounds. Finally, our case studies validate the usability of IceDust2 in applications.