Index-Assisted Hierarchical Computations in Main-Memory RDBMS.

We address the problem of expressing and evaluating computations on hierarchies represented as database tables. Engine support for such computations is very limited today, and so they are usually outsourced into stored procedures or client code. Recently, data model and SQL language extensions were proposed to conveniently represent and work with hierarchies. On that basis we introduce a concept of structural grouping to relational algebra, provide concise syntax to express a class of useful computations, and discuss algorithms to evaluate them efficiently by exploiting available indexing schemes. This extends the versatility of RDBMS towards a great many use cases dealing with hierarchical data.