The two paradigms to identify records of preference in a multi-objective setting rely either on dominance (e.g., the skyline operator) or on a utility function defined over the records’ attributes (typically using a top- k query). Despite their proliferation, each has its own palpable drawbacks. Motivated by these drawbacks, we identify three hard requirements for practical decision support, namely, personalization, controllable output size, and flexibility in preference specification. With these requirements as a guide, we combine elements from both paradigms and propose two new operators, ORD and ORU . We present a suite of algorithms for their efficient processing, dedicating more technical effort to ORU , whose nature is inherently more challenging. Specifically, besides a sophisticated algorithm for ORD , we describe two exact methods for ORU and one approximate. We perform a qualitative study to demonstrate how our operators work and evaluate the performance of our algorithms against adaptations of previous work that mimic their output.

Top-k related queries in continuous preference space (e.g., k-shortlist preference query kSPR, uncertain top-k query UTK, output-size specified utility-based query ORU) have numerous applications but are expensive to process. Existing algorithms process each query via specialized optimizations, which are difficult to generalize. In this work, we propose a novel and general index structure T-LevelIndex, which can be used to process various queries in continuous preference space efficiently. We devise efficient approaches to build the T-LevelIndex by fully exploiting the properties of continuous preference space. We conduct extensive experimental studies on both real- and synthetic- benchmarks. The results show that (i) our proposed index building approaches have low costs in terms of both space and time, and (ii) T-LevelIndex significantly outperforms specialized solutions for processing a spectrum of queries in continuous preference space, and the speedup can be two to three orders of magnitude.

The two most common paradigms to identify records of preference in a multi-objective setting rely either on dominance (e.g., the skyline operator) or on a utility function defined over the records' attributes (typically, using a top-k query). Despite their proliferation, each of them has its own palpable drawbacks. Motivated by these drawbacks, we identify three hard requirements for practical decision support, namely, personalization, controllable output size, and flexibility in preference specification. With these requirements as a guide, we combine elements from both paradigms and propose two new operators, ORD and ORU. We perform a qualitative study to demonstrate how they work, and evaluate their performance against adaptations of previous work that mimic their output.