Set-valued attributes frequently occur in contexts like marketbasked analysis and stock market trends. Late research literature has mainly focused on set containment joins and data mining without considering simple queries on set valued attributes. In this paper we address superset, subset and equality queries and we propose a novel indexing scheme for answering them on set-valued attributes. The proposed index superimposes a trie-tree on top of an inverted file that indexes a relation with set-valued data. We show that we can efficiently answer the aforementioned queries by indexing only a subset of the most frequent of the items that occur in the indexed relation. Finally, we show through extensive experiments that our approach outperforms the state of the art mechanisms and scales gracefully as database size grows.

Abstract.As governments across the world provide more and more support to open data initiatives and web 2.0 channels for engaging citizens, researchers orient themselves towards future internet, wisdom of crowds and virtual world experiments. In this context, the domain of ICT for Governance and Policy Modelling has recently emerged to achieve better, participative, evidence-based and timely governance. This paper presents a taxonomy classifying the research themes, the research areas and the research sub-areas that challenge this domain in order to deal with its diversity and complexity. Taking into account advancements in research, policy and practice, the taxonomy brings together the open, linked data and visual analytics philosophy; the social media buzz taming collective wisdom in decision-making; and the future internet approaches around cloud computing, internet of things and internet of services, while embracing the collaborative policy modelling aspects and the safeguarding against misuse implications.