There is a need to efficiently navigate on a large graph to find a certain piece of information by some structure constraints. Reachability query could be the main means for such a purpose and existing approaches studied an efficient primitive called reachability join. In this paper, we focus on processing the query containing multi reachability joins (R-joins). We studied the processing abilit...

We propose a radical approach to relational query processing that aims at automatically and consistently achieving a good performance on any memory hierarchy. We believe this automaticity and stableness of performance is at times more desirable than some peak performance achieved through careful tuning, especially because both database systems and hardware platforms are becoming increasingly co...

Recently, the database and AI research communities have paid increased attention to ontologies. The main motivating reason is that ontologies promise solutions for complex problems caused by the lack of a good understanding of the semantics of data in many cases. In particular, ontologies have extensively been used to overcome the interoperability problem during the integration of heterogeneous...

Innovative query interfaces to knowledge and database systems must go beyond simply returning the requested information. They must be capable of producing intentional answers when a description improves the understanding of an answer [Mot94], producing conditional answers when no one answer matches the conditions of a query, and using ontological information in processing a query. They should b...

The number of linked data sources available on the Web is growing at a rapid rate. Moreover, users are showing an interest for any framework that allows them to obtain answers, for a formulated query, accessing heterogeneous data sources without the need of explicitly specifying the sources to answer the query. Our proposal focus on that interest and its goal is to build a system capable of ans...

Query processing in databases can be divided into two steps: selecting an 'optimal' evaluation strategy, and executing it. We first present elementary nested loop and relational algebra algorithms for query execution and point out some opportunities for improving their performance. A survey of optimization strategies, structured in query transformation techniques and access planning methods, fo...

In obiect-oriented databases, relationships are generally maintained explicitly. The partial result of a retrieved object can be used to efficiently retrieve related objects. Instead of optimizing joins as in relational database systems, pointer chasing is optimized in object-oriented database systems. Further, semantics inherent in the object-oriented database, like superclass-subclass relatio...

Graph has great expressive power to describe the complex relationships among data objects, and there are large graph datasets available. In this paper, we focus ourselves on processing a primitive graph query. We call it reachability query. The reachability query, denoted A D, is to find all elements of a type D that are reachable from some elements in another type A. The problem is challenging...

Modern Internet applications often produce a large volume of user activity records. Data analysts are interested in cohort analysis, or finding unusual user behavioral trends, in these large tables of activity records. In a traditional database system, cohort analysis queries are both painful to specify and expensive to evaluate. We propose to extend database systems to support cohort analysis....

Speculation is an every day phenomenon whereby one acts in anticipation of particular conditions that are likely to hold in the future. Computer science research has seen many successfull applications of speculation: modern processors, for example, speculate on the run-time properties of a program and decide to pre-execute instructions accordingly. We draw inspiration from these techniques and ...