Abstract: A method and computer program for optimizing computation and data retrieval of join operations from a multi-node log-structure database system. The database system has one or more data tables each having a plurality of columns. A join index is created for one or more join key columns, with optionally one or more secondary columns, of one of the data tables. The join index is partitioned across at least one computing node, and each join index partition reproduces the log structure storage of the data table. The join index is maintained in a series of incremental operations by replicating the creation or deletion of data segments from the log structure storage of the data table to the join index partitions.

Abstract: A method, system and computer program product are disclosed for determining a shortest path between two nodes of a graph, where the graph is represented in one or more tables of a relational database as a plurality of records identifying edges between pairs of connected nodes in the graph. A request specifies a source node (or set of source nodes), a target node (or set of target nodes) and a maximum path length L. Each path length l, from 1 to L, is iteratively tested by first generating a query comprising a sequence of join operations for that path length, and secondly decomposing the join operations into a sequence of one or more tree-structured queries comprising semi-join operations. Each tree-structured query when executed as a sequence of semi-join operations will return either an empty result set, indicating that no shortest path exists at that path length, or a non-empty result set which identifies all edges at step k of each shortest path of length l, where 1?k?l.

Abstract: A computer-implemented method is disclosed for executing aggregate queries of composite relationships from an Entity-Relationship (ER) model which sources data from a plurality of heterogeneous and decentralised databases. The method comprises maintaining an ER model comprising a plurality of entities En for which data exists in one or more databases, and one or more relationships rn between those entities. An aggregate query is received relating to a composite relationship cr(r1, r2) involving entities E1, E2 and E3 wherein r1 is a relation between E1 and E2, and wherein r2 is a relation between E2 and E3. The computation of the aggregate query is optimized by selecting an aggregation strategy according to the relation between entities E1, E2 and E3, such that a single table aggregation strategy, a semi-join strategy or a join strategy is selected according to the relation between tables defining entities in the ER model.