We present an efficient algorithm (UWEP) for updating large itemsets when new transactions are added to the set of old transactions.UWEP employs a dynamic lookahead strategy in updating the existing large itemsets by detecting and removing those that will no longer remain large after the contribution of the new set of transactions.It differs from the other update algorithms by scanning the existing database at most once and the new database exactly once.Moreover, it generates and counts the minimum number of candidates in the new database.The experiments on synthetic data show that UWEP outperforms the existing algorithms in terms of the candidates generated and counted.

A formal object-oriented query model is described in terms of an object algebra. Both the structure and the behavior of objects are handled. An operand and the output from a query in the object algebra are defined to have a pair of sets, i.e. a set of objects and a set of message expressions, where a message expression is a valid sequence of messages. The closure property is therefore maintained in a natural way. In addition, it is proven that the output from a query has the characteristics of a class; hence, the inheritance relationship between the operand and the output from a query is derived.>

The authors propose a graphical query language, Time-by-Example (TBE), which has suitable constructs for interacting with historical relational databases in a natural way. TBE is user-friendly. It follows the graphical, two-dimensional approach of such previous languages as Query-by-Example (QBE), Aggregation-by-Example (ABE), and Summary-Table-by-Example (STBE). TBE also uses the hierarchical window (subquery) concept of ABE and STBE. TBE manipulates triple-valued (set-triple-valued) attributes and historical relations. Set-theoretic expressions are followed to deal with time intervals. The BNF specification for TBE is given.>