Mizuho Iwaihara

Bottom-up evaluation of logic programs using binary decision diagrams

Binary decision diagram (BDD) is a data structure to manipulate Boolean functions and recognized as a powerful tool in the VLSI CAD area. We consider that compactness and efficient operations of BDDs can be utilized for storing temporary relations in bottom-up evaluation of logic queries. We show two methods of encoding relations into BDDs, called logarithmic encoding and linear encoding, define relational operations on BDDs and discuss optimizations in ordering BDD variables to construct memory and time efficient BDDs. Our experiments show that our BDD-based bottom-up evaluator has remarkable performance against traditional hash table-based methods for transitive closure queries on dense graphs.<<ETX>>

Supporting dynamic constraints for commerce negotiations

Negotiation between buyer and supplier parties is an important part of commerce activities. Complex conditions are exchanged during a negotiation. It is important to realize a database of such conditions and provide querying facilities in an advanced electronic marketplace. We introduce the notion of dynamic constraints to model such complex negotiation conditions, and propose a new query language, called the dynamic constraint algebra. The algebra can classify and match dynamic constraints based on properties. We also show algorithms for processing dynamic constraint algebra queries.

Adapting transactions to exceptional situations using structured messages

We concentrate on the property that the progression of collaborative work involves communication among participants, and we consider a flexible method for managing transactions utilizing structured messages. In the literature, advanced transaction models for collaborative work environments have been proposed. However, since the models treat work processes as a target of transactions, it is difficult to adapt to exceptions or dynamic reconfiguration of processes. In this paper, we consider examples of handling exceptions in an environment involving workflow processes and database transactions, utilizing structured messages. We use the message transaction model for specifying workflow processes and various advanced transactions.

Structured Message Management for Group Interaction

In a collaborative working environment, process automation is necessary in the sense that (a) to show a flow of work items to be done, which is particularly important for assisting complex human tasks, (b) to show current status of each task to other participants, such as announcing which task is completed or continuing. More advanced functionalities which current process automation systems lack are: (c) support for ad-hoc and/or unstructured tasks such as discussions, decision making, and (d) collaboration of different teams, in which participants may not share all the process information, especially when carrying out negotiations. These requirements are universal to any types of collaborative work environments.

Navigation and schema transformations for producing nested relations from networks

Efficient procedures for producing nested relations from networks are considered. Various types of nested relations are defined according to the interaction between the networks and nested relations schemas. Among these types, partitional normal form (PNF) and accordant nested relations are shown to be produced by an extended navigation, called touch information display (TID) navigation, which requires time proportional to the number of tuples in the relation. It is demonstrated that a network can effectively produce a variety of nested relations by navigation. The efficiency of production is classified according to the interaction between the schemas of networks and targets. Non-PNF and/or non-accordant targets are generated using duplicate depletion. On the other hand, PNF and accordant targets can be generated using only navigation, which requires linear time in the number of tuples in the relation. Furthermore, for the cases on non-PNF and non-accordant targets, the TID method exploits the existence of links, so that the size of the region of the subrelation upon which deletion of duplicated values should be performed is limited.<<ETX>>