Abstract. When gathering information from multiple independent data sources, users will generally pose a sequence of queries to each source, combine (union) or cross-reference (join) the results in order to obtain the information they need. Furthermore, when gathering information, there is a fair bit of trial and error involved, where queries are recursively refined according to the results of a previous query in the sequence. From the point of view of an outside observer, the aim of such a sequence of queries may not be immediately obvious. We investigate the problem of isolating and characterizing subsequences representing coherent information retrieval goals out of a sequence of queries sent by a user to different data sources over a period of time. The problem has two sub-problems: segmenting the sequence into subsequences, each representing a discrete goal; and labeling each query in these subsequences according to how they contribute to the goal. We propose a method in which a discriminative probabilistic model (a Conditional Random Field) is trained with pre-labeled sequences. We have tested the accuracy with which such a model can infer labels and segmentation on novel sequences. Results show that the approach is very accurate (> 95 % accuracy) when there are no spurious queries in the sequence and moderately accurate even in the presence of substantial noise (∼70 % accuracy when 15 % of queries in the sequence are spurious).

multidatabase environment. In this paper, we propose a new multi-states query sampling method to develop local cost models for a dynamic environment. The system contention level at a dynamic local site is divided into a number of discrete contention states based on the costs of a probing query. To determine

their execution. Like traditional ECA rules, our ECA rule language has three parts: an event language, a condition language, and an action language. The event language provides a set of operators with a formal semantics for a multidatabase environment, and which allows a wide variety of composite events

cannot be directly applied to schema integration in a multidatabase environment. In this paper, the effects of execution orders, inconsistent data, and null values on the resultant semantics of natural outerjoins are explored. Because an arbitrary execution order of natural outerjoins may cause

A global view in a multidatabase system is defined as a query against base relations. When the global view is materialized, any update to the corresponding base relations needs to be propagated to the materialized view. This is known as view maintenance. Different maintenances of the same

Loosely coupled data integration among networked sources has become so ubiquitous over the recent years that many of the services and applications used daily are actually not monolithic information systems but rather collections of sources tied together. Instead of building centralized and large data sources (i.e., the Extract-

suggested so far, including database calibrating and query sampling, consider only a static multidatabase environment.

that are integrated into a multidatabase environment. One issue that has been relatively ignored is that of the architecture of multidatabase systems. We believe that a large multidatabase system spanning multiple organizations that are distributed over various geographically distant locations will not be developed

A multidatabase system (MDBS) is a facility that allows users access to data located in multiple autonomous database management systems (DBMSs). In such a system, global transactions are executed under the control of the MDBS. Independently, local transactions are executed under the control

by providing a single database illusion. A multidatabase environment supports two types of transac...