Marek Rusinkiewicz

InfoSleuth: agent-based semantic integration of information in open and dynamic environments

The goal of the InfoSleuth project at MCC is to exploit and synthesize new technologies into a unified system that retrieves and processes information in an ever-changing network of information sources. InfoSleuth has its roots in the Carnot project at MCC, which specialized in integrating heterogeneous information bases. However, recent emerging technologies such as internetworking and the World Wide Web have significantly expanded the types, availability, and volume of data available to an information management system. Furthermore, in these new environments, there is no formal control over the registration of new information sources, and applications tend to be developed without complete knowledge of the resources that will be available when they are run. Federated database projects such as Carnot that do static data integration do not scale up and do not cope well with this ever-changing environment. On the other hand, recent Web technologies, based on keyword search engines, are scalable but, unlike federated databases, are incapable of accessing information based on concepts. In this experience paper, we describe the architecture, design, and implementation of a working version of InfoSleuth. We show how InfoSleuth integrates new technological developments such as agent technology, domain ontologies, brokerage, and internet computing, in support of mediated interoperation of data and services in a dynamic and open environment. We demonstrate the use of information brokering and domain ontologies as key elements for scalability.

On serializability of multidatabase transactions through forced local conflicts

A multidatabase transaction management mechanism called the optimistic ticket method (OTM) is introduced for enforcing global serializability. It permits the commitment of multidatabase transactions only if their relative serialization order is the same in all participating local database systems (LDBSs). OTM requires the LDBSs to guarantee only local serializability. The basic idea in OTM is to create direct conflicts between multidatabase transactions at each LDBS in order to determine the relative serialization order of their subtransactions. A refinement of OTM, called the implicit ticket method (ITM), is also introduced that uses implicit tickets and eliminates ticket conflicts but works only when the participating LDBSs use rigorous transaction scheduling mechanisms. ITM uses the local commitment order of each subtransaction to determine its implicit ticket value. It achieves global serializability by controlling the commitment (execution order) and thus the serialization order of multidatabase transactions. Both OTM and ITM do not violate the autonomy of the LDBSs and can be combined in a single comprehensive mechanism.<<ETX>>

On rigorous transaction scheduling

The class of transaction scheduling mechanisms in which the transaction serialization order can be determined by controlling their commitment order, is defined. This class of transaction management mechanisms is important, because it simplifies transaction management in a multidatabase system environment. The notion of analogous execution and serialization orders of transactions is defined and the concept of strongly recoverable and rigorous execution schedules is introduced. It is then proven that rigorous schedulers always produce analogous execution and serialization orders. It is shown that the systems using the rigorous scheduling can be naturally incorporated in hierarchical transaction management mechanisms. It is proven that several previously proposed multidatabase transaction management mechanisms guarantee global serializability only if all participating databases systems produce rigorous schedules. >

A graphical data manipulation language for an extended entity-relationship model

A user can formulate database queries and updates graphically, by manipulating schema diagrams. The authors based the graphical data manipulation interface on the entity-relationship (ER) model because of its widespread use and increasing popularity. They use an extended ER model incorporating various forms of generalization and specialization, including subset, union and partition relationships. They call their model the extended conceptual entity-relationship or ECER model. A comparison with other graphical entity-relationship interfaces is included.<<ETX>>

Specifying interdatabase dependencies in a multidatabase environment

The problem of interdatabase dependencies and the effect they have on applications updating interdependent data are addressed. A model that allows specifications of constraints among multiple databases in a declarative fashion is proposed. The separation of the constraints from the application programs facilitates the maintenance of data constraints and allows flexibility in their implementation. It allows investigation of various mechanisms for enforcing the constraints, independently of the application programs. By grouping the constraints together, it is possible to check their completeness and discover possible contradictions among them. The concepts of polytransactions, which use interdatabase dependencies to generate a series of related transactions that maintain mutual consistency among interrelated databases, is discussed.<<ETX>>

Using tickets to enforce the serializability of multidatabase transactions

To enforce global serializability in a multidatabase environment the multidatabase transaction manager must take into account the indirect (transitive) conflicts between multidatabase transactions caused by local transactions. Such conflicts are difficult to resolve because the behavior or even the existence of local transactions is not known to the multidatabase system. To overcome these difficulties, we propose to incorporate additional data manipulation operations in the subtransactions of each multidatabase transaction. We show that if these operations create direct conflicts between subtransactions at each participating local database system, indirect conflicts can be resolved even if the multidatabase system is not aware of their existence. Based on this approach, we introduce optimistic and conservative multidatabase transaction management methods that require the local database systems to ensure only local serializability. The proposed methods do not violate the autonomy of the local database systems and guarantee global serializability by preventing multidatabase transactions from being serialized in different ways at the participating database systems. Refinements of these methods are also proposed for multidatabase environments where the participating database systems allow schedules that are cascadeless or transactions have analogous execution and serialization orders. In particular, we show that forced local conflicts can be eliminated in rigorous local systems, local cascadelessness simplifies the design of a global scheduler, and that local strictness offers no significant advantages over cascadelessness. >

An approach to schema integration and query formulation in federated database systems

A language is introduced in which both schema integration and query formulation for federated database systems can be performed. The relational model is augmented with connectors that impose predicate conditions over attributes of relations either at the same or different sites. The relational model with connectors has a natural diagrammatic representation, and thus, the language has a graphical user interface. The theoretical foundation for the graphical language is algebraic. Bach algebraic operator maps a diagram (of relations with connectors) into another diagram, and every diagram represents a possible user query. Operators specifically designed to operate on incompatible schemas are introduced and formally defined. Possible domain incompatibilities are resolved by using extended abstract data types.

Management of interdependent data: specifying dependency and consistency requirements

Multiple databases that serve the needs of various application systems are considered. One of the significant problems in managing these databases is to maintain the related data items consistent to the required degree. This problem is frequently referred to as redundant data management. Since the term redundancy tends to imply that the data is unwanted or superfluous, the authors use the more general term management of interdependent data. Some preliminary ideas in this area are discussed. The problem of managing interdependent data is characterized, and some important types of interdatabase dependency are identified. The types of consistency requirements which can exist among the interdependent data are defined.<<ETX>>

Scheduling workflows by enforcing intertask dependencies

Workflows are composite activities that can be used to support and automate multisystem applications involving humans, heterogeneous databases and legacy systems. The traditional atomic transaction model, successful for centralized and homogeneous applications, is not suitable for supporting such workflows. Intertask dependencies, which are conditions involving events and dependencies among workflow tasks, are used to specify the coordination requirements among the workflow tasks and are a central component of most workflow models. They form a basis for developing a uniform formal framework for workflows, which is a key contribution of this work. In this paper, we formalize intertask dependencies using temporal logic. This involves event attributes, which are needed to determine whether a dependency is enforceable and to properly schedule events. Each dependency is represented internally as a finite state automaton that captures the computations that satisfy the given dependency. Sets of automata are combined into a scheduler that produces global computations satisfying all relevant dependencies, thus enacting the given workflow. This algorithm is rigorously proved correct; it has been implemented.

Report of the Workshop on Semantic Heterogeneity and Interpolation in multidatabase Systems

This report presents a review of the problems that were discussed during the Workshop on Semantic Heterogeneity and Interoperability in Multidatabase Systems. The workshop participants discussed the importance of interoperation in the U S WEST information processing environment and the progress that has been achieved in three major research areas: resolution of semantic heterogeneity among cooperating heterogeneous systems, transaction management in such environments, and software architecture for interoperation. The workshop provided researchers with necessary feedback from the industrial perspective and helped in identifying the major issues that need further research. The following problems concerning the applicability of the methods proposed for data processing in the heterogeneous, autonomous information systems have been identified: (i) many of the assumptions made in the research community are too restrictive to make the results directly applicable to existing environments; (ii) performance ramifications of various heterogeneous architectures need to be understood; (iii) the prototype systems need to be put to the test with real data, schemas, and transaction streams to verify their utility.