Suzanne W. Dietrich

Interconnection of distributed components: an overview of current middleware solutions

From design and manufacturing to electronic commerce, coordinating business activities in engineering applications requires accessing data and software from distributed sources. The Common Object Request Broker Architecture (CORBA) of the Object Management Group emerged in the 1990’s as a standard for access to distributed software components. Since that time, the standard has matured significantly, providing advanced features for event notification and transaction processing. At the same time, Javabased technology for distributed object computing has also emerged, from Remote Method Invocation to Enterprise JavaBeans, Jini Connection Technology, JavaSpaces, Java Messaging Service, and Java Transaction Service. Sorting through the options available for the use of such tools can be a difficult task. This paper provides an overview of CORBA and Java technology for distributed object computing. A comparison of these different technologies is presented, discussing the similarities and differences, as well as the way in which such tools can be used together for distributed access to the types of software and data components that are needed for the construction of distributed engineering applications. Future directions for the use of such tools are also identified.

WinRDBI: a Windows-based relational database educational tool

RDBI is an educational tool that provides students with the capability to test their understanding of the formal relational query languages (relational algebra, domain relational calculus and tuple relational calculus) and the industry standard query language SQL. Although RDBI is an integral part of the database management courses at a number of universities, it is unavailable to those universities that do not have a license for the software product in which RDBI is implemented. WinRDBI, a version of RDBI for Windows, removes this limitation by increasing the availability of the educational tool to a standard Windows platform. Another advantage of WinRDBI is its graphical user interface, providing the student with a more intuitive interface than the command line interface of RDBI. This paper describes the architecture and user interface of WinRDBI. The features of WinRDBI are also illustrated using nontrivial examples from a popular database text. Although formal relational query languages do not provide inherent support for aggregation, these examples illustrate how to write queries in the formal languages to support (a limited form of) counting and minimum/maximum queries.

Database theory in practice: learning from cooperative group projects

This paper describes the use of cooperative group learning concepts in support of an undergraduate database management course that emphasizes the theoretical and practical aspects of database application development. The course project is divided into three main phases, involving requirements analysis and conceptual design, relational database mapping and prototyping, and database system implementation using Microsoft Access. The project deliverables are designed so that students not only develop a database implementation, but also evaluate their design in terms of functional dependencies, normal forms, the lossless join property, and the dependency preservation property, thus establishing the need for sound database design principles. Students are required to actively participate in each phase, with students assuming different roles in each phase to allow them to experience different leadership responsibilities. As part of the grading process, students evaluate their own performance as well as the performance of others in the group. This paper describes our experience with the structure and administration of cooperative groups and provides a discussion of the lessons we have learned, including initial observations of the effectiveness of the approach.

Integrating Active and Deductive Rules

This paper describes how active and deductive rules can be integrated to form an expressive representation for declaring and reasoning about events and conditions. Specifically, this paper describes an extension and optimizations to the PF algorithm, which detects events, i.e. updates, that affect derived relations (or views), even when the derived relation is recursively defined. This capability improves the expressiveness of the event-condition-action (ECA) rules, which can then be used to detect more complex events and express conditions that reason with the updates to both stored and derived relations. The updates to the derived relations can be detected without having to materialize the derived relations. The PF algorithm can detect these updates when certain modifications to the definition of the derived relation are made. This approach has been implemented to form an event detector and condition evaluator for an active deductive database. These enhancements increase the sophistication of an active database since ECA rules can be defined that react to a larger scope of real-world situations.

CDOL: a comprehensive declarative object language

In this paper we present a rule-based database language known as CDOL (Comprehensive, Declarative Object Language) that is an integration of deductive, object-oriented and active database technology. CDOL provides sublanguages for the expression of derived data, constraints, updates and active rules. The rule-based query language of CDOL provides an expressive approach to extend the stored database with derived attributes and classes. The constraint sublanguage allows explicit declarative specification of integrity constraints as a basis for database consistency. The update sublanguage of CDOL enables ad-hoc declarative update requests, where updates are encapsulated in the methods associated with class definitions, thus conforming to traditional objectoriented design concepts. The active rule sublanguage provides active, user-transparent agents that support reactive behavior within CDOL applications. In particular, active rules can be used to supplement declarative updates to maintain database consistency with respect to the set of integrity constraints. Active rules in general are used to monitor the occurrence of specific events and to serve as alerters and triggers within a CDOL application. This paper presents the rule-based query language of CDOL and illustrates the manner in which the constraint, update and active rule sublanguages build on this declarative framework. The use of methods and transactions are also addressed, together with a discussion of the operational semantics of active rule processing.

An Implementation and Evaluation of the Refined Triggering Graph Method for Active Rule Termination Analysis

This paper describes the implementation of the Refined Triggering Graph (RTG) method for active rule termination analysis. The RTG method has been defined in the context of an active, deductive, object-oriented database language known as CDOL (Comprehensive, Declarative, Object Language). The RTG method studies the contents of rule pairs and rule cycles in a triggering graph and tests for: 1) the successful unification of one rules action with another rules triggering event, and 2) the satisfiability of active rule conditions, asking if it is possible for the condition of a triggered rule to evaluate to true in the context of the triggering rules condition. If the analysis can provably demonstrate that one rule cannot trigger another rule, the directed vector connecting the two rules in a basic triggering graph can be removed, thus refining the triggering graph. Two important aspects in the implementation of the method include the development of a satisfiability algorithm for CDOL conditions and conditions and the extension of the RTG method with knowledge of the rule execution semantics. The effectiveness of the approach within the context of the sample application is also addressed.

Monitoring data dependencies in concurrent process execution through delta-enabled grid services

This paper presents our results with monitoring data dependencies among concurrently executing, distributed processes that execute over grid services. The research has been conducted in the context of the DeltaGrid project, focusing on the development of a semantically robust execution environment for the composition of grid services. Delta-Enabled Grid Services (DEGS) are a foundational aspect of the DeltaGrid environment, extending grid services with the capability of recording incremental data changes, known as deltas. Deltas generated by DEGS are forwarded to a Process History Capture System (PHCS) that organises deltas from distributed sources into a global, time-sequenced schedule of data changes. The design and construction of DEGS is presented, along with the storage and indexing techniques for merging deltas from multiple DEGS to create a global schedule of data changes that can be analysed to determine how the failure and recovery of one process can potentially affect other data-dependent processes. The paper also summarises the performance results for the global history construction and retrieval process.

A practitioner's introduction to database performance benchmarks and measurements

Database performance benchmarks provide an important measure for the comparison of database managment systems. This paper provides an introduction to performance benchmarks for centralised databases. The introduction includes benchamrks for transaction processing, such as DebitCredit, TPC-A and TPC-B, and benchmarks for decision support, such as the Wisconsin benchmark and its extension by bull to a vendor benchmark, known as the Single-User Decision Support benchmark

Advanced database concepts for undergraduates: experience with teaching a second course

This paper describes the development of a second database course for undergraduates, preparing students for the advanced database concepts they will experience in industry. Assuming an introductory course on relational database systems as a prerequisite, the topics addressed in the course include object-oriented data modeling, object-oriented database systems, object-relational database systems, Web access to databases, and professionalism and ethics. We present our experience with teaching the course, elaborating on the topics and assignments. We also present feedback from students and industry partners as well as our own assessment of future course refinements.

Extension table built-ins for Prolog

The ET* algorithm is a complete evaluation strategy for Datalog programs, which are logic programs without function symbols. The ET* algorithm uses extension tables and depth‐first iterative deepening to provide the evaluation of pure function‐free logic programs as declarative specifications. Extension tables are a memo facility that the algorithm uses both to cut infinite derivation paths for complete evaluation and to optimise the evaluation of logic programs.