We describe the TIGUKAT objectbase management system that is under development at the Laboratory for Database Systems Research at the University of Alberta. TIGUKAT has a novel object model whose identifying characteristics include a purely behavioral semantics and a uniform approach to objects. Everything in the system, including types, classes, collections, behaviors, functions as well as meta-information, is a first-class object with well-defined behavior. In this way, the model abstracts everything, including traditional structural notions such as instance variables, method implementation and schema definition, into a uniform semantics of behaviors on objects. Our emphasis in this paper is on the object model, its implementation, the persistence model and the query language. We also (briefly) present other database management functions that are under development such as the query optimizer, the version control system and transaction manager.

We describe an extensible query optimizer for objectbase management systems. Since these systems are expected to serve data management needs of a wide range of application domains with possibly different query optimization requirements, extensibility is essential. Our work is conducted within the context of TIGUKAT, which is a uniform behavioral system that models every system component as a first-class object. Consistent with this philosophy, we model every component of the optimizer as a first-class object, providing ultimate extensibility. We describe the optimizer architecture and how the optimizer components are modeled as extensions of a uniform type system. 1 Introduction The early objectbase management systems (OBMSs) have been criticized [SRL + 90] for their lack of declarative query capabilities (both languages and optimizers). These facilities are common in the state-of-the-art relational database management systems (DBMSs).The newer commercial OBMSs and research prototy...

Query optimisers are critical to the efficiency of modern relational database systems. If a query optimiser chooses a poor query execution plan, the performance of the database system in answering the query can be very poor. In fact, the differences in cost between the least and most expensive query execution plans can be several orders of magnitude. On the other hand, it can be prohibitively expensive for the query optimiser to search exhaustively for the least-cost (strictly optimal) query execution plan. Most query optimisers, therefore, compromise by using a reasonably cheap search to obtain a reasonably cheap query execution plan. Accurate, but inexpensive, query size estimation is fundamental to the success of real query optimisers. A number of studies [Christodoulakis 1984; Ioannidis and Christodoulakis 1991, 1993] have demonstrated that optimisers can select very expensive query execution plans if they are forced to rely on poor or inaccurate query size estimates. This thesis will address the problem of how to obtain reliable and accurate query size estimation for the cost calculation of query execution plans.

As with other distributed database systems, it is important in an Active Object Oriented Knowledge Base Management System (AOOKBMS) to be able to execute distributed queries efficiently and cost effectively. In this paper, we show how this task is being tackled in an ongoing project at the University of Florida dealing with Virtual Enterprises (VE). This project uses an AOOKBMS to not only describe a common view of the VE's data and processing capabilities, but to also support distributed query optimization and processing. Through the use of wrappers this system allows the distributed execution of a query defined in an Object Query Language. It can be executed on heterogeneous systems that may include Object Oriented and Relational databases as well as non-database oriented systems. The results of this distributed processing is then combined and presented in a single uniform result, thus supporting the concept of a truly Virtual Enterprise. In this paper we cover how query optimization...