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In this paper we discuss OLAF, a tracing tool that we have developed which enables the active database designer to watch the flow of events and rules through our Active Database system (GOAD). We shall show how we use active rules to halt the execution of active components that we wish to trace, and demonstrate how our emphasis on generality of design enables us to trace each type of active component (i.e. primitive events, composite events, rules etc.) without making any additional changes to the tracer. We shall discuss the OLAF tracer itself, showing the facilities it provides and how it is integrated with the rest of the GOAD toolset.

In this paper we introduce GOAD - an active database we have developed on top of GemStone - concentrating upon the implementation of our debugger prototype. We show how we extended the standard debugger provided with the GemStone-Smalltalk Interface to cope with the added complexity which the active parts of our system present. These extensions provide the means to trace the execution of rule code in the same straight-forward manner as standard class code. In addition we show how the GOAD visibility-toggling mechanism can be used by the debugger to provide different representations of an active application which are tailored to the needs of different types of users. We give an example of how, in conjunction with more abstract, graphical tools, we can use our debugger to help deal with errors in the functioning of the rule base. We conclude by evaluating the usefulness of our tool and the suitability of Smalltalk and GemStone as an underlying system for the development of tools such as the one we describe.

We discuss the design and implementation of an active object-oriented database built upon Gemstone, and an associated debugger. We concentrate upon the issue of visibility of ‘wrapping’ code, explaining why it is desirable for users of our system to be able to access and debug the code in both its ‘raw’ form and with the wrapping code hidden.

We discuss the implementation of GOAD (Gemstone Object-oriented Active Database), an active object-oriented database built on top of GemStone. This system has been developed with the specific aim of supporting interface tools for the creation and maintenance of rule bases, and we give particular attention to explaining how GOAD is designed to meet this aim. We show how objects, classes and metaclasses can support a three level event model which integrates with the underlying system in an ‘open’ manner. Moreover, by providing a uniform interface to these different objects, we are providing support for the implementation of more generic tools. We discuss the design of the system and how we gather inherited rules at run-time in an efficient manner. We explain the problems that arise as a result of our desired mode of implementation and how they were circumvented. Finally we discuss our future work and specifically how we plan to implement tools for the easier creation of rule bases.