The COMET Database Management System

The COMET DBMS (component-based embedded real-time database management system) is an experimental database platform. COMET is intended for resourceconstrained embedded vehicle control-systems. The complexity of modern vehicle control systems is rapidly increasing [1], and so is also the amount of data that needs to be handled and maintained. Thus, a need has emerged for a structured way of handling this data. A real-time database management system would fulfill this need by providing a higher level of abstraction of the data management. Different vehicular control-systems have different requirements, i.e., some might be static and non-preemptive while other might be much more flexible, allowing preemption. Many vehicular systems are distributed, but some are not. This puts different requirements on the database. The natural approach would then be to develop an in-house DBMS that fulfills the requirements of the application. However, implementing a real-time database management system, and getting it certified as a component in a vehicular system is not a small task. A different approach would be to develop a tailorable database management system that can be configured to meet different kind of requirements. COMET is, too a high degree, tailorable to meet different kinds of requirements, such as different task-models, architectures, temporal constraints, and resource constraints. To achieve this, COMET is designed using both a component-based and aspect-oriented approach. Component-based software development enables systems to be built by previously built components. Each component is responsible for a well-defined task. By selecting a set of components that meet the requirements of the application, a specialized database can be made. In COMET we have identified the following components, user-interface component, transaction management component, index management component, memory management component, lock management component, check pointing and recovery management. The tasks of each of these components are described in section 5. Aspect-oriented software development allows some concerns of the system to be separated into an aspect. We have identified a number of aspects in COMET. Some aspects, such as the concurrency control-aspect change the behavior of the system, while other, such as the temporal aspect, are used to describe non-functional properties of the system. Aspect-oriented software development is further described in section 2. The COMET concept currently consists of a set of components, a set of aspects, a DBMS architecture and a tool to calculate worst-case execution times. Future versions of COMET will contain, configuration tools, more components and aspects, as well as further analysis tools. In this report we describe the underlying concepts of COMET. The architecture of COMET, the individual components and aspects identified in COMET, as well as our component-model, RTCOM, and our design model ACCORD is furthermore described. Finally we describe the COMET BaseLine implementation, which is the first instance of COMET intended for a vehicle control-system described in [2].