Active OODBMSs must provide efficient support for event detection, composition and rule execution. Previous experience of building active capabilities on top of existing closed OODBMSs has proven to be ineffective. We propose instead an active OODBMS architecture where event detection and rule support are tightly integrated with the rest of the core OODBMS functionality. After presenting an analysis of the requirements of active OODBMSs, we discuss the event set, rule execution modes and lifespan of the events supported in our architecture. We also discuss event composition coupling relative to transaction boundaries. Since building an active OODBMS ex nihilo is extremely expensive, we are building the REACH (REal-time ACtive Heterogeneous) OODBMS by extending Texas Instruments' Open OODB toolkit. Open OODB is particularly well-suited for our purposes because it is the first DBMS whose architecture closely resembles the active database paradigm. It provides low-level event detection and invokes appropriate DBMS functionality as actions. We describe the architecture of the event detection and composition mechanisms, and the rule-firing process of the REACH active OODBMS, and show how these mechanisms interplay with the Open OODB core mechanisms.>

Object-oriented database systems (OODBS), which aim at meeting the data modeling, performance, cooperative design, and version management requirements of next-generation applications, such as CAD, CAM, CASE, hypermedia, and expert systems, are discussed. Key features of OODBS are presented, a taxonomy of approaches is provided, and architectural and implementation issues, design alternatives, and tradeoffs are examined. A variety of OODB systems, both research prototypes and commercial systems, are summarized. Industry efforts to accelerate a consensus that can lead to standards in the OODB are discussed.>

The effect of the variation of parameters of system elements on the overall performance of a generic model of a hydraulic actuation system for a robot is investigated. Specifically, an examination is made of the effects on actuator performance of two issues: intrinsic compliance i.e. the physical compliance within the actuator itself, and independent control of the actuator valve areas (e.g. supply and return areas for hydraulic fluid chamber) versus control of actuator valves with fixed area relationships. Increasing intrinsic compliance in the actuator degrades response to controller commands but improves the ability of the actuator to tolerate disturbances. Independent control of valve areas provides better response to commands and better rejection of disturbances than control with valves that have fixed area relationships. The performance information provided by the model permits behavior-based design of hydraulic actuation systems.>

A specialized data flow graph, Database Flow Graph ( DBFG ) is introduced. DBFGs may be used for scheduling database operations, particularly in an MIMD database machine environment. A DBFG explicitly maintains intertransaction and intratransaction dependencies, and is constructed from the Transaction Flow Graphs (TFG) of active transactions. A TFG, in turn, is the generalization of a query tree used, for example, in DIRECT [15]. All DBFG schedules are serializable and deadlock free. Operations needed to create and maintain the DBFG structure as transactions are added or removed from the system are discussed. Simulation results show that DBFG scheduling performs as well as two-phase locking.

Fractal surfaces have recently been shown to be a useful model for generating images of terrain in computer graphicS. Unfortunately, the generation of fractal images is very costly in CPU time. A multiprocessor architecture is described which takes advantage of the parallelism inherent in fractals to speed the generation of images. The performance of the processing array is analyzed along with the suitability of implementation in VLSI.

A secure implementation for subkey database encryption is presented. Both Vertical and Horizontal access to the control encrypted date are defined and described. Communication protocols between user and system are also provided.

A new cryptosystem that is suitable for database encryption is presented. The system has the important property of having subkeys that allow the encryption and decryption of fields within a record. The system is based on the Chinese Remainder Theorem.

The related fields of privacy and security are examined. Privacy issues are discussed and topics in the security fields of cryptography, database inference and operating systems are re viewed.

Databases may be compromised by asking a set of queries which return only statistical information and making inferences about a specific entry from the results of the set of queries. We present methods of constructing the set of queries to compromise a database where all the queries in the set return the maximum of a set of k elements, or all queries return the mean of a set of k elements. In the case of the mean query, all elements involved will be compromised. We also consider bounds on the number of queries required to compromise the database.