While standardization efforts for XML query languages have been progressing, researchers and users increasingly focus on the database technology that has to deliver on the new challenges that the abundance of XML documents poses to data management: validation, performance evaluation and optimization of XML query processors are the upcoming issues. Following a long tradition in database research, we provide a framework to assess the abilities of an XML database to cope with a broad range of different query types typically encountered in real-world scenarios.

We consider different methods of optimizing the classification process of terminological representation systems, and evaluate their effect on three different types of test data. Though these techniques can probably be found in many existing systems, until now there has been no coherent description of these techniques and their impact on the performance of a system. One goal of this paper is to make such a description available for future implementors of terminological systems. Building the optimizations that came off best into the kris system greatly enhanced its efficiency.

In the engineering and scientific marketplaces, the workstation-server model of computing is emerging as the standard of the 1990s. Implementing an object-oriented database system in this environment immediately presents the design choice of how to partition database functionality between the server and workstation processors. To better understand the alternatives to this fundamental design decision, we analyze three different workstation-server architectures, evaluating them both qualitatively and through benchmarking of prototypes. The three approaches are labeled object server, in which individual objects pass between the server and workstation, page server, in which a disk page is the unit of transport and the server buffers pages, and file server, where whole pages are transferred as well, but they are accessed directly by the workstation process via a remote file service (namely, NFS). We built prototypes of all three architectures, using a stripped-down version of the WiSS storage system as a starting point. To compare the performance of the prototypes, and to experiment with sensitivity to data placement and cache sizes, we developed our own object manager benchmark, the Altair Complex-Object Benchmark (ACOB). This benchmark supports experiments that vary both clustering (inter-object locality) and smearing (intra-object locality). The test suite of benchmarks includes queries for scanning the entire database and traversing and updating complex objects.

With standardization efforts of a query language for XML documents drawing to a close, researchers and users increasingly focus their attention on the database technology that has to deliver on the new challenges that the sheer amount of XML documents produced by applications pose to data management: validation, performance evaluation and optimization of XML query processors are the upcoming issues. Following a long tradition in database research, the XML Store Benchmark Project provides a framework to assess an XML database's abilities to cope with a broad spectrum of different queries, typically posed in real-world application scenarios. The benchmark is intended to help both implementors and users to compare XML databases independent of their own, specific application scenario.

Although object-oriented database systems offer advantages over relational or record-oriented database systems, such as modeling facilities for complex objects, they are criticized for poor performance and query capabilities on set-oriented applications. The unacceptable performance is due in part to the object-at-a-time processing typically used by object-oriented database systems. We believe that improved performance of object-oriented database systems depends partially on the efficient and selective retrieval of sets of complex objects from secondary storage. In this report, we present the method of complex object retrieval and assembly used in the Volcano query processing system and the Revelation project. We also present experimental results comparing set-oriented versus object-at-a-time complex object assembly. 1. Introduction Relational database management systems provide a simple and well-understood model of data. The simplicity and theory of the relational model result in eff...

Abstract. Work ow management is a ubiquitous task faced by many organizations, and entails the coordination of various activities. This coordination is increasingly carried out by software systems called workow management systems (WFMS). An important component ofmany WFMSs is a DBMS for keeping track ofwork ow activity. This DBMS maintains an audit trail, or event history, that records the results of each activity. Like other data, the event history can be indexed and queried, and views can be de ned on top of it. In addition, a WFMS must accommodate frequent work ow changes, which result from a rapidly evolving business environment. Since the database schema depends on the workow, the DBMS must also support dynamic schema evolution. These requirements are especially challenging in high-throughput WFMSs|i:e:, systems for managing high-volume, mission-critical work ows. Unfortunately, existing database benchmarks do not capture the combination of exibility and performance required by these systems. To address this issue,

A distributed object database stores objects persistently at servers. Applications run on client machines, fetching objects into a client-side cache of objects. If fetching and cache management are done in terms of objects, rather than fixed-size units such as pages, three problems must be solved: 1. which objects to prefetch, 2. how to translate, or swizzle, inter-object references when they are fetched from server to client, and 3. which objects to displace from the cache. This thesis reports the results of experiments to test various solutions to these problems. The experiments use the runtime system of the Thor distributed object database and benchmarks adapted from the Wisconsin OO7 benchmark suite. The thesis establishes the following points: 1. For plausible workloads involving some amount of object fetching, the prefetching policy is likely to have more impact on performance than swizzling policy or cache management policy. 2. A simple breadth-first prefetcher can have performa...

Multi-level transactions are a variant of open-nested transactions in which the subtransactions correspond to operations at different levels of a layered system architecture. They allow the exploitation of semantics of high-level operations to increase concurrency. As a consequence, undoing a transaction requires compensation of completed subtransactions. In addition, multi-level recovery methods must take into consideration that high-level operations are not necessarily atomic if multiple pages are updated in a single subtransaction. This article presents algorithms for multi-level transaction management that are implemented in the database kernel system (DASDBS). In particular, we show that multi-level recovery can be implemented in an efficient way. We discuss performance measurements using a synthetic benchmark for processing complex objects in a multi-user environment. We show that multi-level transaction management can be extended easily to cope with parallel subtransactions within a single transaction. Performance results are presented with varying degrees of inter- and intratransaction parallelism.

Large knowledge bases that are intended for applications such as CAD, corporate repositories or process control will have to be shared by multiple users. For these systems to scale up, to give acceptable performance and to exhibit consistent behavior, it is mandatory to synchronize user transactions using a concurrency control algorithm. The transactions in knowledge bases often access a large number of entities and perform complex inferences that may last for a long period of time. In such a situation, using conventional concurrency control methods, which require a transaction to hold its locks until it has acquired all the locks it will ever need, do not lead to good performance. This thesis examines the problem of concurrency control for such long transactions in a knowledge base setting. Using a directed graph as a general model of a knowledge base, we develop an algorithm, called the Dynamic Directed Graph (DDG) policy, that allows release of locks by a transaction before it has ...

OO7 has been widely used by developers to benchmark commercial Object Oriented Data Bases (OODB) and by researchers as a realistic workload for experimenting with persistent object systems (POS). These uses of OO7 levy very different requirements; the former needs an application benchmark while the latter needs a system benchmark. This paper describes our experiences with using OO7 both as an application benchmark and a system benchmark. Based on this experience, we outline a framework of the features needed for both kinds of benchmarks. We evaluated OO7 using this framework and found it unsuitable for these tasks. 1 Introduction The construction of many large applications that manipulate complex data structures has motivated significant academic research and industrial development of Object Oriented Databases (OODB) and Persistent Object Stores (POS). In terms of the feature set supported, we will consider an OODB to be a superset of a POS. Both builders and users of such systems wou...