Peter M. Schwarz

ARIES: a transaction recovery method supporting fine-granularity locking and partial rollbacks using write-ahead logging

DB2<supscrpt>TM</supscrpt>, IMS, and Tandem<supscrpt>TM</supscrpt> systems. ARIES is applicable not only to database management systems but also to persistent object-oriented languages, recoverable file systems and transaction-based operating systems. ARIES has been implemented, to varying degrees, in IBMs OS/2<supscrpt>TM</supscrpt> Extended Edition Database Manager, DB2, Workstation Data Save Facility/VM, Starburst and QuickSilver, and in the University of Wisconsins EXODUS and Gamma database machine.

DiscoveryLink: a system for integrated access to life sciences data sources

Vast amounts of life sciences data reside today in specialized data sources, with specialized query processing capabilities. Data from one source often must be combined with data from other sources to give users the information they desire. There are database middleware systems that extract data from multiple sources in response to a single query. IBMs DiscoveryLink is one such system, targeted to applications from the life sciences industry. DiscoveryLink provides users with a virtual database to which they can pose arbitrarily complex queries, even though the actual data needed to answer the query may originate from several different sources, and none of those sources, by itself, is capable of answering the query. We describe the DiscoveryLink offering, focusing on two key elements, the wrapper architecture and the query optimizer, and illustrate how it can be used to integrate the access to life sciences data from heterogeneous data sources.

Synchronizing shared abstract types

Experimental data on transient errors from several digital computer systems is presented and analyzed. This is the first large scale public study on the statistical distribution of transient errors. The systems for which data has been collected are the DEC PDP-10 scries computers, the Cm* multiprocessor, and the C.vmp fault tolerant microprocessor. Statistical tests indicate that transient errors follow a decreasing hazard rate distribution. This is at variance with the standard assumption of constant hazard rates (exponential distribution) used in reliability modeling, and requires models of greater complexity for accurate results. Models of common fault tolerant redundant structures are developed using the Weibul! distribution, which has a time-varying hazard rate. Both analytical and simulation models arc used to analyze die differences between the reliabilities predicted by Weibull based transient error models and those predicted by exponential based models. The analysis indicates a significant difference between the models based on the exponential distribution and those based on the decreasing hazard rate Weibull distribution. Reliability differences ranging from -0.10 to +0.20 and factors greater than 2.0 in Mission Time Improvement for Weibull parameters equivalent to measured system behavior arc seen in the model results. System designers should be aware of these differences. Transient Error Reliability Models Based on Data Analysis

Aspects: extending objects to support multiple, independent roles

The type systems of most object-orientecl database syst ems ( 00 DBSS) descend from traditional object-oriented programming lan gna,ges. While these systems can capture many interesting relationships among entities, such as classification ancf snbtyping, they do not typically allow an object, to change type, and they only partially support the mode]ling of objects that have many types. However, such characteristics are particularly common among the very entities (e. g., people) that these systems are intended to model. We introduce aspects, a new mechanism designecf to meet, these modelling requirements within the framework of a strongly-typed 00DBS. An aspect extends an existing object with new state and new behavior while maintaining the same object identity. In addition to the modelling of roles, aspects have other interesting applications, such as encapsulating the result, of a query.

Garlic: a new flavor of federated query processing for DB2

In a large modern enterprise, information is almost inevitably distributed among several database management systems. Despite considerable attention from the research community, relatively few commercial systems have attempted to address this issue. This paper describes new technology that enables clients of IBMs DB2 Universal Database to access the data and specialized computational capabilities of a wide range of non-relational data sources. This technology, based on the Garlic prototype developed at the Almaden Research Center, complements and extends DB2s existing ability to federate relational data sources.The paper focuses on three topics. Firstly, we show how the DB2 catalogs are used as an extensible repository for the metadata needed to access remotely-stored information. Secondly, we describe how the Garlic approach to query planning, in which source-specific modules and the federated server cooperate to develop an optimized execution plan, has been realized in DB2. Lastly, we describe how DB2s query execution engine has been extended to support queries and functions that are evaluated remotely.

Querying multimedia data from multiple repositories by content: the Garlic project

We describe Garlic, an object-oriented multimedia middleware query system. Garlic enables existing data management components, such as a relational database or a full text search engine, to be integrated into an extensible information management system that presents a common interface and user access tools. We focus in this paper on how QBIC, an image retrieval system that provides content-based image queries, can be integrated into Garlic. This results in a system in which a single query can combine visual and nonvisual data using type-specific search techniques, enabling a new breed of multimedia applications

Support for Distributed Transactions in the TABS Prototype

The TABS prototype is an experimental facility that provides operating system-level support for distributed transactions that operate on shared abstract types. The facility is designed to simplify the construction of highly available and reliable distributed applications. This paper describes the TABS system model, the TABS prototypes structure, and certain aspects of its operation. The paper concludes with a discussion of the status of the project and a preliminary evaluation.

SQL and management of external data

In late 2000, work was completed on yet another part of the SQL standard [1], to which we introduced our readers in an earlier edition of this column [2].Although SQL database systems manage an enormous amount of data, it certainly has no monopoly on that task. Tremendous amounts of data remain in ordinary operating system files, in network and hierarchical databases, and in other repositories. The need to query and manipulate that data alongside SQL data continues to grow. Database system vendors have developed many approaches to providing such integrated access.In this (partly guested) article, SQLs new part, Management of External Data (SQL/MED), is explored to give readers a better notion of just how applications can use standard SQL to concurrently access their SQL data and their non-SQL data.

Transactions: a construct for reliable distributed computing

Transactions have proven to be a useful tool for constructing reliable database systems and are likely to be useful in many types of distributed systems. To exploit transactions in a general purpose distributed system, each node can execute a transaction kernel that provides services necessary to support transactions at higher system levels. The transaction model that the kernel supports must permit arbitrary operations on the wide collection of data types used by programmers. New techniques must be developed for specifying the synchronization and recovery properties of abstract types that are used in transactions. Existing mechanisms for synchronization, recovery, deadlock management and communication are often inadequate to implement these types efficiently, and they must be adapted or replaced.

CACL: efficient fine-grained protection for objects

CACL is a protection scheme for objects that offers a simple and flexible model of protection and has an efficient, software-only implementation. The model, based on Access Control Lists (ACLs) integrated with the type system, allows owners to control who may invoke which methods on which objects, permits cooperation between mutually suspicious principals, allows ownership of objects to be transferred safely, prevents unwanted propagation of authority between principals, and allows changes to the authorization information to take effect on the next method invocation. The implementation, based on the integration of Capabilities with method dispatch, avoids the overhead of access checking in the majority of invocations, at the cost of space for extra dispatch vectors. CACL offers a viable mechanism for finegrained protection in an object-oriented database system.