Shaul Dar

ASSET: a system for supporting extended transactions

Extended transaction models in databases were motivated by the needs of complex applications such as CAD and software engineering. Transactions in such applications have diverse needs, for example, they may be long lived and they may need to cooperate. We describe ASSET, a system for supporting extended transactions. ASSET consists of a set of transaction primitives that allow users to define custom transaction semantics to match the needs of specific applications. We show how the transaction primitives can be used to specify a variety of transaction models, including nested transactions, split transactions, and sagas. Application-specific transaction models with relaxed correctness criteria, and computations involving workflows, can also be specified using the primitives. We describe the implementation of the ASSET primitives in the context of the Ode database.

Direct transitive closure algorithms: design and performance evaluation

We present new algorithms for computing transitive closure of large database relations. Unlike iterative algorithms, such as the seminaive and logarithmic algorithms, the termination of our algorithms does not depend on the length of paths in the underlying graph (hence the name direct algorithms). Besides reachability computations, the proposed algorithms can also be used for solving path problems. We discuss issues related to the efficient implementation of these algorithms, and present experimental results that show the direct algorithms perform uniformly better than the iterative algorithms. A side benefit of this work is that we have proposed a new methodology for evaluating the performance of recursive queries.

A performance study of transitive closure algorithms

We present a comprehensive performance evaluation of transitive closure (reachability) algorithms for databases. The study is based upon careful implementations of the algorithms, measures page I/O, and covers algorithms for full transitive closure as well as partial transitive closure (finding all successors of each node in a set of given source nodes). We examine a wide range of acyclic graphs with varying density and “locality” of arcs in the graph. We also consider query parameters such as the selectivity of the query, and system parameters such as the buffer size and the page and successor list replacement policies. We show that significant cost tradeoffs exist between the algorithms in this spectrum and identify the factors that influence the performance of the algorithms. An important aspect of our work is that we measure a number of different cost metrics, giving us a good understanding of the predictive power of these metrics with respect to I/O cost. This is especially significant since metrics such as number of tuples generated or number of successor list operations have been widely used to compare transitive closure algorithms in the literature. Our results strongly suggest that these other metrics cannot be reliability used to predict I/O cost of transitive closure evaluation.

Queries in an Object-Oriented Graphical Interface

Abstract The graphical user interface OdeView for the Ode object-oriented database system allows users to perform complex operations against sets of objects. These include selection, projection, display, creation, deletion and update of objects, and the invocation of member functions (methods). OdeView utilizes type information for displaying objects and the relationships between objects, and for guiding the user in constructing syntactically correct query predicates. We present a formal model that underlies the OdeView display and query interface, illustrate the graphical query facilities through examples, and discuss our design decisions. We also describe our implementation, focusing on the usage of the Ode type catalog and the dynamic translation and execution of queries. As object database systems are becoming increasingly popular, we hope that the design and implementation details provided in this paper will benefit those interested in building graphical interfaces to database systems, particularly object-oriented database systems.

The O++ database programming language: implementation and experience

Ode, a database system and environment based on the object paradigm, is discussed. Ode is defined, queried and manipulated using the database programming language O++, which is based on C++. The O++ compiler translates O++ programs into C++ programs that contain calls to the Ode object manager. The implementation of O++, the Ode object manager, and the translation of the database facilities in O++ are described. The problems encountered in the implementation and their resolutions are reviewed.<<ETX>>

CQL++: A SQL for the Ode Object-Oriented DBMS

CQL++ is a declarative front end to the Ode object-oriented database. It combines a SQL-like syntax with the C++ class model. CQL++ provides facilities for defining classes, and for creating, querying, displaying, and updating objects. Classes and objects created using CQL++ can freely be intermixed with those created using O++, the primary programming language of Ode. CQL++ gives its users a relatively straightforward interface, by hiding from them such O++ details as object-ids, public and private members of objects, and the implementations (bodies) of member functions.

Research report. DataSpace: 3-D visualizations of large databases

DataSpace is a system for interactive 3-D visualization and analysis of large databases. DataSpace utilizes the display space by placing panels of information, possibly generated by different visualization applications, in a 3-D graph layout, and providing continuous navigation facilities. Selective rearrangements and transparency can be used to reduce occlusion or to compare or merge a set of images (e.g. line graphs or scatter plots) that are aligned and stacked in depth. A prototype system supporting the basic 3-D graphic operations (layout, zoom, rotation, translation, transparency) has been implemented. We provide several illustrative examples of DataSpace displays taken from the current system. We present the 3-D display paradigm, describe the query, layout and rendering steps required to create a display, and discuss some performance issues.

Composition of database relations

The authors argue for implementing composition as a primitive operation and present a single-sided composition algorithm that performs join protection and duplicate elimination as one unified operation. They report experimental results that show an operating region in which this algorithm outperforms composition by the standard method. This operating region is characterized by a join result many times larger than the source relations, and many duplicates after projection over the nonjoin attributes. This occurs, for example, in deductive databases when computing transitive closures of dense graphs.<<ETX>>

DTL's DataSpot: database exploration as easy as browsing the Web…

DTLs DataSpot is an advanced, programming-free tool that lets Web designers and database developers automatically publish their databases for Web browser access. DataSpot enables non-technical end users to explore a database using free-form plain language queries combined with hypertext navigation, in a fashion similar to using search engines such as Alta Vista to search text files on the Internet. DataSpot is based on a novel representation of data in the form of a schema-less semi-structured graph called a Web View. The DataSpot Publisher takes one or more possibly heterogeneous databases, predefined knowledge banks such as a thesaurus, and user-defined associations, and creates the Web View. The DataSpot Search Server, which connects to any standard HTTP server, performs searches and navigation against the Web View, generating dynamic HTML pages that are returned to the user. The presentation and navigation of answers are controlled by templates that can be modified by the data provider. The DataSpot product has been successfully deployed in diverse Internet and Intranet application areas, including electronic catalogs, yellow pages, classified ads, help desks and finance.