Incremental updates to multiple inheritance hierarchies are becoming more prevalent with the increasing number of persistent applications supporting complex objects, making the efficient computation of lattice operations such as greatest lower bound (GLB), least upper bound (LUB), and subsumption more and more important. General techniques for the compact encoding of a hierarchy are presented. One such method is to plunge the given ordering into a boolean lattice of binary words, leading to an almost constant-time complexity of the lattice operations. The method is based on an inverted version of the encoding of Ait-Kaci et al. to allow incremental update. Simple grouping is used to reduce the code space while keeping the lattice operations efficient. Comparisons are made to an incremental version of the range compression scheme of Agrawal et al., where each class is assigned an interval, and relationships are based on containment in the interval. The result is two encoding methods which have their relative merits. The former being better for smaller, more structured hierarchies, and the latter for larger, less organized hierarchies.

Presents a graphical technique for semantic query optimization for ODMG-93 compliant databases. The OQL object query is represented as a graph based on the information contained in the ODL object schema. The graph reflects the constraints on possible objects satisfying the query. Vertices represent objects, which may be members of interfaces, ranges of values, constant values, objects returned by subqueries, object collections (count, sum, etc.) or constructs (sets, lists, etc.). Key constraints and inverse relationships contained in the schema are used to perform join elimination, join simplification and scan reduction via graph transformations. A marking scheme on the graph is used to perform subquery-to-join transformations and the detection of unnecessary duplication elimination. We argue that our approach generalizes previous research on object-based query optimization by providing a more natural representation of the query, allowing simpler, more intuitive transformations and leading to more efficient evaluation plans.

Interactive design of object-oriented schema requires a tool that permits fine-grained, incremental capture of semantic intent in the form of atomic assertions and provides user feedback reflecting the consequences of the design. The paper describes a design tool that includes a graphical interface for schema entry and feedback, a conceptual reasoner to perform the deductions, and a schema generator that outputs the data definition language of choice. The graphical interface is concerned with issues of object placement, line crossing, and object focus. The conceptual reasoner constructs a representation of the schema as a constraint network graph, based on the concept of congruence closure. The schema generator produces data definitions based on the deductions of the conceptual reasoner and the assertions given to the graphical interface.

This article describes a study of personal journal subscriptions of university faculty teaching in arts and professional programs at an undergraduate liberal arts university. Based on personal interviews, this study examines subscriptions with regard to reason for subscription, classification of journal, and importance to the discipline and the faculty member. Overlap with the holdings of the university library, financing of personal subscriptions, and style of reading are also investigated. Results from the two groups are presented separately and compared with the results that were described in part I for the faculty of science. © 1994 John Wiley & Sons, Inc.

Virtually all semantic or object-oriented data models assume that objects have an identity separate from any of their parts, and allow users to define complex object types in which part values may be any other objects. This often results in a choice of query language in which a user can express navigating from one object to another by following a property value path. We consider a constraint language in which one may express equations and functional dependencies over complex object types. The language is novel in the sense that component attributes of individual constraints may correspond to property paths. The kind of equations we consider are also important, because they are a natural abstraction of the class of conjunctive queries for query languages that support property value navigation. In our introductory comments, we give an example of such a query and outline two applications of the constraint theory to problems relating to a choice of access plan for the query. We present a sound and complete axiomatization of the constraint language for the case in which interpretations are permitted to be infinite, where interpretations themselves correspond to a form of directed labeled graph. Although the implication problem for our form of equational constraint alone over arbitrary schema is undecidable, we present decision procedures for the implication problem for both kinds of constraints when the problem schema satisfies a stratification condition, and when all input functional dependencies are keys.>

This article describes a study of personal journal subscriptions of university faculty in science in an undergraduate liberal arts university. Based on personal interviews, this article examines personal subscriptions with regard to reason for subscription, classification of journal, use of an SDI service, and importance to the discipline and the faculty member. Overlap with the holdings of the university library, financing of personal subscriptions, and style of reading were also investigated. Results are mostly as expected, but noteworthy is the influence of subscribing to an SDI service on various aspects of subscriptions. © 1992 John Wiley & Sons, Inc.