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Migrating data to a new database model presents problems if there are existing application programs that must continue to access the data, bu that cannot be converted immediately. If the target database is object-oriented, such a legacy program can be encapsulated as an object or a message. We argue that some applications will benefit from further “reification” of execution instances as database objects...
As a foundation for providing semantics for aggregation within recursion, the structure of subsets of partially ordered domains is studied. We argue that the underlying cause of many of the difficulties encountered in extending deductive database semantics to include aggregation is that set construction does not preserve the structure of the underlying domain very well. We study a binary relation...
Declarative languages for deductive and object-oriented databases require some high-level mechanism for specifying semantic control knowledge. This paper proposes user-supplied subsumption information as a paradigm to specify desired, prefered or useful deductions at the meta level. For this purpose we augment logic programming by subsumption relations and succeed to extend the classical theorems...
This paper addresses the issue of non deterministic extensions of logic database languages. After providing a quick overview of the main proposals in the literature, we concentrate on the analysis of the dynamic choice construct from the point of view of the expressive power. We show how such construct is capable of expressing several interesting deterministic and non deterministic problems, such...
This paper presents the application of combined deductive and object-oriented technologies to a complex scheduling (timetable) problem. This approach emphasizes local propagation of constraints, which we perform with deductive rules, and combines it with global pruning heuristics, which we represent with methods (in a procedural manner) attached to objects. Because both components are essential to...
Developing a declarative approach to schema integration in the context of heterogeneous database systems is a major goal of this research. We take a first step toward this goal in this paper, by developing a simple logic called SchemaLog which is syntactically higher-order but has a first-order semantics. SchemaLog can provide for a logical integration of multiple relational databases in a federation of database systems. We develop a fixpoint theory as well as a sound and complete proof theory for the definite clause fragment of SchemaLog and show their equivalence to the model-theoretic semantics. We argue that a uniform framework for schema integration as well as schema evolution is both desirable and possible. We illustrate the simplicity and power of SchemaLog with a variety of applications involving database programming (with schema browsing), schema integration, schema evolution, and cooperative query answering...
Programs in deductive database and programming systems have a natural meaning that is based upon their mathematical reading as logical rules. High-level ‘explanations’ of a program evaluation/execution can be constructed to provide added functionality: (1) To debug a program by following a chain of deductions leading to an unexpected (and possibly incorrect) conclusion; (2) To follow the derivation...
We present a wide-spectrum algebra and refinement calculus designed to allow one to reason about query optimization in graph-based data models. A query language is wide-spectrum if it can be used to express both user level queries as well as low-level evaluation strategies or access plans. This property enables rule-based query optimization to be viewed as the process of refining expressions...
Numerous structures for database query optimizers have been proposed. Many of those proposals aimed at automating the construction of query optimizers from some kind of specification of optimizer behavior. These specification frameworks do a good job of partitioning and modularizing the kinds of information needed to generate a query optimizer. Most of them represent at least part of this information...
This paper addresses the problem of semantic query reformulation in the context of object-oriented deductive databases. It extends the declarative object-oriented specifications of F-logic proposed by Kifer and Lausen using the semantic query optimization technique developed by Chakravarthy, Grant, and Minker. In general, query processing in object-oriented databases is expensive when a query incorporates...
Deductive databases generalize relational databases by providing support for mecursive views and non-atomic data. Aditi is a deductive database system based on the client-server model: it is inherently multi-user and capable of exploiting parallelism on shared-memory multiprocessors. The back-end uses relational technology for efficiency in the management of disk based data and uses optimization algorithms...
The problem of allowing non-monotonic constructs, such as negation and aggregates, in recursive programs represents a difficult challenge faced by current research in deductive databases. In this paper, we present a solution that combines generality with efficiency, as demonstrated by its implementation in the new LDL++ system. A novel and general treatment of set aggregates, allowing for user-defined...
The IsaLog ¬ model and language are presented. The model has complex objects with classes, relations, and isa hierarchies. The language is strongly typed and declarative. The main issue is the definition of the semantics of the IsaLog language. The novel features are mostly due to the interaction of hierarchies with negation in the body of rules. Two semantics are presented and shown to be equivalent:...
In this paper, we address the complexity issue of reasoning with implication constraints. We consider the problem of deciding whether a conjunctive yes/no-query always produces the empty relation (“no” answer) on database instances satisfying a given set of implication constraints, which we refer to as the IC-refuting problem. We show that several other important problems, such as the query containment...
We propose a query-evaluation algorithm for database specifications consisting of overridable rules (defaults) and non-overridable rules (axioms). Both kinds of rules may contain disjunctions. Preferences among the defaults are given by a partial order which corresponds to a subclass relationship allowing multiple inheritance. We use a bottom-up theorem proving procedure. It is applied to the set...
Path expressions, a central ingredient of query languages for object-oriented databases, are currently used as a purely navigational vehicle. We argue that this does not fully exploit their potential expressive power as a tool to specify connections between objects. In particular, a user should not be required to specify a path to be followed in full, but rather should provide enough information so...
Deductive object-oriented databases advocate the advantage of combining object-oriented and deductive paradigms into a single data model. Certainly, the query language in such a data model has to reflect the amalgamation because it works as the interface to the user and/or application program. This paper proposes a language to formulate queries as classes related to the schema classes and constrained...
We address the issue of updating derived data in universal relation interfaces and in deductive databases. The proposed approach consists in marking those facts whose deletions are desired, and in processing these marks so as to appropriately answer queries. The database semantics is given in a general framework by fixpoint construction of three derivation operators computing exceptions, positive...
We describe data structures that allow efficient updates of materialized classes derived from relationship of classes in object bases. Materialization of derived classes reduces costs of retrievals and increases costs of updates. Costs of updates increase remarkably when several paths of objects derive the same object. If object bases satisfy the superkey condition proposed in this paper, consistencies...
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