MOD

New data models and languages have been the focus of attention in database research in the last decade. The object-oriented paradigm is a convenient vehicle for describing this research, its accomplishments, and for considering which directions are now ...

We address the question of when the structure of a Datalog program with negation guarantees the existence of a fixpoint. We propose a semantics of Datalog programs with negation, which we call the tie–breaking semantics. The tie–breaking semantics can ...

The optimization of a large class of queries is explored, using a powerful normal form recently proven. The queries include the fixpoint and while queries, and an extension of while with arithmetic. The optimization method is evaluated using a ...

A query processor QP uses the rules in a rule base to reduce a given query to a series of attempted retrievals from a database of facts. The Qp's expected cost is the average time it requires to find an answer, averaged over its anticipated set of ...

The common model for analyzing seek distances on a magnetic disk uses a continuous approximation in which the range of motion of the disk arm is the interval [0,1]. In this model, both the current location of the disk arm and the location of the next ...

We study the problem of determining whether a given recursive Datalog program is equivalent to a given nonrecursive Datalog program. We prove triply exponential upper and lower time bounds.

Two types of redundancies in datalog program are considered. Redundancy based on reachability eliminates rules and predicates that do not participate in any derivation tree of a fact for the query predicate. Redundancy based on irrelevance is similar, ...

A chain query seeks, for each input database (viewed as directed graph), all pairs of start and end nodes of paths whose labels spell words in an associated (possibly non context-free) language over some binary predicates. We study the expressive power ...

We present the valid model semantics, a new approach to providing semantics for logic programs with negation, set-terms and grouping. The valid model semantics is a three-valued semantics, and is defined in terms of a ‘normal form’ computation. The ...

The greedy paradigm of algorithm design is a well known tool used for efficiently solving many classical computational problems within the framework of procedural languages. However, it is very difficult to express these algorithms within the ...

We propose a semantics for aggregates in deductive databases based on a notion of minimality. Unlike some previous approaches, we form a minimal model of a program component including aggregate operators, rather than insisting that the aggregate apply ...

Common aggregation predicates have natural definitions in logic, either as first order sentences (min, max, etc.), or with elementary induction over a data structure that represents the relation (sum, count, etc.). The well-founded semantics for logic ...

When failures occur during the execution of distributed commit protocols, the protocols may block in some partitions to avoid inconsistent termination of the transaction, thus making data items in these partitions unavailable for accesses. We present a ...

We present two distributed algorithms for dynamic replication of a data-item in communication networks. The algorithms are adaptive in the sense that they change the replication scheme of the item (i.e. the set of processors at which the data-item is ...

We investigate under which conditions a non-deterministic query is semi-deterministic, meaning that two different results of the query to a database are isomorphic. We also consider uniform semi-determinism, meaning that all intermediate results of the ...

With the availability of high-level declarative query languages in an object-oriented database system (OODB), the burden of choosing an efficient execution plan for a query is transferred from the user to the database system. A natural first step is to ...

Nonblocking algorithms for concurrent data structures guarantee that a data structure is always accessible. This is in contrast to blocking algorithms in which a slow or halted process can render part or all of the data structure inaccessible to other ...

Recently, the scope of databases has been extended to many non-standard applications, and serializability is found to be too restrictive for such applications. In general, two approaches are adopted to address this problem. The first approach considers ...

We propose a language that expresses uniformly queries and updates on knowledgebases consisting of finite sets of relational structures. The language contains an operator that “inserts” arbitrary first-order sentences into knowledgebase. The semantics ...

We study the complexity of several recently proposed methods for updating or revising propositional knowledge bases. In particular, we derive complexity results for the following problem: given a knowledge base T, an update p, and a formula q, decide ...

We propose that Past Metric Temporal Logic (Temporal Logic with real-time operators referring to the past) be used as a language for specifying real-time integrity constraints. Building on our earlier work, we develop efficient, history-less methods of ...

A family of sequence operations (rs-operations), based on pattern matching and including most of the “natural” operations on sequences, is introduced. In order to apply rs-operations to calculus-like query languages, a logic about sequences (SL) is ...

This paper develops a method for reusing and modifying deductive databases. Such methods are needed when new rulebased applications differ only slightly from existing ones or when an application is to be incrementally updated. In order to facilitate ...

We consider a version of the relational model in which relation names may appear as arguments of other relations. Allowing relation names as arguments provides enhanced modelling capabilities, allowing some object-oriented features to be expressed ...