Abstract-Datalog is a database query language based on the logic programming paradigm; it has been designed and intensively studied over the last five years. We present the syntax and semantics of Datalog and its use for querying a relational database. Then, we classify optimization methods for achieving efficient evaluations of Datalog queries, and present the most relevant methods. Finally, we discuss various exhancements of Datalog, currently under study, and indicate what is still needed in order to extend Datalog’s applicability to the solution of real-life problems. The aim of this paper is to provide a survey of research performed on Datalog, also addressed to those members of the database community who are not too familiar with logic programming concepts. Zndex Terms-Deductive databases, logic programming, recursive queries, relational databases, query optimization. I.

We consider the following problem: given a labelled directed graph G and a regular expression R, find all pairs of nodes connected by a simple path such that the concatenation of the labels along the path satisfies R. The problem is motivated by the observation that many recursive queries in relational databases can be expressed in this form, and by the implementation of a query language, G+ , based on this observation. We show that the problem is in general intractable, but present an algorithm than runs in polynomial time in the size of the graph when the regular expression and the graph are free of conflicts. We also present a class of languages whose expressions can always be evaluated in time polynomial in the size of both the graph and the expression, and characterize syntactically the expressions for such languages. Key words. Labelled directed graphs, NP-completeness, polynomial-time algorithms, regular expressions, simple paths AMS(MOS) subject classifications. 68P, 6...

The Internet's core routing infrastructure, while arguably robust and e#cient, has proven to be di#cult to evolve to accommodate the needs of new applications. Prior research on this problem has included new hard-coded routing protocols on the one hand, and fully extensible Active Networks on the other. In this paper, we explore a new point in this design space that aims to strike a better balance between the extensibility and robustness of a routing infrastructure. The basic idea of our solution, which we call declarative routing, is to express routing protocols using a database query language. We show that our query language is a natural fit for routing, and can express a variety of well-known routing protocols in a compact and clean fashion. We discuss the security of our proposal in terms of its computational expressive power and language design. Via simulation, and deployment on PlanetLab, we demonstrate that our system imposes no fundamental limits relative to traditional protocols, is amenable to query optimizations, and can sustain long-lived routes under network churn and congestion.

ODE is a database system and environment based on the object paradigm. It offers one integrated data model for both database and general purpose manipulation. The database is defined, queried and manipulated in the database programming language O++ which is based on C++. O++ borrows and extends the object definition facility of C++, called the class. Classes support data encapsulation and multiple inheritance. We provide facilities for creating persistent and versioned objects, defining sets, and iterating over sets and clusters of persistent objects. We also provide facilities to associate constraints and triggers with objects. This paper presents the linguistic facilities provided in O++ and the data model it supports. 1. INTRODUCTION The object paradigm is a natural way of organizing data as it allows users to structure, retrieve and update data in terms of the application domain. ODE is a database system and environment based on the object paradigm. The database is defined, queri...

We propose a data model and query language that integrates an explicit modeling and querying of graphs smoothly into a standard database environment. For standard applications, some key features of object-oriented modeling are offered such as object classes organized into a hierarchy, object identity, and attributes referencing objects. Querying can be done in a familiar style with a derive statement that can be used like a select... from... where. On the other hand, the model allows for an explicit representation of graphs by partitioning object classes into simple classes, link classes, and path classes whose objects can be viewed as nodes, edges, and explicitly stored paths of a graph (which is the whole database instance). For querying graphs, the derive statement has an extended meaning in that it allows one to refer to subgraphs of the database graph. A powerful rewrite operation is offered for the manipulation of heterogeneous sequences of objects which often occur as a result of accessing the database graph. Additionally there are special graph operations like determining a shortest path or a subgraph and the model is extensible by such operations. Besides being attractive for standard applications, the model permits a natural representation and sophisticated querying of networks, in particular of spatially embedded networks like highways, public transport, etc.

We present constructs for computing aggregate functions over sets of tuples and along paths in a database graph. We show how Datalog can be extended to compute a large class of queries with aggregates without incurring the large expense of a language with general set manipulation capabilities. In particular, we aim for queries that can be executed efficiently in parallel, using the class nc and its various subclasses as formal models of low parallel complexity. Our approach retains the standard relational notion of relations as sets of tuples, not requiring the introduction of multisets. In the case where no rules are recursive, the language is exactly as expressive as Klug's first order language with aggregates. We show that this class of non-recursive programs cannot express transitive closure (unless logspace=nlogspace), thus providing evidence for a widely believed but never proven folk result. We also study the expressive This work has been supported by the Informat...

We define the magic-sets transformation for traditional relational systems (with duplicates, aggregation and grouping), as well as for relational systems extended with recursion. We compare the magic-sets rewriting to traditional optimization techniques for nonrecursive queries, and use performance experiments to argue that the magic-sets transformation is often a better optimization technique. 1 Introduction "Magic-sets" is the name of a query transformation algorithm ([BMSU86]) (and now a class of algorithms Part of this work was done at the IBM Almaden Research Center. Work at Stanford was supported by an NSF grant IRI87 -22886, an Air Force grant AFOSR-88-0266, and a grant of IBM Corporation. y Author's current affiliation: Tandem Computers. z Part of this work was done while the author was visiting IBM Almaden Research Center. Work at Wisconsin was supported by an IBM Faculty Development Award and an NSF grant IRI-8804319. --- Generalized Magic-sets of [BR87], Magic Tem...

This paper presents the notion of Semantic Associations as complex relationships between resource entities. These relationships capture both a connectivity of entities as well as similarity of entities based on a specific notion of similarity called ρ-isomorphism. It formalizes these notions for the RDF data model, by introducing a notion of a Property Sequence as a type. In the context of a graph model such as that for RDF, Semantic Associations amount to specific certain graph signatures. Specifically, they refer to sequences (i.e. directed paths) here called Property Sequences, between entities, networks of Property Sequences (i.e. undirected paths), or subgraphs of ρ-isomorphic Property Sequences. The ability to query about the existence of such relationships is fundamental to tasks in analytical domains such as national security and business intelligence, where tasks often focus on finding complex yet meaningful and obscured relationships between entities. However, support for such queries is lacking in contemporary query systems, including those for RDF. This paper discusses how querying for Semantic Associations might be enabled on the Semantic Web, through the use of an operator ρ. It also discusses two approaches for processing ρqueries on available persistent RDF stores and memory resident RDF data graphs, thereby building on current RDF query languages.

Introduction Many large companies use multiple databases to serve the needs of various application systems. One of the significant problems in managing these databases is maintaining the consistency of inter-related data in an environment consisting of multiple semi-autonomous and heterogeneous systems. We use the term interdependent data to imply that two or more data items stored in different databases are related through an integrity constraint that specifies the data dependency and the consistency requirements between these data items. Management of such data implies that a certain degree of mutual consistency among the interdependent data is maintained. Therefore, the manipulation (including concurrent updates) of the interdependent data must be controlled. In the majority of existing applications, the mutual consistency requirements among multiple databases are either ignored, or the consistency of data is maintained by the application programs that perf

We present new algorithms for computing the transitive closure of large database relations. Unlike iterative algorithms, such as the semi-naive and the logarithmic algorithms, the termination of our algorithms does not depend on the length of paths in the underlying graph (hence, the name direct algorithms). We also present simulation results that show that these direct algorithms perform uniformly better than the best of the iterative algorithms. A side benefit of this work is that we have proposed a new methodology for evaluating the performance of recursive queries. 1. INTRODU~ION With the increasing “non-traditional ” uses of relational databases, several extensions have been proposed to the relational query languages in order to efficiently support these applications. A common operator that appears in many of these proposals is the transitive closure operation (see, for example, Zloofs QBE Il71, Guttman’s l extension to Quel 171, Probe’s traversal recursion [lll, and Agrawal’s (r-extended relational algebra I1 I). In [91, it has been shown that every linearly recursive query can be expressed as a transitive closure possibly preceded and followed by operations already available in relational algebra, once again emphasizing the importance of Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the VWB copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Very Large Data