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.

Visual query systems (VQSs) are query systems for databases that use visual representations to depict the domain of interest and express related requests. VQSs can be seen as an evolution of query languages adopted into database management systems; they are designed to improve the effectiveness of the human-computer communication. Thus, their most important features are those that determine the nature of the human-computer dialogue. In order to survey and compare existing VQSs used for querying traditional databases, we first introduce a classification based on such features, namely the adopted visual representations and the interaction strategies. We then identify several user types and match the VQS classes against them, in order to understand which kind of system may be suitable for each kind of user. We also report usability experiments which support our claims. Finally, some of the most important open problems in the VQS area are described. 1.

We define formal notions of temporal domain and temporal database, and use them to survey a wide spectrum of temporal query languages. We distinguish between an abstract temporal database and its concrete representations, and accordingly between abstract and concrete temporal query languages. We also address the issue of incomplete temporal information. 1 Introduction A temporal database is a repository of temporal information. A temporal query language is any query language for temporal databases. In this paper we propose a formal notion of temporal database and use this notion in surveying a wide spectrum of temporal query languages. The need to store temporal information arises in many computer applications. Consider, for example, records of various kinds: financial [37], personnel, medical [98], or judicial. Also, monitoring data, e.g., in telecommunications network management [4] or process control, has often a temporal dimension. There has been a lot of research in temporal dat...

Programmers working on large software systems spend a great deal of time examining code and trying to understand it. Code Analysis tools (e.g., cross referencing tools such as CIA and Cscope) can be very helpful in this process. In this paper we describe genoa, an application generator that can produce a whole range of useful code analysis tools. genoa is designed to be language- and front-end independent; it can be interfaced to any front-end for any language that produces an attributed parse tree, simply by writing an interface specification. While genoa programs can perform arbitrary analyses on the parse tree, the genoa language has special, compact iteration operators that are tuned for expressing simple, polynomial time analysis programs; in fact, there is a useful sublanguage of genoa that can express precisely all (and only) polynomial time (PTIME) analysis programs on parse-trees. Thus, we argue that genoa is a convenient "little language" to implement simple, fast analysis t...

We study two important extensions of first-order logic (FO) with iteration, the fixpoint and while queries. The main result of the paper concerns the open problem of the relationship between fixpoint and while: they are the same iff ptime = pspace. These and other expressibility results are obtained using a powerful normal form for while which shows that each while computation over an unordered domain can be reduced to a while computation over an ordered domain via a fixpoint query. The fixpoint query computes an equivalence relation on tuples which is a congruence with respect to the rest of the computation. The same technique is used to show that equivalence of tuples and structures with respect to FO formulas with bounded number of variables is definable in fixpoint. Generalizing fixpoint and while, we consider more powerful languages which model arbitrary computation interacting with a database using a finite set of FO queries. Such computation is modeled by a relational machine...

We present an optimization for integrity constraint verification in distributed databases. The optimization allows a global constraint, i.e. a constraint spanning multiple databases, to be verified by accessing data at a single database, eliminating the cost of accessing remote data. The optimization is based on an algorithm that takes as input a global constraint and data to be inserted into a local database. The algorithm produces a local condition such that if the local data satisfies this condition then, based on the previous satisfaction of the global constraint, the global constraint is still satisfied. If the local data does not satisfy the condition, then a conventional global verification procedure is required. 1 Introduction A clear trend in information systems technology is the distribution of related data across multiple sites. Such systems may vary from tightly-coupled parallel databases to federated information systems. In all cases, one benefit of data distribution is t...

We investigate the in nitary logic L 1! , in which sentences may have arbitrary disjunctions and conjunctions, but they involve only a nite number of distinct variables. We show that various xpoint logics can be viewed as fragments of L 1! , and we describe a game-theoretic characterization of the expressive power of the logic. Finally, we study asymptotic probabilities of properties 1! on nite structures. We show that the 0-1 law holds for L 1! , i.e., the asymptotic probability of every sentence in this logic exists and is equal to either 0 or 1. This result subsumes earlier work on asymptotic probabilities for various xpoint logics and reveals the boundary of 0-1 laws for in nitary logics.

| Research in non-monotonic reasoning has focused largely on the idea of representing knowledge about the world via rules that are generally true but can be defeated. Even if relational databases are nowadays the main tool for storing very large sets of data, the approach of using non-monotonic AI formalisms as relational database query languages has been investigated to a much smaller extent. In this work we propose a novel application of Reiter's default logic by introducing a default query language (DQL) for nite relational databases, which is based on default rules. The main result of this paper is that DQL is as expressive as SO 98 , the existential-universal fragment of secondorder logic. This result is not only of theoretical importance: We exhibit queries {which are useful in practice{ that can be expressed with DQL and can not with other query languages based on non-monotonic logics such as DATALOG with negation under the stable model semantics. In particular, we show that DQ...

This paper describes a new object-oriented model and query algebra that will be used as an input language for the query optimizers that are being built as a part of the EREQ project. The model adopts a uniform view of objects and values and separates syntactic, semantic, and implementation concerns. The algebra addresses issues of type-defined equality and duplicate elimination as well as extensions to bulk types other than sets. 1 Introduction Recently, a great deal of work has been done on the topic of object-oriented query algebras [27, 22, 11] and the modeling of bulk types [4, 25, 19]. These proposals as well as those of other researchers on the topic have explored some of the fundamental issues and provided the starting point for the work reported here. AQUA (A QUery Algebra) is the result of a joint effort among researchers who have participated in the design of previous algebras [26, 30, 31]. AQUA has been designed to address a number of detailed modeling issues that we beli...

this paper, we describe the approach to visual display and manipulation of databases that we have been investigating at the University of Toronto for the past few years. We present an overview and retrospective of the G