We investigate the relationship between programming with constraints and database query languages. We show that efficient, declarative database programming can be combined with efficient constraint solving. The key intuition is that the generalization of a ground fact, or tuple, is a conjunction of constraints over a small number of variables. We describe the basic Constraint Query Language design principles and illustrate them with four classes of constraints: real polynomial inequalities, dense linear order inequalities, equalities over an infinite domain, and boolean equalities. For the analysis, we use quantifier elimination techniques from logic and the concept of data complexity from database theory. This framework is applicable to managing spatial data and can be combined with existing multidimensional searching algorithms and data structures.

. Constraints allow programmers and users to state declaratively a relation that should be maintained, rather than requiring them to write procedures to maintain the relation themselves. They are thus useful in such applications as programming languages, user interface toolkits, and simulation packages. In many situations, it is desirable to be able to state both required and preferential constraints. The required constraints must hold. Since the other constraints are merely preferences, the system should try to satisfy them if possible, but no error condition arises if it cannot. A constraint hierarchy consists of a set of constraints, each labeled as either required or preferred at some strength. An arbitrary number of different strengths is allowed. In the discussion of a theory of constraint hierarchies, we present alternate ways of selecting among competing possible solutions, and prove a number of propositions about the relations among these alternatives. We then outline algorit...

A constraint describes a relation to be maintained

. The declarative programming paradigms used in constraint languages can lead to powerful extensions of Codd's relational data model. The development of constraint database query languages from logical database query languages has many similarities with the development of constraint logic programming from logic programming, but with the additional requirements of data efficient, set-at-a-time, and bottomup evaluation. In this overview of constraint query languages (CQLs) we first present the framework of [41]. The principal idea is that: "the k-tuple (or record) data type can be generalized by a conjunction of quantifier-free constraints over k variables". The generalization must preserve various language properties of the relational data model, e.g., the calculus/algebra equivalence, and have time complexity polynomial in the size of the data. We next present an algebra for dense order constraints that is simpler to evaluate than the calculus described in [41], and we sharpen some of...

One-way dataflow constraints have gained popularity in many types of interactive systems because of their simplicity, efficiency, and manageability. Although it is widely acknowledged that multi-way dataflow constraints could make it easier to specify certain relationships in these applications, concerns about their predictability and efficiency have impeded their acceptance. Constraint hierarchies have been developed to address the predictability problem and incremental algorithms have been developed to address the efficiency problem. However, existing incremental algorithms for satisfying constraint hierarchies encounter two difficulties: (1) they are incapable of guaranteeing an acyclic solution if a constraint hierarchy has one or more cyclic solutions, and (2) they require worst-case exponential time to satisfy systems of multi-output constraints. This paper surmounts these difficulties by presenting an 2 incremental algorithm called QuickPlan that satisfies in worst case O(N ) ...

Constraint Logic Programming (CLP) is a new class of programming languages combining the declarativity of logic programming with the efficiency of constraint solving. New application areas, amongst them many different classes of combinatorial search problems such as scheduling, planning or resource allocation can now be solved, which were intractable for logic programming so far. The most important advantage that these languages offer is the short development time while exhibiting an efficiency comparable to imperative languages. This tutorial aims at presenting the principles and concepts underlying these languages and explaining them by examples. The objective of this paper is not to give a technical survey of the current state of art in research on CLP, but rather to give a tutorial introduction and to convey the basic philosophy that is behind the different ideas in CLP. It will discuss the currently most successful computation domains and provide an overview on the different consi...

The ability to identify and represent the knowledge that a human expert has about o particular domoin is a key method in the creation of an expert com-puter system. The first part of this paper demonstrates a methodology for collecting and onalyzing observations of experts at work, in order to find the conceptual framework used for the particular domain. The second part de-velops a representation for qualitative knowledge of the structure ond be-havior of a mechanism. The qualitative simulation, or envisionment, process is given a qualitative structural description of a mechanism and some initiali-zation information. and produces a detailed description of the mechanism’s behavior. The simulation process hos been fully implemented, and its results are shown for a particular diseose mechanisms in nephrology. This vertical slice of the construction of a cognitive model demonstrates an effective knowl-edge acquisition method for the purpose of determining the structure of the representation itself, not simply the content of the knowledge lo be encoded in that representation. Most importantly, it demonstrates the interaction among constraints derived from the textbook knowledge of the domain, from observations of the human expert, ond from the computational requirements of successful performance. 1.

Two major paradigms in computer programming languages are imperative and declarative programming. We describe a scheme for languages that integrate specific features from these two paradigms into a new framework: Constraint Imperative Programming. Along with the framework, we discuss the design and implementation of a particular instance of this framework, Kaleidoscope'90. From the imperative paradigm, constraint imperative programming adopts explicit control flow, state, and assignment. From the declarative paradigm, it adopts explicit, systemmaintained constraints (relations that should hold). There is a strong practical motivation for making this integration: in a typical application, some portions are most clearly described using imperative constructs, while other portions are most clearly described using constraints. By using a constraint imperative language, the most suitable paradigm can be used as appropriate. 1 Introduction We propose to combine two simple techniques--- decl...

We see a trend toward extending object-oriented languages in the direction of databases, and, at the same time, toward extending database systems with object-oriented ideas. On the surface, these two activities seem to be moving in a consistent direction. However, at a deeper level, we see dif-ficulties that may inhibit their ending up at the same point. We feel that many of these difficufties are a result of the underlying assumptions that are inherent in the fields of programming language and database systems research. Many of these assumptions are historical and contribute to a set of cultural biases that often prevent the two communities from interacting as effectively as pos-sible. The purpose of this paper is to try to uncover some of the cultural presuppositions that have inhibited development of a fully integrated database programming language. We have identified database and language features that seem to be difficult to reconcile. We try to uncover the basic problems in these two areas that these features were intended to solve. In order to resolve these problems, we attempt to distinguish fundamental differences from historical artifacts. 1. lntroductlon The database and the programming language communities seem to be moving toward each other in terms of the problems that they are addressing. Database systems have been attempting to increase their power by associating more and more

. Constraint databases generalize relational databases by finitely representable infinite relations. This paper surveys the state of the art in constraint databases: known results, remaining open problems and current research directions. The paper also describes a new algebra for databases with integer order constraints and a complexity analysis of evaluating queries in this algebra. In memory of Paris C. Kanellakis 1 Introduction There is a growing interest in recent years among database researchers in constraint databases, which are a generalization of relational databases by finitely representable infinite relations. Constraint databases are parametrized by the type of constraint domains and constraint used. The good news is that for many parameters constraint databases leave intact most of the fundamental assumptions of the relational database framework proposed by Codd. In particular, 1. Constraint databases can be queried by constraint query languages that (a) have a semantics ba...