Many important problems can be compactly represented as quantified boolean formulas (QBF) and solved by general QBF solvers. To date QBF solvers have mainly focused on determining whether or not the input QBF is true or false. However, additional important information about an application can be gathered from its QBF formulation. In this paper we demonstrate that a circuitbased QBF solver can be exploited to obtain a QResolution proof of the truth or the falsity of a QBF. QBFs have a natural interpretation as a two person game and our main result is to show how, via a simple computation, the moves for the winning player can be computed directly from these proofs. This result shows that the proof is a representation of the winning strategy. In previous approaches the winning strategy has often been represented in a way that makes it hard to verify. In our approach the correctness of the strategy follows directly from the correctness of the proof, which is relatively easy to verify.

Feature Flow Fields are a well-accepted approach for extracting and tracking features. In particular, they are often used to track critical points in time-dependent vector fields and to extract and track vortex core lines. The general idea is to extract the feature or its temporal evolution using a stream line integration in a derived vector field-the so-called Feature Flow Field (FFF). Hence, the desired feature line is a stream line of the FFF. As we will carefully analyze in this paper, the stream lines around this feature line may diverge from it. This creates an unstable situation: if the integration moves slightly off the feature line due to numerical errors, then it will be captured by the diverging neighborhood and carried away from the real feature line. The goal of this paper is to define a new FFF with the guarantee that the neighborhood of a feature line has always converging behavior. This way, we have an automatic correction of numerical errors: if the integration moves slightly off the feature line, it automatically moves back to it during the ongoing integration. This yields results which are an order of magnitude more accurate than the results from previous schemes. We present new stable FFF formulations for the main applications of tracking critical points and solving the Parallel Vectors operator. We apply our method to a number of data sets.

A new method for finding the locus of parallel vectors is presented, called PVsolve. A parallel-vector operator has been proposed as a visualization primitive, as several features can be expressed as the locus of points where two vector fields are parallel. Several applications of the idea have been reported, so accurate and efficient location of such points is an important problem. Previously published methods derive a tangent direction under the assumption that the two vector fields are parallel at the current point in space, then extend in that direction to a new point. PVsolve includes additional terms to allow for the fact that the two vector fields may not be parallel at the current point, and uses a root-finding approach. Mathematical analysis sheds new light on the feature flow field technique (FFF) as well. The root-finding property allows PVsolve to use larger step sizes for tracing parallel-vector curves, compared to previous methods, and does not rely on sophisticated differential equation techniques for accuracy. Experiments are reported on fluid flow simulations, comparing FFF and PVsolve.

Rendering highly complex models can be time and space prohibitive, and decimation is an important tool in providing simplifications. A decimated model may replace the original entirely or provide level-of-detail approximations. We present and evaluate, quantitatively and qualitatively, methods for rapidly decimating volumetric data defined on a tetrahedral grid. Results are compared using both direct volume rendering and isosurface rendering. A mass-based and a density-based decimation error metric are compared, and the mass-based metric is found to be superior. Grid surface vertices are decimated using a geometric error metric, as well as one of the data-based error metrics. Images produced using direct volume rendering and isosurface extraction on grids that are decimated approximately 80% are nearly indistinguishable from similar images using the non-decimated grids, and even at 95% decimation, the rendered images have few artifacts. Rendering speed-up depends upon the renderer used.

We describe an improved, anatomically based approach to modeling and animating animals.Underlying muscles, bones, and generalized tissue are modeled as triangle meshes or ellipsoids.Muscles are deformable discretized cylinders lying between fixed origins and insertions on specific bones.Default rest muscle shapes can be used, or the rest muscle shape can be designed by the user with a small set of parameters.Muscles automatically change shape as the joints move.Skin is generated by voxelizing the underlying components, filtering, and extracting a polygonal isosurface.Isosurface skin vertices are associated with underlying components and move with them during joint motion.Skin motion is consistent with an elastic membrane model.All components are parameterized and can be reused on similar bodies with non-uniformly scaled parts.This parameterization allows a non-uniformly sampled skin to be extracted, maintaining more details at the head and extremities.

A general volume rendering technique is described that efficiently produces images of excellent quality from data defined over irregular grids having a wide variety of formats. Rendering is done in software, eliminating the need for special graphics hardware, as well as any artifacts associated with graphics hardware. Images of volumes with about 1,000,000 cells can be produced in one to several minutes on a workstation with a 150-MHz processor. A significant advantage of this method for applications such as computational fluid dynamics is that it can process multiple intersecting grids. Such grids present problems for most current volume rendering techniques. Also, the wide range of cell sizes does not present difficulties, as it does for many techniques. A spatial hierarchical organization makes it possible to access data from a restricted region efficiently. The tree has greater depth in regions of greater detail, determined by the number of cells in the region. It also makes it possible to render useful "preview" images very quickly by displaying each region associated with a tree node as one cell. Previews show enough detail to navigate effectively in very large data sets. The algorithmic techniques include use of a k-d tree, with prefix-order partitioning of triangles, to reduce the number of primitives that must be processed for one rendering, coarse-grain parallelism for a shared-memory MIMD architecture, a new perspective transformation that achieves greater numerical accuracy, and a scanline algorithm with depth sorting and a new clipping technique.

No abstract available.

A popular technique for rendition of isosurfaces in sampled data is to consider cells with sample points as corners and approximate the isosurface in each cell by one or more polygons whose vertices are obtained by interpolation of the sample data. That is, each polygon vertex is a point on a cell edge, between two adjacent sample points, where the function is estimated to equal the desired threshold value. The two sample points have values on opposite sides of the threshold, and the interpolated point is called an intersection point . When one cell face has an intersection point in each of its four edges, then the correct connection among intersection points becomes ambiguous. An incorrect connection can lead to erroneous topology in the rendered surface, and possible discontinuities. We show that disambiguation methods, to be at all accurate, need to consider sample values in the neighborhood outside the cell. This paper studies the problems of disambiguation, reports on some solutions, and presents some statistics on the occurrence of such ambiguities. A natural way to incorporate neighborhood information is through the use of calculated gradients at cell corners. They provide insight into the behavior of a function in well-understood ways. We introduce two gradient consistency heuristics that use calculated gradients at the corners of ambiguous faces, as well as the function values at those corners, to disambiguate at a reasonable computational cost. These methods give the correct topology on several examples that caused problems for other methods we examined.

A model is described to estimate the size of intermediate relations produced by large relational algebra expressions, in particular, those containing several equi-joins. The intended application is within query optimization searches, where fast estimates are needed as many alternative plans are examined. It is shown that previous methods, which use an independence assumption when several attributes are joined, can lead to unrealistically low size estimates. This method attempts to overcome that problem by the introduction of “virtual domains”, which avoid the independence assumption. The method does not require extensive statistics about the database. After describing an “exact” version, an approximation that is simpler and faster is presented.

Fast techniques for direct volume rendering over curvilinear grids (common to computational fluid dynamics and finite element analysis) are developed. Three new projection methods that use polygon-rendering hardware for speed are presented and compared with each other and with previous methods for tetrahedral grids and rectilinear grids. A simplified algorithm for visibility ordering, based on a combination of breadth-first and depth-first searches, is described. A new multi-pass blending method is described that reduces visual artifacts that are introduced by linear interpolation in hardware where exponential interpolation is needed. Visualization tools that permit rapid data banding and cycling through transfer functions, as well as region restriction, are described.>

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 programs provides an interpretation of such definitions. The interpretation of first-order aggregates seems to be quite natural and intuitively satisfying, even in the presence of recursion through aggregation. Care is needed to get useful results on inductive aggregates, however. A basic building block is the “subset” predicate, which states that a data structure represents a subset of an IDB predicate, and which is definable in the well-founded semantics. The analogous “superset” is also definable, and their combination yields a “generic” form of findall. Surprisingly, findall must be used negatively to obtain useful approximations when the exact relation is not yet known.

The large size of many volume data sets often prevents visualization algorithms from providing interactive rendering. The use of hierarchical data structures can ameliorate this problem by storing summary information to prevent useless exploration of regions of little or no current interest within the volume. This paper discusses research into the use of the octree hierarchical data structure when the regions of current interest can vary during the application, and are not known a priori . Octrees are well suited to the six-sided cell structure of many volumes. A new space-efficient design is introduced for octree representations of volumes whose resolutions are not conveniently a power of two; octrees following this design are called branch-on-need octrees (BONOs). Also, a caching method is described that essentially passes information between octree neighbors whose visitation times may be quite different, then discards it when its useful life is over. Using the application of octrees to isosurface generation as a focus, space and time comparisons for octree-based versus more traditional “marching” methods are presented.

Article Free Access Share on Termination detection in logic programs using argument sizes (extended abstract) Authors: Kirack Sohn University of California, Santa Gruz University of California, Santa GruzView Profile , Allen Van Gelder University of California, Santa Gruz University of California, Santa GruzView Profile Authors Info & Claims PODS '91: Proceedings of the tenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systemsApril 1991 Pages 216–226https://doi.org/10.1145/113413.113433Published:01 April 1991Publication History 62citation272DownloadsMetricsTotal Citations62Total Downloads272Last 12 Months16Last 6 weeks2 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

Direct volume rendering offers the opportunity to visualize all of a three-dimensional sample volume in one image. However, processing such images can be very expensive and good quality high-resolution images are far from interactive. Projection approaches to direct volume rendering process the volume region by region as opposed to ray-casting methods that process it ray by ray. Projection approaches have generated interest because they use coherence to provide greater speed than ray casting and generate the image in a layered, informative fashion. This paper discusses two topics: First, it introduces a projection approach for directly rendering rectilinear, parallel-projected sample volumes that takes advantage of coherence across cells and the identical shape of their projection. Second, it considers the repercussions of various methods of integration in depth and interpolation across the scan plane. Some of these methods take advantage of Gouraud-shading hardware, with advantages in speed but potential disadvantages in image quality.

A general logic program (abbreviated to "program" hereafter) is a set of rules that have both positive and negative subgoals. It is common to view a deductive database as a general logic program consisting of rules (IDB) sitting above elementary relations (EDB, facts). It is desirable to associate one Herbrand model with a program and think of that model as the "meaning of the program," or its "declarative semantics." Ideally, queries directed to the program would be answered in accordance with this model. Recent research indicates that some programs do not have a "satisfactory" total model; for such programs, the question of an appropriate partial model arises. We introduce unfounded sets and well-founded partial models, and define the well-founded semantics of a program to be its well-founded partial model. If the well-founded partial model is in fact a total model, we call it the well-founded model. We show that the class of programs possessing a total well-founded model properly in...

Not all queries in relational calculus can be answered sensibly when disjunction, negation, and universal quantification are allowed. The class of relation calculus queries or formulas that have sensible answers is called the domain independent class which is known to be undecidable. Subsequent research has focused on identifying large decidable subclasses of domain independent formulas. In this paper we investigate the properties of two such classes: the evaluable formulas and the allowed formulas. Although both classes have been defined before, we give simplified definitions, present short proofs of their main properties, and describe a method to incorporate equality. Although evaluable queries have sensible answers, it is not straightforward to compute them efficiently or correctly. We introduce relational algebra normal form for formulas from which form the correct translation into relational algebra is trivial. We give algorithms to transform an evaluable formula into an equivalent allowed formula and from there into relational algebra normal form. Our algorithms avoid use of the so-called Dom relation, consisting of all constants appearing in the database or the query. Finally, we describe a restriction under which every domain independent formula is evaluable and argue that the class of evaluable formulas is the largest decidable subclass of the domain independent formulas that can be efficiently recognized.

In a logic program the feasible argument sizes of derivable facts involving an n-ary predicate are viewed as a set of points in the positive orthant of Rn. We investigate a method of deriving constraints on the feasible set in the form of a polyhedral convex set in the positive orthant, which we call a polycone. Faces of this polycone represent inequalities proven to hold among the argument sizes. These inequalities are often useful for selecting an evaluation method that is guaranteed to terminate for a given logic procedure. The methods may be applicable to other languages in which the sizes of data structures can be determined syntactically.

We introduce and describe the alternating fixpoint of a logic program with negation. The underlying idea is to monotonically build up a set of negative conclusions until the least fixpoint is reached, using a transformation related to the one that defines stable models, developed by Gelfand and Lifschitz. From a fixed set of negative conclusions, we can derive the positive conclusions that follow (without deriving any further negative ones), by traditional Horn clause semantics. The union of positive and negative conclusions is called the alternating fixpoint partial model. The name “alternating” was chosen because the transformation runs in two passes; the first pass transforms an underestimate of the set of negative conclusions into an (intermediate) overestimate; the second pass transforms the overestimates into a new underestimate; the composition of the two passes is monotonic.

Abstract The balanced packet distribution problem on a ring of n processors requires that randomly arriving packets be stored at nodes as evenly as possible by passing packets (and other messages) around the ring. We give a protocol to achieve balanced distribution with an average message complexity of √n per packet and to show that the protocol is optimal, up to lower order terms, for unidirectional rings.

The problem of dynamic processor allocation in PRAMs (programmable random-access memories) is discussed, and differentiated from that of static allocation. The version of the PRAM considered, also called the CREW model is a parallel computer with global memory accessible in unit time; it allows concurrent reads, but requires exclusive writes. Two dynamic processor allocation problems for P processors are distinguished. One, called assignment from numbers, has an Omega (log P) lower bound, even when the number of tasks is O( square root P). The second, called assignment from leaders, has faster solutions. A constant-time solution for O( square root P) tasks is known; it is generalized to O(P/sup 1-1/k/) tasks in time O(k). Handling O(P) tasks requires a different approach and an algorithm that runs in time O(log log P) is proposed which is asymptotically optimal within a constant factor. The implications of these two versions of dynamic allocation on sublogarithmic merge algorithms are discussed.>

A general logic program (abbreviated to “program” hereafter) is a set of rules that have both positive and negative subgoals. It is common to view a deductive database as a general logic program consisting of rules (IDB) sitting above elementary relations (EDB, facts). It is desirable to associate one Herbrand model with a program and think of that model as the “meaning of the program,” or its “declarative semantics.” Ideally, queries directed to the program would be answered in accordance with this model. We introduce unfounded sets and well-founded partial models, and define the well-founded semantics of a program to be its well-founded partial model. If the well-founded partial model is in fact a model, we call it the well-founded model, and say the program is “well-behaved”. We show that the class of well-behaved programs properly includes previously studied classes of “stratified” and “locally stratified” programs Gelfand and Lifschits have proposed a definition of “unique stable model” for general logic programs. We show that a program has a unique stable model if it has a well-founded model, in which case they are the same. We discuss why the converse is not true.

Considered is the question of whether top-down (Prolog-like) evaluation of a set of logical rules can be guaranteed to terminate. The NAIL! system is designed to process programs consisting of logical rules and to select, for each fragment of the program, the best from among many possible strategies for its evaluation. In the context of such a system, it is essential that termination tests be fast. Thus, the “uniqueness” property of logical rules is introduced. This property is satisfied by many of the common examples of rules and is easily recognized. For rules with this property, a set of inequalities, whose satisfaction is sufficient for termination of the rules, can be generated in polynomial time. Then a polynomial test for satisfaction of constraints generated by this process is given.

Not all queries in relational calculus can be answered “sensibly” once disjunction, negation, and universal quantification are allowed. The class of relational calculus queries, or formulas, that have “sensible” answers is called the domain independent class, which is known to be undecidable. Subsequent research has focused on identifying large decidable subclasses of domain independent formulas In this paper we investigate the properties of two such classes the evaluable formulas and the allowed formulas. Although both classes have been defined before, we give simplified definitions, present short proofs of their man properties, and describe a method to incorporate equality.

We consider the parallel time complexity of logic programs without function symbols, called logical query programs, or Datalog programs. We give a PRAM algorithm for computing the minimum model of a logical query program, and show that for programs with the "polynomial fringe property," this algorithm runs in logarithmic time. As a result, the "linear" and "piecewise linear" classes of logic programs are in NC. Then we examine several nonlinear classes in which the program has a single recursive rule that is an "elementary chain" We show that certain nonlinear programs are related to GSM mappings of a balanced parentheses language, and that this relationship implies the "polynomial fringe property;" hence such programs are in NC. Finally, we describe an approach for demonstrating that certain logical query programs are log space complete for P, and apply it to both elementary single rule programs and nonelementary programs.

article Free Access Share on A message passing framework for logical query evaluation Author: Allen Van Gelder Stanford University Stanford UniversityView Profile Authors Info & Claims ACM SIGMOD RecordVolume 15Issue 2June 1986 pp 155–165https://doi.org/10.1145/16856.16870Published:15 June 1986Publication History 43citation305DownloadsMetricsTotal Citations43Total Downloads305Last 12 Months7Last 6 weeks0 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

System/U is a universal relation database system under development at Standford University which uses the language C on UNIX. The system is intended to test the use of the universal view, in which the entire database is seen as one relation. This paper describes the theory behind System/U, in particular the theory of maximal objects and the connection between a set of attributes. We also describe the implementation of the DDL (Data Description Language) and the DML (Data Manipulation Language), and discuss in detail how the DDL finds maximal objects and how the DML determines the connection between the attributes that appear in a query.

Pseudo-random number generators of the power residue (sometimes called congruential or multiplicative) type are discussed and results of statistical tests performed on specific examples of this type are presented. Tests were patterned after the methods of MacLaren and Marsaglia (M&M). The main result presented is the discovery of several power residue generators which performed well in these tests. This is important because, of all the generators using standard methods (including power residue) that were tested by M&M, none gave satisfactory results. The overall results here provide further evidence for their conclusion that the types of tests usually encountered in the literature do not provide an adequate index of the behavior of n -tuples of consecutively generated numbers. In any Monte Carlo or simulation problem where n supposedly independent random numbers are required at each step, this behavior is likely to be important. Finally, since the tests presented here differ in certain details from those of M&M, some of their generators were retested as a check. A cross-check shows that results are compatible; in particular, if a generator failed one of their tests badly, it also failed the present author's corresponding test badly.