Proceedings of the 2015 ACM SIGMOD International Conference on Management of Data, 2015
We propose to demonstrate Rubato DB, a highly scalable NewSQL system, supporting various consiste... more We propose to demonstrate Rubato DB, a highly scalable NewSQL system, supporting various consistency levels from ACID to BASE for big data applications. Rubato DB employs the staged grid architecture with a novel formula based protocol for distributed concurrency control. Our demonstration will present Rubato DB as one NewSQL database management system running on a collection of commodity servers against two of benchmark sets. The demo attendees can modify the configuration of system size, fine-tune the query workload, and visualize the performance on the fly by the graphical user interface. Attendees can experiment with various system scales, and thus grasp the potential scalability of Rubato DB, whose performance, with the increase of the number of servers used, can achieve a linear growth for both OLTP application with the strong consistency properties and key-value storage applications with the weak consistency properties.
In this paper, we first define the correlated table of an SQL query without nested subqueries whi... more In this paper, we first define the correlated table of an SQL query without nested subqueries which extends the result set of an SQL query to a set of result sets, one for each distinct binding tuple. We then present an algorithm to convert any SQL query with nested subqueries to a correlated query without nested subqueries. The proposed algorithm provides a simple but very effective method unnest nested queries and thus can be used to efficiently evaluate nested queries in distributed database systems. Keyword: query evaluation, distributed databases, nested queries ————————————————
In this paper we propose the minimal well-founded semantics for logic programs with negation base... more In this paper we propose the minimal well-founded semantics for logic programs with negation based on the xpoint of the double Gelfond-Lifschitz transformation which overcomes the existing problems associated with the stable, the well-founded, and the stable class semantics. By representing logic programs as autoepistemic theories, we are able to represent v arious semantics as simple circumscription formulas
Recent proposals for semantics of default theories are all based on some types of weaker notion o... more Recent proposals for semantics of default theories are all based on some types of weaker notion of extensions. T h i s i s t ypi ed in the well-founded semantics and the extension class semantics for default theories. Although these semantics solve the noextension problem in Reiter's default logic, they also present a departure from Reiter's original extension semantics, even for default theories which can be completely characterized by the extension semantics. This results in a weaker capability f o r skeptical reasoning. In this paper we propose a semantics for default theories, based on van Gelder's alternating xpoint theory. The distinct feature of this semantics is its preservation of Reiter's semantics when a default theory is not considered \problematic" under Reiter's semantics. Di erences arise only when a default theory has no extensions, or has only \biased extensions" under Reiter's semantics. This feature allows skeptical reasoning in Reiter's logic to be properly preserved in the new semantics. By the familiar, natural translation from logic programs to default theories, the semantics proposed for default theories provides a natural extension to the stable model semantics of normal logic programs.
The AGM postulates for knowledge base revision are a set of rationality p o stulates that revisio... more The AGM postulates for knowledge base revision are a set of rationality p o stulates that revision operations on knowledge systems should satisfy. De ning an appropriate semantics for belief revision that satis es all of the postulates has been considered a challenging problem. In this paper we present a n o vel application of circumscription to de ning a semantics of belief revision systems. First, a rst-order knowledge base is represented by a set of formulas in a rst order epistemic belief language that contains objective propositions as well as belief propositions. Secondly, w e de ne a revision semantics by applying a form of priority circumscription to the belief representation of the knowledge base. We prove that the semantics de ned in this way satis es the AGM postulates that are reformulated in our belief language.
The pyramidal inversion of trisubstituted heteroatoms is well-recognized. However, the stereochem... more The pyramidal inversion of trisubstituted heteroatoms is well-recognized. However, the stereochemistry of bicoordinated heteroatoms is poorly developed and few examples assumedly isomerize by double-torsion motion or bond-angle inversion. Here, by using ab initio molecular dynamics combined with metadynamics simulation, we reveal an unexpected competing isomerization mechanism, namely dynamic π → σ* negative hyperconjugation induced coupled rotation of bond and bond angle leads to helix inversion in bis(trifluoromethane)sulfonamide (TFSI -), making TFSI -follow four distinct trans-cis isomerization pathways with diverse energy barriers (12-52 kJ mol -1 ) which are significantly higher than 3.6 kJ mol -1 of sole pathway estimated by conventional static calculations. Our quantitative simulations and experiments results confirm the positive correlation between overall stability of cis-TFSI -with polarity of countercations. The melting points (Tm) of TFSI --based ionic liquids (ILs) linearly rise with the conformational rigidity of TFSI -in the ion pair state, offering a new fundamental perspective on the origin of low Tm of ILs.
Global SLS-resolution is a well-known procedural semantics for top-down computation of queries un... more Global SLS-resolution is a well-known procedural semantics for top-down computation of queries under the well-founded model. It inherits from SLDNF-resolution the linearity property of derivations, which makes it easy and efficient to implement using a simple stack-based memory structure. However, like SLDNF-resolution it suffers from the problem of infinite loops and redundant computations. To resolve this problem, in this paper we develop a new procedural semantics, called SLTNF-resolution, by enhancing Global SLS-resolution with loop cutting and tabling mechanisms. SLTNFresolution is sound and complete w.r.t. the well-founded semantics for logic programs with the bounded-term-size property, and is superior to existing linear tabling procedural semantics such as SLT-resolution.
Recursive loops in a logic program present a challenging problem to the PLP framework. On the one... more Recursive loops in a logic program present a challenging problem to the PLP framework. On the one hand, they loop forever so that the PLP backward-chaining inferences would never stop. On the other hand, they generate cyclic influences, which are disallowed in Bayesian networks. Therefore, in existing PLP approaches logic programs with recursive loops are considered to be problematic and thus are excluded. In this paper, we propose an approach that makes use of recursive loops to build a stationary dynamic Bayesian network. Our work stems from an observation that recursive loops in a logic program imply a time sequence and thus can be used to model a stationary dynamic Bayesian network without using explicit time parameters. We introduce a Bayesian knowledge base with logic clauses of the form A ← A 1 , ..., A l , true, Context, T ypes, which naturally represents the knowledge that the A i s have direct influences on A in the context Context under the type constraints T ypes. We then use the wellfounded model of a logic program to define the direct influence relation and apply * A preliminary version appears in the 15th International Conference on Inductive Logic Programming. SLG-resolution to compute the space of random variables together with their parental connections. We introduce a novel notion of influence clauses, based on which a declarative semantics for a Bayesian knowledge base is established and algorithms for building a two-slice dynamic Bayesian network from a logic program are developed.
We introduce a method of verifying termination of logic programs with respect to concrete queries... more We introduce a method of verifying termination of logic programs with respect to concrete queries (instead of abstract query patterns). A necessary and sufficient condition is established and an algorithm for automatic verification is developed. In contrast to existing query pattern-based approaches, our method has the following features: (1) It applies to all general logic programs with non-floundering queries. (2) It is very easy to automate because it does not need to search for a level mapping or a model, nor does it need to compute an interargument relation based on additional mode or type information. (3) It bridges termination analysis with loop checking, the two problems that have been studied separately in the past despite their close technical relation with each other.
ACM Transactions on Computational Logic, Oct 1, 2003
We present a new characterization of termination of general logic programs. Most existing termina... more We present a new characterization of termination of general logic programs. Most existing termination analysis approaches rely on some static information about the structure of the source code of a logic program, such as modes/types, norms/level mappings, models/interargument relations, and the like. We propose a dynamic approach that employs some key dynamic features of an infinite (generalized) SLDNF-derivation, such as repetition of selected subgoals and recursive increase in term size. We also introduce a new formulation of SLDNF-trees, called generalized SLDNF-trees. Generalized SLDNF-trees deal with negative subgoals in the same way as Prolog and exist for any general logic programs.
Infinite loops and redundant computations are long recognized open problems in Prolog. Two ways h... more Infinite loops and redundant computations are long recognized open problems in Prolog. Two ways have been explored to resolve these problems: loop checking and tabling. Loop checking can cut infinite loops, but it cannot be both sound and complete even for function-free logic programs. Tabling seems to be an effective way to resolve infinite loops and redundant computations. However, existing tabulated resolutions, such as OLDT-resolution, SLG-resolution, and Tabulated SLS-resolution, are non-linear because they rely on the solution-lookup mode in formulating tabling. The principal disadvantage of non-linear resolutions is that they cannot be implemented using a simple stack-based memory structure like that in Prolog. Moreover, some strictly sequential operators such as cuts may not be handled as easily as in Prolog. In this paper, we propose a hybrid method to resolve infinite loops and redundant computations. We combine the ideas of loop checking and tabling to establish a linear tabulated resolution called TP-resolution. TP-resolution has two distinctive features: (1) It makes linear tabulated derivations in the same way as Prolog except that infinite loops are broken and redundant computations are reduced. It handles cuts as effectively as Prolog. (2) It is sound and complete for positive logic programs with the bounded-term-size property. The underlying algorithm can be implemented by an extension to any existing Prolog abstract machines such as WAM or ATOAM.
Previously we have proposed a logic, called priority logic 18, 20], where a theory consists of a ... more Previously we have proposed a logic, called priority logic 18, 20], where a theory consists of a collection of logic programming-like inference rules (without default negation) and a priority constraint among them. We showed that nonmonotonic reasoning in general can be viewed as selecting monotonic inferences that satisfy the speci ed priority constraints. The goal of this paper is to investigate how semantics of disjunctive programs can be understood as selecting monotonic inferences. We focus on credulous semantics. We show that the stable semantics of a disjunctive program can be represented by priority logic. The highlight of this paper is an interesting new semantics for disjunctive programs, discoved during this study, which has an abductive interpretation in the sense of Eshghi and Kowalski, whose abductive procedure can be adopted to serve as a credulous proof procedure for the new semantics.
In many database applications designers can easily provide at least some information about the re... more In many database applications designers can easily provide at least some information about the relative importance of the information to be stored and manipulated While of potentially high value the ordering information is typically only partial Here we address the issue of updates in such partially ordered situations which we call epistemically strati ed databases In the current database theory literature Alchourr on G ardenfors and Makinson AGM have proposed a collection of rationality postulates that de ne rational updates to deductively closed databases We reformulate the AGM framework to accomodate empistemically strati ed databases and to relax the closure requirement Our immediate goal is to exploit the use of partial ordering information and to relax the logical omniscient avour of the closure condition A more ambitious goal is only hinted at it is motivated by a desire to develop a more gen eral theory of updates that integrates the naturally related ideas in arti cial inte...
In this paper we propose the minimalwell founded semantics for logic programs with negation based... more In this paper we propose the minimalwell founded semantics for logic programs with negation based on the xpoint of the double Gelfond Lifschitz transformation which overcomes the existing problems associated with the stable the well founded and the stable class semantics By representing logic programs as autoepistemic theories we are able to represent various semantics as simple circumscription formulas
In this paper, we propose a new structure-based approach, called Xregion, to store XML data in re... more In this paper, we propose a new structure-based approach, called Xregion, to store XML data in relational databases. Our approach first partitions an XML document into several disjoint regions according to the cardinality of element nodes, and then maps these regions into separate relations. Our experimental results demonstrate that the proposed approach dramatically improves the performance of queries on the XML data over the existing approaches.
In this paper, we propose a new structure-based approach, called Xregion, to storing XML data in ... more In this paper, we propose a new structure-based approach, called Xregion, to storing XML data in relational databases. Our approach first partitions an XML document into several disjoint regions according to the cardinality of element nodes, and then maps these regions into separate relations. The experimental results demonstrate that the proposed approach dramatically improves the performance of queries on the XML data over the generic mapping approaches.
Recent proposals for semantics of default theories are all based on some types of weaker notion o... more Recent proposals for semantics of default theories are all based on some types of weaker notion of extensions This is typi ed in the well founded semantics and the extension class semantics for default theories Although these semantics solve the no extension problem in Reiter s default logic they also present a departure from Reiter s original extension semantics even for default theories which can be completely char acterized by the extension semantics This results in a weaker capability for skeptical reasoning In this paper we propose a semantics for default theories based on van Gelder s alternating xpoint theory The distinct feature of this semantics is its preservation of Reiter s semantics when a default theory is not considered problematic under Reiter s semantics Di erences arise only when a default theory has no extensions or has only biased extensions under Reiter s semantics This feature allows skeptical reasoning in Reiter s logic to be properly preserved in the new sema...
2014 IEEE International Conference on Big Data (Big Data), 2014
Big data applications demand and consequently lead to developments of large-scale data management... more Big data applications demand and consequently lead to developments of large-scale data management systems, which provide high scalability by partitioning data across multiple servers. Since conventional transactional access is quite expensive, many real world large-scale distributed systems eschew transactional functionality and adopt semantics of atomic multipartition operations. Accordingly, BASE, a consistency model weaker than ACID, is commonly used to guarantee availability. In this work, we identify a new consistency model-BASIC (Basic Availability, Scalability, Instant Consistency) that matches the requirements where extra efforts are not needed to manipulate inconsistent soft states. We present a timestamp-based formula protocol for BASIC that can enforce Instant Consistency while achieving linear scalability (via logical formula caching, dynamic timestamp ordering) and achieve Basic Availability in the presence of partial failure and network partition (via partition independence, genuine atomic commit). Our extensive experimental results verify the scalability of BASIC and demonstrate that the limited overhead induced by BASIC pays a reasonable price for keeping all soft states consistent.
This paper studies the semantics for the class of all defeasible (inheritance) networks, includin... more This paper studies the semantics for the class of all defeasible (inheritance) networks, including cyclic and inconsistent networks using a transformation approach. First we show that defeasible networks can be translated, tractably, to default theories while preserving Horty's offpath credulous semantics for all consistent networks. Using the existing methods in dealing with the semantics of default logic, we are able to provide a tractable skeptical semantics, the well-founded semantics, and a new credulous semantics, the regular semantics, both of which are defined for any defeasible network. Furthermore, we show that these semantics are based on the same principle of specificity used by Horty in defining his credulous semantics of defeasible networks. 1 Introduction Two fundamental problems are to be addressed in this paper. First, the semantics of defeasible networks has previously been studied mainly under the assumption that such a network is acyclic and consis...
Reiter has proposed extended relational theory to formulate relational databases with null values... more Reiter has proposed extended relational theory to formulate relational databases with null values and presented a query evaluation algorithm for such databases. However, due to indefinite information brought in by null values, Reiter's algorithm is sound but not complete. In this paper, we first propose an extended relation to represent indefinite information in relational databases. Then, we define an extended relational algebra for extended relations. Based on Reiter's extended relational theory, and our extended relations and the extended relational algebra, we present a sound and complete query evaluation algorithm for relational databases with null values
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Papers by Li-Yan Yuan