Information mediation in cyberspace: Scalable methods for declarative information networks

An end-to-end discussion, from logical architecture to implementation, of issues and design decisions in declarative information networks is presented. A declarative information network is defined to be a dynamic and decentralized structure where value-added services are declared and applied as mediators in a scalable and controlled manner. A primary result is the need to adopt dynamically linked ontologies as the semantic basis for knowledge sharing in scalable networks. It is shown that data mining techniques provide a promising basis upon which to explore and develop this result. Our prototype system, entitled Mystique, is described in terms of KQML, distributed object management, and distributed agent execution. An example shows how we map our architecture into the World Wide Web (WWW) and transform the appearance of the WWW into an intelligently integrated and multi-subject distributed information network.     

Declarative semantics of transactions in ORM

In order to specify databases completely at the conceptual level, conceptual database specification languages should contain a data definition (sub)language (DDL), for specifying data structures (+constraints), a data retrieval (sub)language (DRL), for specifying queries, as well as a (declarative) data manipulation (sub)language (DML), for specifying transactions.Object Role Modeling (ORM) is a powerful method for designing and querying database models at the conceptual level. By means of verbalization the application is also described in natural language as used by domain experts, for communication and validation purposes. ORM currently comprises a DDL and a DRL (ConQuer). However, the ORM-method does not yet contain an expressive DML for specifying transactions at the conceptual level.In an earlier paper we designed a syntactic extension of the ORM-method with a DML for specifying transactions at the conceptual level in a purely declarative way. For all transactions we proposed syntaxes, verbalizations, and diagrams. However, we did not give a formal semantics then.The purpose of this paper is to add a clear, formal and purely declarative semantics to the proposed ORM-transactions. The paper also formally defines rollbacks and illustrates everything with examples (including a solution to a well-known transaction specification problem). The extension of ORM with an expressive set of completely declaratively specified transactions makes ORM complete as a database specification method at the conceptual level.     

Specifying communication in distributed information systems

We present two logics that allow specifying distributed information systems, emphasizing communication among sites. The low-level logic offers features that are easy to implement but awkward to use for specification, while the high-level logic offers convenient specification features that are not easy to implement. We show that specifications may be automatically translated to in a sound and complete way. In order to prove soundness and completeness, we define our translation as a simple map of institutions. Our result may be useful for making implementation platforms like Corba easier accessible by providing high-level planning and specification methods for communication. Received: 28 September 1998 / 18 November 1999     

Intelligent non-visual navigation of complex HTML structures

This paper provides an overview of a project aimed at using knowledge-based technology to improve accessibility of the Web for visually impaired users. The focus is on the multi-dimensional components of Web pages (tables and frames); our cognitive studies demonstrate that spatial information is essential in comprehending tabular data, and this aspect has been largely overlooked in the existing literature. Our approach addresses these issues by using explicit representations of the navigational semantics of the documents and using a domain-specific language to query the semantic representation and derive navigation strategies. Navigational knowledge is explicitly generated and associated to the tabular and multi-dimensional HTML structures of documents. This semantic representation provides to the blind user an abstract representation of the layout of the document; the user is then allowed to issue commands from the domain-specific language to access and traverse the document according to its abstract layout. Published online: 6 November 2002     

PEGASUS: mining peta-scale graphs

In this paper, we describe PeGaSus, an open source Peta Graph Mining library which performs typical graph mining tasks such as computing the diameter of the graph, computing the radius of each node, finding the connected components, and computing the importance score of nodes. As the size of graphs reaches several Giga-, Tera- or Peta-bytes, the necessity for such a library grows too. To the best of our knowledge, PeGaSus is the first such library, implemented on the top of the Hadoop platform, the open source version of MapReduce. Many graph mining operations (PageRank, spectral clustering, diameter estimation, connected components, etc.) are essentially a repeated matrix-vector multiplication. In this paper, we describe a very important primitive for PeGaSus, called GIM-V (generalized iterated matrix-vector multiplication). GIM-V is highly optimized, achieving (a) good scale-up on the number of available machines, (b) linear running time on the number of edges, and (c) more than 5 times faster performance over the non-optimized version of GIM-V. Our experiments ran on M45, one of the top 50 supercomputers in the world. We report our findings on several real graphs, including one of the largest publicly available Web graphs, thanks to Yahoo!, with ≈ 6.7 billion edges.     

Declarative representations of multiagent systems

This paper explores the specification and semantics of multiagent problem-solving systems, focusing on the representations that agents have of each other. It provides a declarative representation for such systems. Several procedural solutions to a well-known test-bed problem are considered, and the requirements they impose on different agents are identified. A study of these requirements yields a representational scheme based on temporal logic for specifying the acting, perceiving, communicating, and reasoning abilities of computational agents. A formal semantics is provided for this scheme. The resulting representation is highly declarative, and useful for describing systems of agents solving problems reactively     

Generating semantically valid test inputs using constrained input grammars

ContextGenerating test cases based on software input interface is a black-box testing technique that can be made more effective by using structured input models such as input grammars. Automatically generating grammar-based test inputs may lead to structurally valid but semantically invalid inputs that may be rejected in early semantic error checking phases of a system under test.ObjectiveThis paper aims to introduce a method for specifying a grammar-based input model with the model’s semantic constraints to be used in the generation of positive test inputs. It is also important that the method can generate effective test suites based on appropriate grammar-based coverage criteria.MethodFormal specification of both input structure and input semantics provides the opportunity to use model instantiation techniques to create model instances that satisfy all specified constraints. The input interface of a subject system can be specified using a high-level specification scheme such as attribute grammars, and a transformation function from this scheme to an instantiable formal modeling language can generate the desired model instances.ResultsWe propose a declarative grammar-based input specification method that is based on a variation of attribute grammars and allows the user to specify input constraints in addition to input structure. The model can be instantiated automatically to generate structurally and semantically valid test inputs. The proposed method has the capability to specify test requirements and coverage criteria and use them to generate valid test suites that satisfy test coverage criteria requirements.ConclusionThe work presented in this paper provides a black-box test generation method for grammar-based software inputs that can automatically generate criteria-covering test suites.     

A query language for XML

An important application of XML is the interchange of electronic data (EDI) between multiple data sources on the Web. As XML data proliferates on the Web, applications will need to integrate and aggregate data from multiple source and clean and transform data to facilitate exchange. Data extraction, conversion, transformation, and integration are all well-understood database problems, and their solutions rely on a query language. We present a query language for XML, called XML-QL, which we argue is suitable for performing the above tasks. XML-QL is a declarative, `relational complete' query language and is simple enough that it can be optimized. XML-QL can extract data from existing XML documents and construct new XML documents.     

An object-oriented model for the specification of manufacturing systems

The design of advanced manufacturing systems entails a high flexibility in the system specification method, to allow for flexibility and efficiency in coping with the frequent design modifications. Object-oriented specification methods possess the necessary expressiveness and extensibility to allow for such flexibility. In order to obtain a declarative representation of the knowledge of objects, the semantic data model of the frame-based representation method is incorporated. This extended object-oriented model can be used for specifying system behaviors. Within this model, generic object types representing general concepts in manufacturing systems are identified. These generic object types can facilitate the specification of manufacturing systems by means of an object-oriented approach. The application of the model for system specification is illustrated with reference to a typical robotic FMC.     

Graphical scenarios for specifying temporal properties: an automated approach

Temporal logics are commonly used for reasoning about concurrent systems. Model checkers and other finite-state verification techniques allow for automated checking of system model compliance to given temporal properties. These properties are typically specified as linear-time formulae in temporal logics. Unfortunately, the level of inherent sophistication required by these formalisms too often represents an impediment to move these techniques from “research theory” to “industry practice”. The objective of this work is to facilitate the nontrivial and error prone task of specifying, correctly and without expertise in temporal logic, temporal properties. In order to understand the basis of a simple but expressive formalism for specifying temporal properties we critically analyze commonly used in practice visual notations. Then we present a scenario-based visual language called Property Sequence Chart (PSC) that, in our opinion, fixes the highlighted lacks of these notations by extending a subset of UML 2.0 Interaction Sequence Diagrams. We also provide PSC with both denotational and operational semantics. The operational semantics is obtained via translation into Büchi automata and the translation algorithm is implemented as a plugin of our Charmy tool. Expressiveness of PSC has been validated with respect to well known property specification patterns. Preliminary results appeared in (Autili et al. 2006a).     

Efficient Prolog: a practical tutorial

This tutorial presents twelve guidelines for making Prolog programs efficient. Topics covered include procedural versus declarative programming, internal representation of data, first-argument indexing, cuts, and ways to avoid consing.     

一种基于XML的Web页面定义语言

数据密集(data-intensive)型Web站点是指那些将大量的异构数据源的数据进行集成以后所生成的Web站点.此类站点的建设可以划分为3项主要任务:数据的访问与集成、站点结构的构造(指定各页面所含内容以及各页之间的链接)和页面的HTML表示.以XML以及来自W3C的相关规范为基础,构建了一种Web页面定义语言WPDL(Web page definition language).给出了WPDL的一个简化的EBNF表示,并举例说明了WPDL的关键特性.并且说明,使用这种说明式的查询语言(declarative query language),可以将数据访问、站点结构生成与页面表示彼此分离开来,使站点的重构(restructuring)、重用(reusability)和完整性约束的实施(integrity constraint enforcement)成为可能.     

Rule-based verification of Web sites

In this paper, we develop a framework for the automated verification of Web sites, which can be used to specify integrity conditions for a given Web site, and then automatically check whether these conditions are fulfilled. First, we provide a rewriting-based, formal specification language which allows us to define syntactic as well as semantic properties of the Web site. Then, we formalize a verification technique which detects both incorrect/forbidden patterns as well as lack of information, that is, incomplete/missing Web pages inside the Web site. Useful information is gathered during the verification process which can be used to repair the Web site. Our methodology is based on a novel rewriting-based technique, called partial rewriting, in which the traditional pattern matching mechanism is replaced by tree simulation, a suitable technique for recognizing patterns inside semistructured documents. The framework has been implemented in the prototype GVerdi, which is publicly available.     

Maintenance of a Piercing Set for Intervals with Applications

   Abstract. We show how to maintain efficiently a minimum piercing set for a set S of intervals on the line, under insertions and deletions to/from S. A linear-size dynamic data structure is presented, which enables us to compute a new minimum piercing set following an insertion or deletion in time O(c( S) log |S|), where c (S) is the size of the new minimum piercing set. We also show how to maintain a piercing set for S of size at most (1+ɛ)c (S), for 0 < ɛ ≤ 1 , in

From liveness to promptness

Liveness temporal properties state that something “good” eventually happens, e.g., every request is eventually granted. In Linear Temporal Logic (LTL), there is no a priori bound on the “wait time” for an eventuality to be fulfilled. That is, F θ asserts that θ holds eventually, but there is no bound on the time when θ will hold. This is troubling, as designers tend to interpret an eventuality F θ as an abstraction of a bounded eventuality F ^≤k θ, for an unknown k, and satisfaction of a liveness property is often not acceptable unless we can bound its wait time. We introduce here prompt-LTL, an extension of LTL with the prompt-eventually operator F _p . A system S satisfies a prompt-LTL formula φ if there is some bound k on the wait time for all prompt-eventually subformulas of φ in all computations of S. We study various problems related to prompt-LTL, including realizability, model checking, and assume-guarantee model checking, and show that they can be solved by techniques that are quite close to the standard techniques for LTL.     

Graph regularization methods for Web spam detection

We present an algorithm, witch, that learns to detect spam hosts or pages on the Web. Unlike most other approaches, it simultaneously exploits the structure of the Web graph as well as page contents and features. The method is efficient, scalable, and provides state-of-the-art accuracy on a standard Web spam benchmark.     

Solving Some Discrepancy Problems in NC

We show that several discrepancy-like problems can be solved in NC nearly achieving the discrepancies guaranteed by a probabilistic analysis and achievable sequentially. For example, we describe an NC algorithm that given a set system (X, S) , where X is a ground set and S⊆2 ^X , computes a set R⊆X so that for each S∈ S the discrepancy ||R S|-|R^-∩S|| is . Whereas previous NC algorithms could only achieve discrepancies with ɛ>0 , ours matches the probabilistic bound within a multiplicative factor 1+o(1) . Other problems whose NC solution we improve are lattice approximation, ɛ -approximations of range spaces with constant VC-exponent, sampling in geometric configuration spaces, approximation of integer linear programs, and edge coloring of graphs. Received June 26, 1998; revised February 18, 1999.     

Resource Allocation in Bounded Degree Trees

We study the bandwidth allocation problem (bap) in bounded degree trees. In this problem we are given a tree and a set of connection requests. Each request consists of a path in the tree, a bandwidth requirement, and a weight. Our goal is to find a maximum weight subset S of requests such that, for every edge e, the total bandwidth of requests in S whose path contains e is at most 1. We also consider the storage allocation problem (sap), in which it is also required that every request in the solution is given the same contiguous portion of the resource in every edge in its path. We present a deterministic approximation algorithm for bap in bounded degree trees with ratio . Our algorithm is based on a novel application of the local ratio technique in which the available bandwidth is divided into narrow strips and requests with very small bandwidths are allocated in these strips. We also present a randomized (2+ε)-approximation algorithm for bap in bounded degree trees. The best previously known ratio for bap in general trees is 5. We present a reduction from sap to bap that works for instances where the tree is a line and the bandwidths are very small. It follows that there exists a deterministic 2.582-approximation algorithm and a randomized (2+ε)-approximation algorithm for sap in the line. The best previously known ratio for this problem is 7. A preliminary version of this paper was presented at the 14th Annual European Symposium on Algorithms (ESA), 2006.     

Definite clause programs are canonical (over a suitable domain)

For each first-order languageL with a nonempty Herbrand universe, we construct an algebraC interpreting the function symbols ofL that is a model of the Clark equality theory with languageL and is canonical in the sense that for every definite clause programP in the languageL,T _P ^C is the greatest fixed point ofT _P ^C . The universe of individuals inC is a quotient of the set of terms ofL and is, a fortiori, countable ifL is countable. If contains at least one function symbol of arity at least 2, then the graphs of partial recursive functions onC, suitably defined, are representable in a natural way as individuals inC.Research sponsored in part by U.S. Air Force Contract F30602-85-C-0008.