RDF Querying

Reactive Web systems, Web services, and Web-based publish/ subscribe systems communicate events as XML messages, and in many cases require composite event detection: it is not sufficient to react to single event messages, but events have to be considered in relation to other events that are received over time. Emphasizing language design and formal semantics, we describe the rule-based query language XChangeEQ for detecting composite events. XChangeEQ is designed to completely cover and integrate the four complementary querying dimensions: event data, event composition, temporal relationships, and event accumulation. Semantics are provided as model and fixpoint theories; while this is an established approach for rule languages, it has not been applied for event queries before

Completing Queries: Rewriting of IncompleteWeb Queries under Schema Constraints

Reactive Web systems, Web services, and Web-based publish/ subscribe systems communicate events as XML messages, and in many cases require composite event detection: it is not sufficient to react to single event messages, but events have to be considered in relation to other events that are received over time. Emphasizing language design and formal semantics, we describe the rule-based query language XChangeEQ for detecting composite events. XChangeEQ is designed to completely cover and integrate the four complementary querying dimensions: event data, event composition, temporal relationships, and event accumulation. Semantics are provided as model and fixpoint theories; while this is an established approach for rule languages, it has not been applied for event queries before

Twelve Theses on Reactive Rules for the Web

Reactivity, the ability to detect events and respond to them automatically through reactive programs, is a key requirement in many present-day information systems. Work on Web Services re ects the need for support of reactivity on a higher abstraction level than just message exchange by HTTP. This article presents the composite event query facilities of the reactive rule-based programming language XChange. Composite events are important in the dynamic world of the Web where applications, or Web Services, that have not been engineered together are composed and have to cooperate by exchanging event messages

Rule-Based Composite Event Queries

Reactive Web systems, Web services, and Web-based publish/ subscribe systems communicate events as XML messages, and in many cases require composite event detection: it is not sufficient to react to single event messages, but events have to be considered in relation to other events that are received over time. Emphasizing language design and formal semantics, we describe the rule-based query language XChangeEQ for detecting composite events. XChangeEQ is designed to completely cover and integrate the four complementary querying dimensions: event data, event composition, temporal relationships, and event accumulation. Semantics are provided as model and fixpoint theories; while this is an established approach for rule languages, it has not been applied for event queries before

Reactivity on the Web

Reactivity, the ability to detect simple and composite events and respond in a timely manner, is an essential requirement in many present-day information systems. With the emergence of new, dynamic Web applications, reactivity on the Web is receiving increasing attention. Reactive Web-based systems need to detect and react not only to simple events but also to complex, real-life situations. This paper introduces XChange, a language for programming reactive behaviour on the Web, emphasising the querying of event data and detection of composite events

NEEL+: Supporting Predicates for Nested Complex Event Processing

Complex event processing (CEP) has become increasingly important in modern applications, ranging from supply chain management for RFID tracking to real-time intrusion detection. These monitoring applications must detect complex event pattern sequences in event streams. However, the state-of-art in the CEP literature such as SASE, ZStream or Cayuga either do not support the specification of nesting for pattern queries altogether or they limit the nesting of non-occurrence expressions over composite event types. A recent work by Liu et al proposed a nested complex event pattern expression language, called NEEL (Nested Complex Event Language), that supports the specification of the non-occurrence over complex expressions. However, their work did not carefully consider predicate handling in these nested queries, especially in the context of complex negation. Yet it is well-known that predicate specification is a critical component of any query language. To overcome this gap, we now design a nested complex event pattern expression language called NEEL+, as an extension of the NEEL language, specifying nested CEP queries with predicates. We rigorously define the syntax and semantics of the NEEL+ language, with particular focus on predicate scoping and predicate placement. Accordingly, we introduce a top-down execution paradigm which recursively computes a nested NEEL+ query from the outermost query to the innermost one. We integrate predicate evaluation as part of the overall query evaluation process. Moreover, we design two optimization techniques that reduce the computation costs for processing NEEL+ queries. One, the intra-query method, called predicate push-in, optimizes each individual query component of a nested query by pushing the predicate evaluation into the process of computing the query rather than evaluating predicates at the end of the computation of that particular query. Two, the inter-query method, called predicate shortcutting, optimizes inter-query predicate evaluation. That is, it evaluates the predicates that correlate different query components within a nested query by exploiting a light weight predicate short cut. The NEEL+ system caches values of the equivalence attributes from the incoming data stream. When the computation starts, the system checks the existence of the attribute value of the outer query component in the cache and the predicate acts as a shortcut to early terminate the computation. Lastly, we conduct experimental studies to evaluate the CPU processing resources of the NEEL+ System with and without optimization techniques using real-world stock trading data streams. Our results confirm that our optimization techniques when applied to NEEL+ in a rich variety of cases result in a 10 fold faster query processing performance than the NEEL+ system without optimization

Use-cases on evolution

This report presents a set of use cases for evolution and reactivity for data in the Web and Semantic Web. This set is organized around three different case study scenarios, each of them is related to one of the three different areas of application within Rewerse. Namely, the scenarios are: “The Rewerse Information System and Portal”, closely related to the work of A3 – Personalised Information Systems; “Organizing Travels”, that may be related to the work of A1 – Events, Time, and Locations; “Updates and evolution in bioinformatics data sources” related to the work of A2 – Towards a Bioinformatics Web

Complex Actions for Event Processing

Automatic reactions triggered by complex events have been deployed with great success in particular domains, among others, in algorithmic trading, the automatic reaction to realtime analysis of marked data. However, to date, reactions in complex event processing systems are often still limited to mere modifications of internal databases or are realized by means similar to remote procedure calls. In this paper, we argue that expressive complex actions with support for composite work ows and integration of so called external actions are desirable for a wide range of real-world applications among other emergency management. This article investigates the particularities of external actions needed in emergency management, which are initiated inside the event processing system but which are actually executed by external actuators, and discuss the implications of these particularities on composite actions. Based on these observations, we propose versatile complex actions with temporal dependencies and a seamless integration of complex events and external actions. This article also investigates how the proposed integrated approach towards complex events and complex actions can be evaluated based on simple reactive rules. Finally, it is shown how complex actions can be deployed for a complex event processing system devoted to emergency management

Twelve Theses on Reactive Rules for the Web

Reactivity, the ability to detect and react to events, is an essential functionality in many information systems. In particular, Web systems such as online marketplaces, adaptive (e.g., recommender) systems, and Web services, react to events such as Web page updates or data posted to a server. This article investigates issues of relevance in designing high-level programming languages dedicated to reactivity on the Web. It presents twelve theses on features desirable for a language of reactive rules tuned to programming Web and Semantic Web applications