We discuss the design of an acquisitional query processor for data collection in sensor networks. Acquisitional issues are those that pertain to where, when, and how often data is physically acquired (sampled) and delivered to query processing operators. By focusing on the locations and costs of acquiring data, we are able to significantly reduce power consumption over traditional passive systems that assume the a priori existence of data. We discuss simple extensions to SQL for controlling data acquisition, and show how acquisitional issues influence query optimization, dissemination, and execution. We evaluate these issues in the context of TinyDB, a distributed query processor for smart sensor devices, and show how acquisitional techniques can provide significant reductions in power consumption on our sensor devices.

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The design of an acquisitional query processor for sensor networks

A large number of distributed applications requires continuous and timely processing of information as it flows from the periphery to the center of the system. Examples include intrusion detection systems which analyze network traffic in real-time to identify possible attacks; environmental monitoring applications which process raw data coming from sensor networks to identify critical situations; or applications performing online analysis of stock prices to identify trends and forecast future values.Traditional DBMSs, which need to store and index data before processing it, can hardly fulfill the requirements of timeliness coming from such domains. Accordingly, during the last decade, different research communities developed a number of tools, which we collectively call Information flow processing (IFP) systems, to support these scenarios. They differ in their system architecture, data model, rule model, and rule language. In this article, we survey these systems to help researchers, who often come from different backgrounds, in understanding how the various approaches they adopt may complement each other.In particular, we propose a general, unifying model to capture the different aspects of an IFP system and use it to provide a complete and precise classification of the systems and mechanisms proposed so far.

Processing flows of information: From data stream to complex event processing

In this paper, we present the design, implementation, and evaluation of a system that executes complex event queries over real-time streams of RFID readings encoded as events. These complex event queries filter and correlate events to match specific patterns, and transform the relevant events into new composite events for the use of external monitoring applications. Stream-based execution of these queries enables time-critical actions to be taken in environments such as supply chain management, surveillance and facility management, healthcare, etc. We first propose a complex event language that significantly extends existing event languages to meet the needs of a range of RFID-enabled monitoring applications. We then describe a query plan-based approach to efficiently implementing this language. Our approach uses native operators to efficiently handle query-defined sequences, which are a key component of complex event processing, and pipeline such sequences to subsequent operators that are built by leveraging relational techniques. We also develop a large suite of optimization techniques to address challenges such as large sliding windows and intermediate result sizes. We demonstrate the effectiveness of our approach through a detailed performance analysis of our prototype implementation under a range of data and query workloads as well as through a comparison to a state-of-the-art stream processor.

/pdf/high-performance-complex-event-processing-over-streams-24vc8wfi8x.pdf

High-performance complex event processing over streams

Active database systems support mechanisms that enable them to respond automatically to events that are taking place either inside or outside the database system itself. Considerable effort has been directed towards improving understanding of such systems in recent years, and many different proposals have been made and applications suggested. This high level of activity has not yielded a single agreed-upon standard approach to the integration of active functionality with conventional database systems, but has led to improved understanding of active behavior description languages, execution models, and architectures. This survey presents the fundamental characteristics of active database systems, describes a collection of representative systems within a common framework, considers the consequences for implementations of certain design decisions, and discusses tools for developing active applications.

/pdf/active-database-systems-1g8cqg5by3.pdf

Active database systems

Current workflow management systems still lack support for dynamic and automatic workflow adaptations. However, this functionality is a major requirement for next-generation workflow systems to provide sufficient flexibility to cope with unexpected failure events. We present the concepts and implementation of AGENTWORK, a workflow management system supporting automated workflow adaptations in a comprehensive way. A rule-based approach is followed to specify exceptions and necessary workflow adaptations. AGENTWORK uses temporal estimates to determine which remaining parts of running workflows are affected by an exception and is able to predictively perform suitable adaptations. This helps to ensure that necessary adaptations are performed in time with minimal user interaction which is especially valuable in complex applications such as for medical treatments.

/pdf/agent-work-a-workflow-system-supporting-rule-based-workflow-36171zptma.pdf

AGENT WORK: a workflow system supporting rule-based workflow adaptation

This paper presents some of the advantages accrued from adopting an object-oriented (OO) data model versus the relational data model when representing and managing a Vector Product Format (VPF) database, specifically the Digital Nautical Chart (DNC) for Norfolk Harbor, Virginia. An OO-DNC prototype viewer capable of importing, displaying and editing DNC feature data both from relational-format and from object-format files was developed using the Smalltalk language. The differences in performance between the relational import and the object import were then compared across several DNC coverages. The results indicate a significant increase in performance when adopting the OO paradigm; specifically the OO-DNC viewer imported feature data from object-format files from 6 to 15 times faster than from the relational-format files. It should be noted that these figures are NOT the result of comparing a commercial object-oriented database managment system (ODBMS) against a commercial relational database management system (RDBMS), but rather the result of reading both relational-oriented and object-oriented data file formats using an object-oriented program written in Smalltalk. Nevertheless, we feel these results indicate a significant functionality and performance improvement can be obtained by using an OO framework for the data and software.

Comparison and Benchmarks for Import of VPF Geographic Data from Object-Oriented and Relational Database Files

Use of databases for non-traditional applications has prompted the development of an array of new transaction models whose semantics vary from the traditional model as well as from each other. The implementation details of most of the proposed models have been sketchy at best. Furthermore, current architectures of most DBMSs do not lend themselves to supporting more than one built-in transaction model. As a result, despite the presence of rich transaction models, applications cannot realize semantics other than that provided by the traditional transaction model.
In this dissertation, we propose a framework for supporting various transaction models in an extensible manner. We demonstrate how ECA (event-condition-action) rules, defined at the system level on significant operations of a transaction and/or data structures such as a lock table, allow the database implementor/customizer to support: (i) currently proposed extended transaction models, and (ii) newer transaction models as they become available. Most importantly, this framework allows one to customize transaction (or application) semantics in arbitrary ways using the same underlying mechanism. Sentinel, an active object-oriented database system developed at UF, is used for demonstrating our approach for implementing extended transaction models.

An extensible approach to realizing extended transaction models

: Over the last few years active databases have become an important research area geared towards meeting of the requirements of a variety of non- traditional applications. This report concentrates on providing a seamless incorporation of events and rules into an OODBMS with an emphasis on the modularity and extensibility of the resulting system. The report extends the monitoring view point to an external one, thereby allowing objects to monitor and react to changes occurring to their own state as well as changes occurring to other objects. This is accomplished by introducing a reactive asynchronous object interface. This interface enables objects to propagate pre-declared events occurring to their state to other objects, thereby enabling other objects to perform operations. In addition, a subscription and notification mechanism is introduced that allows event notification to be specified dynamically. This mechanism enables objects to selectively monitor other objects at run-time using the reactive interface. A design is proposed for the specification and detection of simple as well as complex events. This report combines the strengths of the approaches taken in Ode and ADAM and extends them in several significant ways.

/pdf/active-database-architectures-and-the-design-of-sentinel-for-tf8z2qtt4t.pdf

Active Database Architectures and the Design of Sentinel for Constraint Management

This paper proposes a new approach for supporting reactive capability in an object-oriented database. We introduce an event interface, which extends the conventional object semantics to include the role of an event generator. This interface provides a basis for the specification of events spanning sets of objects, possibly from different classes, and detection of primitive and complex events. This approach clearly separated event detection from rules. New rules can be added and use existing objects, enabling objects to react to their own changes as well as to the changes of other objects.We use a runtime subscription mechanism, between rules and objects to selectively monitor particular objects dynamically. This elegantly supports class level as well as instance level rules. Both events and rules are treated as first class objects.

/pdf/a-new-perspective-on-rule-support-for-object-oriented-4xs0swk5rv.pdf

A new perspective on rule support for object-oriented databases

Making a database system active entails developing an expressive event specification language with well-defined semantics, algorithms for the detection of composite events, and an architecture for an event detector along with its implementation. Thii paper presents the semantics of composite events using the notion of a global event history (or a global event-log). Parameter contexts are introduced and precisely defined to facilitate efficient management and detection of composite events. Finally, an architecture and the implementation of a composite event, detector is analyzed in the context of an object-oriented active DBMS.

Composite Events for Active Databases: Semantics, Contexts and Detection

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