Distributed event-based systems pdf

The service operations map to features, operation pa- subscription manager is responsible for managing rameters map to data concepts, etc. As a result, subscriptions which are put into the subscription services that perform the same task but have dif- storage. In addition, subscriptions are translated ferent interfaces can be dynamically replaced at for further processing. This is done by converting runtime. The Esper engine performs the actual event vResCo eventing engine processing and is, therefore, responsible for match- ing incoming events received from the eventing This section presents the VRESCo notification service to listeners attached by the subscription support that was introduced in Michlmayr, manager.

The basic listener informs the notification manager that is idea can be summarized as follows: notifications responsible for notifying interested subscribers. The event database is imple- Other event types include runtime information mented using a relational database and accessed concerning binding and invocation, querying in- via the ORM layer.

The querying service returns formation and user information. All events inherit a list of events that match the given query. The first step in developing such notification Event Participants mechanism is to define all events supported by the engine.

In the context of our work there are Event-based systems usually consist of two types several events that can be captured at runtime. We of participants that pose different requirements have identified the events shown in Table 1 where to the system, namely event producers and event events are grouped according to their event type.

The event condition in the right column describes In general, events are produced by VRESCo the situations when the event occurs. These event components. However, different components are types form an event type hierarchy following the responsible for firing different kinds of events. In this is illustrated using colons. As a result, outside the runtime. Most events are directly pro- the events concerning binding and invocation e.

ServiceInvokedEvent are fired by this component. For instance, service management events e. The same is true for versioning and and invocation events into the runtime. These cli- metadata events. According to this, user manage- ent events represent external events that are then ment events are published by the user manage- transformed into the internal event format by the ment service while querying events are produced runtime.

Finally, the QoS monitor that regularly by the querying service. All these event types measures the QoS values of services is responsible have in common that they are produced as part for firing QoS events. Similar to the client library, of the VRESCo services and therefore represent the QoS monitor uses the notification interface to internal events. The application logic inherent to binding and Similar to event producers, we distinguish invocation of services is located in the service between internal and external consumers.

In the latter case, one subscriptions match incoming events. External problem might be that event producers consumers outside the runtime are notified depend- do not know the importance of particular ing on the notification delivery mode defined in events related to others.

Clearly, most important event while the leaves are notification delivery mechanisms and the notifica- less important.

That means each event email, SMS or news feeds. In some scenarios, has a specific type possibly supporting it might also be suitable to log the occurrence type inheritance that is used to define the of events in log files that are regularly checked ranking.

However, the importance of some by the system administrator. In any case, notifi- event might not always depend only on its cations for humans might be less explicit since type — sometimes the event properties will humans can interpret incomplete information.

In make the difference. For our current e. Moreover, another distinction can be made In this regard, one can assume that frequent between service providers and consumers that events e. For be less important than infrequent ones instance, service consumers might not be interested e.

We introduce different occur as part of event patterns e. The Event Ranking ranking mechanism could consider such event patterns. The importance and relevance of different events can be estimated by ranking them according to VRESCo supports hierarchically, priority-, some fitness function.

This is of particular interest typed-, and content-based ranking. Probability- when dealing with vast numbers of events. The based ranking could be integrated by using the following list describes several ways we have univariate statistic function provided by Esper. Yet, introducing event ranking related. Furthermore, users are often interested in mechanisms provides different ways to express all events that occurred within a given timeframe.

To accomplish temporal correlation of events, every event has a timestamp that is set during Event Correlation event publication. This timestamp can then be used to group events that happened within a given Event-based systems usually deal with vast num- period of time e.

Event correlation techniques are used to avoid The difference between event correlation sets losing track of all events and their relationship. For related due to some event attribute e. Subscription and Notification In the context of our work, we have identified Mechanism a number of correlation sets summarized in Table 2, which shows the name of the correlation set, the In general, event consumers can be enabled to events that are subsumed in this correlation, and subscribe to their events of interest in several ways the correlation identifier.

Event service revision lifecycle and QoS using ServiceId consumers subscribe to receive notifications about and ServiceRevisionId, and metadata information that topic. Even though these two styles are simple, e. This is important events of interest. Esper listener. This listener is finally attached to Since the VRESCo runtime is provided using the Esper engine to be matched against incoming Web service interfaces, the subscription interface events.

Furthermore, the subscription manager should also be using Web services. WS-Eventing is responsible for keeping the subscriptions in represents a light-weight specification that defines the storage and the listeners attached to Esper such an interface by providing five operations: synchronized.

That means, when subscriptions Subscribe and Unsubscribe are used for subscrib- are renewed or expire, the subscription manager ing and unsubscribing. The GetStatus operation re-attaches the corresponding listener or removes returns the current status of a subscription, while them, respectively.

Renew is used to renew existing subscriptions. Sending notifications can be done in several Each subscription has a given duration specified ways. Finally, Subscription End In the best-effort model, notifications are lost is used if an event source terminates a subscrip- in case of communication errors.

To prevent such tion unexpectedly. Besides pushing mechanism of the VRESCo runtime, we build notifications towards subscribers, pull-style no- upon an existing WS-Eventing implementation3 tifications enable subscribers to retrieve pending that was extended for our purpose.

WS-Eventing notifications from the event engine. As shown in ing XML messages to stored subscriptions. The Figure 7, the notification manager knows which specification defines an extension point to use notification type to use depending on the listener other filter dialects which we used to introduce the attached to the Esper engine.

The actual EPL query is then attached this information from the listener. If the event to the subscription message by introducing a new sink prefers email notifications, the notification message attribute subscriptionQuery.

In case of WS-Eventing distinguishes between subscrib- Web service listeners, the notification manager er the entity that defines a subscription and event invokes the corresponding listener Web service sink the entity that receives the notifications provided by the event sink. They cover the complete spectrum of topics, ranging from a treatment of local event matching and distributed event forwarding algorithms, through a more practical discussion of software engineering issues raised by the event-based style, to a presentation of state-of-the-art research topics in event-based systems, such as composite event detection and security.

Their presentation gives researchers a comprehensive overview of the area and lots of hints for future research. In addition, they show the power of event-based architectures in modern system design, thus encouraging professionals to exploit this technique in next generation large-scale distributed applications like information dissemination, network monitoring, enterprise application integration, or mobile systems.

It is largely self-contained and the exposition is meticulous and rigorous. Altogether, this book is a great enrichment to the existing texts on the subject, and it deserves a wide audience.

Principles and Applications of Distributed Event-Based Systems showcases event-based systems in real-world applications. Containing expert international contributions, this advanced publication provides professionals, researchers, and students in systems design with a rich compendium of latest applications in the field. Distributed Event-based Systems.

Saptharishi, M. Schmidt, K. Schwiderski-Grosche, S. Seufert, A. Soh, L. Tanenbaum, A. Principles and paradigms, 2nd edn. Turchin, Y. Verginadis, Y. Vijayakumar, N. In: Ganguly, A. Knowledge Discovery From Sensor Data, pp. In: Gokhale, A. Xhafa, F. Zaera, M.

University of Zaragoza August Google Scholar. Zhao, S. Multi-media Computing and Networking Conf. Zhuang, S. University Politehnica of Bucharest Bucharest Romania.

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