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Purpose

In order to be able to retrieve event histories, we maintain a persistent store of events received over the event bus linking clients, services and containers. This store is provided with a simple (Axis) web-service façade (no authentication required).

The position of this repository service can be seen in the events & messaging diagram as the "Simple Event Store"; the implementation of the service subscribes to the bus and stores all events sent over it.

A special query object is used to retrieve sets of events. There are also ports on the service for removing matching events and for writing out matching events to a log file.

Mode of Usage

In most cases, the user will interact with this service through specially designed Siege views (refer to the tutorial for specifics). Programmatic interactions also take place via the web service ports from the Workflow Broker when cleanup or archive routines are called. A brief description of the API follows.

API

Service WSDL

EventRepository

removeNoReply is useful when cleaning up the database (returning all events will with a high probability generate an out-of-memory error in the client).

The return value of the logEvents method is the URL where the log file may be found.


EventDescriptor

A simple wrapper around the LocalEvent object. Class name identifies the type of local event (necessary for deserialization).


EventQuery

A simplified version of the LocalEventFilter: it corresponds to a single ncsa.tools.events.types.filters.LocalEventHeaderComparator, a conjunction of comparisons on the header properties represented by the set- and get- methods. The lastId field is used by the service client for more scalable pulls (there is a default batch size of 100 events at a time).

A subclass of EventQuery, ncsa.services.events.utilities.EventQueryAdapter, allows for conversion between this object and a LocalEventFilter as well as providing several flags useful for interaction with the service (for instance, it is often the case that one will wish to receive all events generated up to this point in time, but to continue listening for incoming events matching that filter as well); this utility class, in fact, is used under the covers by several Siege views.

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