Mumbai University > Computer engineering > Sem 7 > Software Architecture.

Marks: 10 M

Year: May 12

An event is defined as the instantaneous effect of the termination of an operation on the object, which occurs at that objects location. Event connectors affect the flow of control among components, thus provide co-ordination services. When an event connector learns about the occurrence of an event, it generates messages for all interested parties and yields control to the components for processing those messages. The contents of an event can be structured to contain information like time and place of occurrence and application specific data. Thus, event connectors also provide communication service.

Here, virtual connectors are formed between components interested in the same event topics and those connectors may appear and disappear dynamically depending on the components’ changing interests.

The variation dimensions of an event connector are shown below:

The different dimensions of Event connectors are

• Cardinality which has the sub dimensions Producers, Observers and Event patterns.
• Delivery dimension can take values best effort, exactly once, at most once and at least once.
• Priority has sub dimensions incoming and outgoing.
• Synchronicity dimension can take values like synchronous, asynchronous and time out synchronous.
• Notification dimension has values polled, publish/subscribe, central update and queued dispatch.
• Causality dimension can take values absolute and relative.
• Mode has dimensions hardware and software, where hardware can take values like page faults, interrupts and traps, software can take values signals, GUI input/output and triggers.

Event based distributed systems rely on the notion of time and ordering of actions. Therefore, dimensions such as causality, atomicity and synchronicity play a critical role in event connector mechanism. Event connectors are found in distributed applications that require asynchronous communication. An example is a windowing application where GUI input serves the event that activates the system. Some events such as page faults, interrupts and traps are triggered by hardware and then processed by software. The cardinality of a multicasting event connector will be a single producer and multiple observer components, also the connector will support delivery of data exactly once; its synchronicity may be asynchronous and it could use publish/subscribe notification mechanism.