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Distributed systems are computer systems that are connected by a communication network or any technology that features by the delay in its communication. In addition, these systems present absence of a share clock and shared memory. As a consequence of these absences, it is not easy to observe the order of a distributed system execution trace because events (eg. sending and receiving of messages) generates by computer systems are not always causally related. There are algorithms that are able to determine the causal relation between two events, therefore, these algorithms can partially determine the order of a distributed system execution trace. The vector clock algorithm is widely used to observe the order of a distributed system execution trace.
Example of a system of vector clocks (wikipedia)
As OTM supports the definition of entities that observe and react to a Web application execution trace, we have extended our prototype to observe and react to distributed execution traces using the vector clock algorithm. Next, we present two examples, where OTM observes distributed execution traces that present in social Web applications like Twitter or Google Reader. The examples show the use of OTM+vector clocks to analysis flows of information between actors instead of the use of dynamic graphs 1).
- Popularity of a piece of news: This example determines the popularity of a piece of news that somebody publishes.
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