1. A computer program product, tangibly embodied in a machine readable storage device, the computer program product comprising instructions operable to cause data processing apparatus to perform operations comprising: receiving a plurality of process data items associated with a plurality of process instances that are executed using a plurality of components operating in a distributed computer system, each process data item comprising a plurality of application data and having been collected by each agent of a plurality of agents, wherein the plurality of components includes a first set of components that execute a first process instance and a second set of components that execute a second process instance with at least one of the plurality of components included in each of the first and second sets of components, a first agent collecting a first process data item of a first type corresponding to a first attribute and a second attribute, and a second agent collecting a second process data item of a second type corresponding to the first attribute and the second attribute, the first type being different from the second type; comparing in accordance with a plurality of predefined rules each received process data item with one or more other received process data items to identify process data corresponding to process instances executed on the distributed computer system, the predefined rules comprising: identifying the first and second process data items as belonging to a common process instance when a value of the first attribute is equal for both the first and second process data items, identifying the first and second process data items as belonging to a common process instance when values of the first and second attributes are equal for both the first and second process data items, and identifying the first process data item and a third process data item collected by a third agent as belonging to a common process instance when the first and second process data items belong to a common process instance and the second and third process data items belong to a common process instance; grouping into a first group a plurality of process data items corresponding to the first process instance, the first process instance being a single execution of a first sequence of related steps carried out in the distributed computer system; grouping into a second group a plurality of process data items corresponding to the second process instance, the second process instance being a single execution of a second sequence of related steps carried out in the distributed computer system; and reconstructing the first and second process instances based on the process data items in the first and second groups, respectively.