A computer system comprising: a buffer configured to store a plurality of items (114a, 114b, 114c), and configured to be accessed by one or more activities (104, 106, 108, 110) of an instance of a process model; a scheduler configured to schedule execution of each of a plurality of activities (104, 106, 108, 110) of the process model, and configured to determine an activation of an activity (104, 106, 108, 110) of the plurality of activities (104, 106, 108, 110), the scheduler including a process execution unit configured to execute the activity (104, 106, 108, 110), characterized in, that the scheduler further includes an activity manager configured to access an activity profile of the activity (104, 106, 108, 110) upon the determining of the activation, the activity profile including buffer access characteristics according to which the activity (104, 106, 108, 110) is designed to access the buffer, wherein activity profiles are associated with activities (104, 106, 108, 110); and the process execution unit including a buffer access manager configured to access the buffer according to the buffer access characteristics of the activity profile, and to thereby facilitate an exchange of at least one item between the buffer and the activity (104, 106, 108, 110) during the execution of the activity (104, 106, 108, 110) by generating a temporary buffer that may store a first subset of data items from the buffer that may be needed by a particular activity (104, 106, 108, 110), and by generating another such temporary buffer storing a second subset of data items that may be needed by another activity (104, 106, 108, 110). a buffer configured to store a plurality of items (114a, 114b, 114c), and configured to be accessed by one or more activities (104, 106, 108, 110) of an instance of a process model; a scheduler configured to schedule execution of each of a plurality of activities (104, 106, 108, 110) of the process model, and configured to determine an activation of an activity (104, 106, 108, 110) of the plurality of activities (104, 106, 108, 110), the scheduler including a process execution unit configured to execute the activity (104, 106, 108, 110), characterized in, that the scheduler further includes an activity manager configured to access an activity profile of the activity (104, 106, 108, 110) upon the determining of the activation, the activity profile including buffer access characteristics according to which the activity (104, 106, 108, 110) is designed to access the buffer, wherein activity profiles are associated with activities (104, 106, 108, 110); and the process execution unit including a buffer access manager configured to access the buffer according to the buffer access characteristics of the activity profile, and to thereby facilitate an exchange of at least one item between the buffer and the activity (104, 106, 108, 110) during the execution of the activity (104, 106, 108, 110) by generating a temporary buffer that may store a first subset of data items from the buffer that may be needed by a particular activity (104, 106, 108, 110), and by generating another such temporary buffer storing a second subset of data items that may be needed by another activity (104, 106, 108, 110).