r ones. For example, in Figure 5.60, the sequence sA, sB, sC, sD is split into sA, sB and sC, sD. observer MSC equivalent MSC and_1 inst_1 test_1 test_2 proc1 test_1 test_2 inst_1 inst_1 proc1 proc1 Figure 5.60 The operator AND The operator OR means that the expected behavior is an alternative between two or more MSCs. For example, in Figure 5.61, the expected behavior is: either the sequence sA, sB or the sequence sA, sC. observer MSC equivalent MSCs res 1 inst_1 Named + in proc1 Framework test_1 test_3 test_1 inst_1 test_3 inst_1 res_1 inst_1 proc1 proc1 proc1 Figure 5.61 The operator OR This example also illustrates the fact that there can be a common part between several MSCs under an OR operator (here, sA is common to test_1 and test_3). 152 Validation of Communications Systems with SDL The operator REPEAT means that the expected behavior is the repetition from 0 to n times of an MSC. For example, in Figure 5.62, the expected behavior is: either nothing, or the sequence sA, sB, sC, or the sequence sA, sB, sC, sA, sB, sC, and SO on. observer MSC 0 repetition: equivalent MSCs res_1 test_loop inst_1 2 repetitions: proc1 res_3 inst_1 test_2 proc1 1 repetition: test_2 inst_1 res 2 proc1 inst_1 proc1 Figure 5.62 The operator REPEAT 5.3.4.2 The MSC symbols used for observation When an MSC is compiled with an SDL model, ObjectGeode checks that: All the elements used in the MSC exist in the SDL model. The scope in the MSC is compatible with the SDL model. For example, in Figure 5.63, the following checks are performed during compilation: The entity named dataLink in the MSC retry1 exists in the SDL model HDLC. The signal v76frame in the MSC also exists in the SDL model. system HDLC ch1 retry1 inst_DL v76frame ] datalink datalink v76frame (sabme : (.0.)) SIGNAL v76frame(v76_par); Figure 5.63 An MSC (b) consistent with the SDL model (a) Automatic Observation of Simulations 153 The signal v76frame being received by dataLink in the MSC, a channel carrying v76frame and reaching dataLink exists in the SDL model. The name i