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ComputerAided_Design_Engineering_amp_Manufactur.pdf

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ule is violated, a warning should be issued to the designer to request either deletion of this new path or<br />

addition of more PSPs. In order to automate this process, a mechanism is needed to<br />

• Record the relationship between any two PSPs,<br />

• Determine the applicable rule upon a path generation, and generate additional paths and entries,<br />

if necessary, or, if no rules are applicable, delete this path.<br />

We use matrix to perform the first function. Instead of recording connectivity between places and<br />

transitions, the matrix in our algorithm records structural relationship between PSPs. Before a path is<br />

generated, the T-Matrix needs to be consulted to verify that no rule is violated. Whenever a new path is<br />

created, a PSP may be separated into several new PSPs, and relationships between some PSPs are changed.<br />

Therefore, the total number of PSPs needs to be updated, as do the matrix entries.<br />

Ex<strong>amp</strong>le: Figure 8.4(a) shows a PN model with its matrix shown in Figure 8.4(b). Originally there are<br />

five PSPs in solid paths �1 to �5 ; �6 in a dashed path is to be added by IG. �1 is concurrent to all<br />

other PSPs. Therefore, all entries in the first column and the first row are CN. �2 and �3 are exclusive<br />

to each other, as are and . Therefore,<br />

� 6<br />

� 4<br />

� 5<br />

Notice returns to form cycles; therefore, some entries need to be updated. Prior to generation,<br />

�3 is structurally sequentially earlier (SE) to both �4 and �5 . After the addition, �6 , �4 , and �5 become SE to �3 , implying the formation of cycles.<br />

We have described how the T-Matrix records the relationship. The next section presents the algorithm<br />

and the associated time complexity for updating the T-matrix.<br />

8.5 The Algorithm and Its Complexity<br />

The algorithm consists of two steps:<br />

A23 � A32 � A45 � A54 � EX.<br />

1. Create new entries in the T-Matrix for each NP.<br />

2. Determine the applicable rule; generate additional NPs if necessary and update the T-Matrix<br />

accordingly. If no rule is applicable or some rules are violated, delete the path.<br />

For ex<strong>amp</strong>le, if a PP-path is generated between pg and pj and pg � pj , then Rule PP.0 dictates that<br />

this path should be deleted. It is easy to find the structural relationship between the new PSP � and<br />

the PSPs directly involved with the generation, but not obvious as to the structural relationship between<br />

PSPs far away from (no direct connection with) the . In the following, we will develop techniques for<br />

new entries for PG and IG, respectively.<br />

w<br />

� w<br />

Determination of Entries for Pure-Generation<br />

After the PG of a �l from �g, �g is split into three new PSPs: �g1 → �g2 → �g3. The entries related<br />

to should be deleted. The values for the new entries are<br />

� g<br />

A�ik � Agk, A�ki � Akg where �k is any PSP other than �g, �l, �g1, �g2 and �g3 , and �i is one of the newly created PSPs. Note<br />

that �g1 and/or �g2 may be empty. The other new entries are the relationships among the newly created<br />

PSPs:<br />

A� g2 g 1<br />

A� g1 g 2<br />

� � �<br />

A� g3 g 1<br />

A� g2 g 3<br />

A� g3 g 2<br />

A� g1 g 3<br />

SL,<br />

� � �<br />

SE<br />

� 6

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