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2 The Language: Rationale and Fundamentals 69
2.5.3 Link Conditions

As a consequence of a fully ﬂedged data perspective, YAWL is able to support
conditions (known as link or ﬂow conditions) on outgoing arcs from OR-splits
and XOR-splits. These conditions take the form of XPath expressions, which
evaluate to a Boolean result, indicating whether the thread of control can be
passed to this link or not. For OR-splits, all outgoing link conditions are evalu-
ated and the thread of control is passed to all that evaluate to true. A default link
is nominated to which the thread of control is passed if none of the link con-
ditions evaluate to true. For XOR-splits, the link conditions are evaluated in a
speciﬁed evaluation sequence and once the ﬁrst link condition evaluates to true,
then the thread of control is passed to that link and any further evaluation of
link conditions ceases. If none of the link conditions evaluate to true, then the
thread of control is passed to the link that is last in the evaluation sequence.
Figure 2.31 illustrates the conﬁguration of the ﬂow conditions for the XOR-split
associated with the Practical Test task in the Driving Test Process shown earlier in
Fig. 2.23.

Fig. 2.31 Link condition speciﬁcation in YAWL

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