6.2 The Data and Event Flow Diagram Editor (TDEFD)

TDEFD is a proper superset of TDFD. The features that are specific for TDEFD are explained in this section. In short, TDEFD is TDFD extended with control processes and event flows. All nodes and edges of TDFD are available in TDEFD and all constraints in TDFD are applicable to TDEFD. It is also possible to read a .dfd diagram into TDEFD (although a warning is given). The other way around, reading a .defd diagram in TDFD, is only possible when it does not contain event flows or control processes.

6.2.1 Nodes and Edges

TDEFD has data processes and control processes , represented by a solid and a dashed circle, respectively. Both types of nodes have possibly an index label, see section 6.1.3. TDEFD has two types of flows: time discrete flows and time continuous flows. Time discrete flow are the same flows as in TDFD, but time continuous flows are new and they are represented by a double headed arrow (two heads on the same side).

TDEFD has event flows that are represented by dashed arrows. When an event flow has as label `T', it is a trigger and when it has as label `E' or `E/D', it is a prompt . Event flows have a time discrete variant and a time continuous variant too, represented by a dashed single headed arrow respectively by a dashed double headed arrow.

See figure 6.8 for the permitted connections in the data and event flow diagram editor.

**Figure 6.7:** *Data and event flow diagram nodes and edges.*
$\begin{figure} \begin{center} \begin{tabular} {\vert c p{1.35in}\vert c p{1.35in... ...ex{Bidirectional data flow} & & \ \hline \end{tabular}\end{center}\end{figure}$

**Figure 6.8:** *Permitted data and event flow diagram connections.*
$\begin{figure} \begin{center} \includegraphics {p/DEFconnections.eps}\end{center}\end{figure}$

6.2.2 Constraint Checking

TDEFD checks all the constraints of TDFD. For these constraints see figure 6.6. The other constraints that TDEFD checks are listed in figure 6.9.

**Figure 6.9:** *Immediately checked and soft constraints on DEFDs (not part of TDFD).*
$\begin{figure} \begin{center} \includegraphics {p/DEFconstraints.eps}\end{center}\end{figure}$