Organizational Charts or Tree Diagrams
The NETDRAW procedure automatically draws any acyclic network.
They do not have to be representations of a project.
You can also use the procedure to draw
a general directed graph that has cycles,
if node location is specified or if the BREAKCYCLE option is specified.
The procedure attempts to draw the network in
a compact fashion, which may not always produce the expected result.
Trees form one such class of directed graphs that have an
inherent natural layout that may not be produced by the default
layout of PROC NETDRAW. The TREE option in the ACTNET statement
exploits the tree structure of the network
by laying the nodes out in the form of a tree.
A directed graph
is said to be a tree if it has a root and there is a unique directed
path from the root to every node in the tree. An equivalent
characterization of a tree is that the root node has no
predecessors and every other node has exactly one predecessor
(Even 1979).
Typical examples of trees that arise in project
management are organizational charts
or work breakdown structures. If the TREE option is specified,
the NETDRAW procedure checks if the network has a tree structure and
draws the network with the root at the left edge of the
diagram and the children of each node appearing to the right of the
node. In other words, the tree is drawn from left to right.
The NETDRAW procedure enables you to specify multiple trees in the
same Network data set;
each tree is drawn separately in the same
diagram with all the roots appearing at the left edge of the
diagram. Thus, you can use the TREE option as long as every node
in the network has at most one predecessor. It you specify the
TREE option and some node has multiple predecessors, the TREE option
is ignored and the procedure uses the default node-layout
algorithm.
There are several features that control the
appearance of the tree:
- The children of each node are placed in the order of occurrence
in the Network data set.
The (_X_,_Y_) coordinates of
each node are required to be integers. The procedure attempts
to place each node at the center of all its children, subject to the
requirement that the coordinates must be integers. This requirement
may cause some of the nodes to be positioned slightly off-center.
See Example 5.15.
- The SEPARATESONS option separates the children of a node,
if necessary, to
enable the parent node to be exactly centered with respect to its
children. See the second part of Example 5.15.
- The CENTERSUBTREE option can be used to center each node
with respect to the entire subtree originating from the node
instead of centering it with respect to its children.
- In graphics mode, you can change the
orientation of the network to be from top to bottom instead
of from left to right. To do so, use the ROTATETEXT option
in the ACTNET statement to rotate the text within the
nodes and the ROTATE global graphics option to rotate the
entire diagram by 90 degrees. See Example 5.18
for an illustration of this feature.
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
