|The GANTT Procedure|
The variables required by PROC GANTT to establish a valid AOA specification are defined using the HEADNODE= and TAILNODE= options in the CHART statement.
The variables required by PROC GANTT to establish a valid AON specification are defined by the ACTIVITY= and SUCCESSOR= options in the CHART statement. Optionally, nonstandard precedence relationships can be specified using the LAG= option in the CHART statement to define a variable that defines the lag type of a relationship.
Every connection is comprised of either three or five segments and is termed a 3-segment or a 5-segment connection, respectively. The segments are routed in the following sequence:
Every connection begins with a horizontal line segment originating from the activity's logic bar and ends with a a horizontal line segment terminating at the successor's logic bar. If the lag type of the relationship is SS or SF, the initial horizontal segment originates from the left end of the activity's logic bar, else it originates from the right end of the logic bar. If the lag type of the relationship is SS or FS, the final horizontal segment terminates at the left end of the successor's logic bar, else it terminates at the right end of the logic bar.
Note: The ends of the bars must be consistent with the lag type of the connection if it is to be drawn; that is, the left end of the activity's logic bar must represent a start time if an SS or SF lag type connection is to be drawn, and the right end of the activity's logic bar must represent a finish time if an FS or FF lag type connection is to be drawn.
Violation of these conditions is unlikely when using the Schedule data set generated by PROC CPM. An example violating these conditions is a Schedule data set containing incorrect or invalid data. The following example illustrates two observations that are in violation of these conditions. The first observation is invalid data ( E_START greater than E_FINISH) while the second observation is incomplete (missing E_START and L_FINISH times).
E_START E_FINISH L_START L_FINISH 03MAR92 01MAR92 . . . 05MAR92 07MAR92 .
The following figure illustrates two typical precedence connections between an activity and its successor.
ACTIVITY SUCCESSOR LAG A C FS B C FS
The connection from activity
A to activity
C is comprised of three
segments PQ, QR, and RT whereas the connection from activity
B to activity
C is made up of five segments UV, VW, WX, XS, and ST; the two additional
segments correspond to the optional segments mentioned in item d) above.
Points Q, R, V, W, X, and S are turning points.
Note: The use of the term "global" is attributed to the fact that in any connection from an activity to its successor, the global vertical of the activity corresponds to the only segment that travels from activity to successor.
The following figure illustrates the two global verticals of activity
A has four successors: activities
The lag type of the relationship between
B is nonstandard, namely
'Start-to-Start', as is that between
D. The other two lag types are standard.
The start and finish global verticals of activity
A are represented by the two dotted lines.
The vertical segments of the SS lag type connections from
B and from
that are placed along the start global vertical of
A are labelled PQ and RS, respectively.
The vertical segments of the FS lag type connections from
C and from
that are placed along the finish global vertical of
A are labelled TU and UV, respectively.
For a given connection from activity to successor, the vertical segment that is placed on the activity global vertical is connected to the appropriate end of the logic bar by the horizontal segment described in item a) above. The minimum length of this horizontal segment is specified with the MINOFFGV= option in the CHART statement. Further, the length of this segment is affected by the MININTGV= option in the CHART statement, which is the minimum interdistance of any two global verticals. In Figure 4.8, the horizontal segments QW and RX connect the vertical segments PQ and RS, respectively, to the logic bar and the horizontal segment YU connects both vertical segments TU and UV to the logic bar.
Figure 4.9 illustrates the positions of the horizontal
tracks for an activity in a Gantt chart with four schedule bars. Three of
the horizontal tracks, namely
track 4, and
service the start of the logic bar
and are connected to one another by a vertical track
referred to as the Start Local Vertical.
Similarly, the horizontal tracks
service the finish of the bar and are interconnected by a
vertical track referred to as the Finish Local Vertical.
The local verticals are used for
placement of the vertical segment described in item d) above.
Note: The use of the term "local" is attributed to the fact that
the local vertical is used to connect horizontal tracks
associated with the same activity.
track 1 and
track 7 terminate upon their intersection with the
start local vertical and that
track 2 and
terminate upon their intersection with the finish local vertical.
The minimum distance of a local vertical from its respective
bar end is specified with the MINOFFLV= option in the CHART statement.
The maximum displacement of the local vertical from this point
is specified using the MAXDISLV= option in the CHART statement.
The MAXDISLV= option is used to offset the local vertical in order
to prevent overlap with any global verticals.
Arrowheads are drawn by default on the horizontal tracks corresponding to the
logic bar, namely
track 4, and
upon entering the bar and on continuing pages. The NOARROWHEAD
option is used to suppress the display of arrowheads.
The routing of a SS or FS type precedence connection from activity to successor is described below. A similar discussion holds for the routing of a SF or FF type precedence connection.
Suppose the activity lies above the successor. Let the start local vertical of the successor be denoted by slv, and let the appropriate global vertical of the activity be denoted by gv.
If gv lies to the left of slv,
then the connection is routed vertically down along gv onto
track 4 of the
successor, on which it is routed horizontally to enter the bar. The
resulting 3-segment connection is shown in Figure 4.10.
An example of this type of routing is illustrated by the connection between activities
C in Figure 4.7.
If gv lies to the right of slv, then the connection is routed
vertically down along gv onto
track 1 of the successor, horizontally to the left
to meet slv, vertically down along slv onto
track 4 of the successor
and horizontally to the right to enter the bar.
The resulting 5-segment connection is shown in Figure 4.11.
This type of routing is illustrated by the connection between activities
C in Figure 4.7.
An identical description applies when the activity lies below the
successor, with the only difference being that
track 7 is used in place of
track 1 (see Figure 4.9).
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.