NASA's Experiment Scheduling Program (ESP), which has been used for approximately 12 Spacelab missions, is being enhanced with the addition of a Graphical Timeline Editor. The GTE Clipboard, as it is called, was developed to demonstrate new technology which will lead the development of International Space Station Alpha's Payload Planning System and support the remaining Spacelab missions. ESP's GTE Clipboard is developed in C using MIT's X Windows System X11R5 and follows OSF/Motif Style Guide Revision 1.2

Jaap, John P.

Meyer, Patrick E.

English

NASA Technical Reports Server

Graphical Timeline Editing
N95- 23746
Patrick E. Meyer and John P. Jaap
National Aeronautics and Space Administration (NASA)
Marshall Space Flight Center, AL 35812
Phone (205) 544-2265 Fax (205) 544-5873
Email: Patrick.Meyer@msfc.nasa.gov
KEY WORDS AND PHRASES
Conflict resolution, graphical editing, re-
scheduling, scheduling, space station.
INTRODUCTION
NASA's Experiment Scheduling Program
(ESP), which has been used for approximately
12 Spacelab missions, is being enhanced with
the addition of a Graphical Timeline Editor.
The GTE Clipboard, as it is called, was devel-
oped to demonstrate new technology which will
lead the development of International Space
Station Alpha's Payload Planning System and
support the remaining Spacelab missions.
ESP's GTE Clipboard is developed in C us-
ing MIT's X Windows System TM X11R5 and
follows OSF/Motif TM Style Guide Revision 1.2.
Clipboard Concept
In ESP's GTE Clipboard concept, what is in
the clipboard is not in the timeline. This re-
duces the permutations of potential conflict and
allows for capabilities that would otherwise be
too cumbersome or impossible. Activities to be
edited must be moved to the clipboard, edited
within the clipboard, and committed back to the
timeline. When desired, a subset of the edited
activities in the clipboard can be committed to
the timeline. Activities from external sources
can be added to the clipboard where possible
conflicts can be resolved before they are moved
to the timeline.
EDITING
"Editing," the key word in Graphical Time-
line Editing, is a combination of rendering the
timeline as graphics objects and supporting user
manipulation of those objects. When rendering
the data, pixel granularity inherent in graphic
editors is overcome by using a "high resolu-
tion" screen. However, when manipulating
data, the pixel granularity problem is exacer-
bated in the clipboard because ESP can have a
scheduling horizon of 90 days or more and si-
multaneously maintain time accuracies to 1 sec-
ond - a ratio of 1 to 10 million. In addition,
users of ESP frequently need to maintain sched-
uling granularity at 1 minute. An eloquent so-
lution to both problems was found and
implemented.
The clipboard provides two methods for ad-
dressing time granularity problems. First, time
quantization is used to round modified times to
the nearest multiple of a user-specified con-
stant. During an activity modification, feed-
back provides the quantized placement times so
the user is constantly aware of the modified
value. Second, a mechanism which allows the
user to make micro-adjustments is provided.
Micro-adjustments are always made in a
quantization unit even when the unit is smaller
than a pixel.
With a solution to the granularity problem
in hand, fundamental graphical editing features
such as selecting, adding, deleting, moving,
modifying, undoing, aligning, and commiting
back to the timeline can be straightforwardly
implemented.
Activity Selection
For the clipboard, three methods and two
modes of selection were identified. The meth-
ods include selecting the lowest integral part of
a scheduled activity (a step), selecting a whole
activity (a performance), and selecting all steps
within a user-bounded box. For each of these
methods, the modes of selection are additive
(extending) and toggle.
Selection order may be relevant for some
manipulations. For instance, to temporally
align, both the activity which is aligned to and
the activity which is aligned with must be speci-
fied. By using selection order, the alignment
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https://ntrs.nasa.gov/search.jsp?R=19950017326 2020-06-16T08:33:02+00:00Z
can be made consecutively; i.e. a successor can
align with its predecessor.
Selected activities are rendered with angled
appendages because it provides optimum view-
ability for overlapping and/or extremely small
steps. Figure 1 below illustrates the usability of
this method. Steps 1, 2, and 4 are shown as se-
lected.
Figure 1 Selected Activity
Adding Activities
Activities can be added to the clipboard by
moving them from the current timeline to the
clipboard, copying from the current timeline,
importing from an external timeline, including
a template of a model, using the automatic
scheduler, and keying in data.
Each of these methods has unique applica-
tions and advantages. Activities which could
not be imported directly to the timeline may be
imported to the clipboard, repaired, and then
moved to the timeline. Adding a template of a
model to the clipboard allows a user to start
with a generic form of model and massage it to
fit the timeline constraints. Adding to the clip-
board via automatic scheduling provides
conflict-free activities in the clipboard to which
the user can make minor adjustments before
moving them to the timeline. However, auto-
scheduling into the clipboard checks constraints
only against the timeline and not against the
clipboard.
Deleting Activities
Activities may be deleted from the clip-
board. After deletion they may be restored un-
til they are purged or until the entire contents of
the clipboard is successfully committed to the
timeline. As a shortcut, activities may also be
deleted directly from the timeline.
Moving Clipboard Activities
Moving activities is the most used manipu-
lation of a timeline and therefore should be ro-
bust and easy to use. In the clipboard, moving
selected steps is initiated with a mouse button
press while the pointer is within one of the se-
lected steps. The initiating step's new start
time is fed back to the user during the modifica-
tion to indicate where the step will be placed.
Other selected steps are also moved.
Modifying Activities
After moving or adding activities, small
conflicts usually arise that require simple modi-
fications for them to validly schedule as a
group. For example, activity duration changes
will routinely introduce overlap conflicts. By
proper definition of activity duration changes,
the user can prevent overlap conflicts. The
definition chosen for the clipboard takes all
succeeding (for modified start time) or all pre-
ceding (for modified end time) activities which
are selected and shifts them to maintain the
original time delay between the changed activ-
ity and any other affected activity. In Figure 2
below, the duration of B was changed causing
C to be shifted.
Before:
mx-"l I B
After:
r---r-q
Figure 2 Duration Change
However, when changing the duration of an
activity, the durations of overlapping selected
steps are also modifed rather than being shifted.
This overlap may or may not be due to schedul-
ing concurrency constraints (see Figure 3 be-
low).
Before:
I B I
After:
I A I
I 8 I
Figure 3 Overlapping Change
Modifying Crew Usage
A portion of the display can be used to dis-
play crew usage data for both the timeline and
clipboard. Graphical manipulations within this
area can remove, add, or reassign crew on an
activity.
Undoing Modifications
Undo, as the name implies, allows the user
to undo the last edit made to the clipboard. The
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last edit may be either a simple (one item) or
compound (multiple items) edit. In addition,
undo can also restore activities to their unedited
state until they are committed to the timeline.
Assisted Temporal Aligning
The clipboard can align selected activity
steps or activity performances in four ways:
• Start time to start time.
• Start time to end time.
• End time to start time.
• End time to end time.
Steps are aligned consecutively in the order in
which they were selected.
Committing to the Timeline
As stated before, activities in the clipboard
are not in the timeline and must be committed
to the schedule. During committal to the time-
line, activities are validated and any conflicts
that the user has not resolved are reported. If
no conflicts are present, the activities are
moved from the clipboard to the timeline with
no report.
USER INTERFACE
While building the basic editing commands
into a new timeline editor, concerns of leaving
behind old, but good, ways of editing arose.
Therefore, the clipboard brings forward text-
based editing features similar to ESP's previous
timeline editing buffers. These include a table
and command line which allow the user to enter
specific values for important aspects of an ac-
tivity and enter commands that can affect
ranges of activities.
Tailorable Displays
Each Spacelab mission ESP supports has
different objectives and resource utilization.
To accommodate the varying demands on the
clipboard, a tailorable display allows users to
hone in on the information which is important
to the type of missions they are scheduling.
Some of the options included are --
• Activity Breakdown --Using Digital's Struc-
tured Visual Navigation (SVN) widget the
clipboard is able to present the graphical
data to the user in an expandable outline
form. With SVN, the user can expand an ac-
tivity to a Gantt chart of its steps.
• Optional Command Line --For the expert
graphical editing user, the command line
may be removed from the visible display.
• Optional Crew Data --For missions where
activities are not crew-based, the crew time-
line data can be removed.
• Optional Crew Timeline Data --Since what
is in the clipboard is not in the timeline, the
crew timeline data can be displayed in the
same crew area with clipboard data.
• Paned Windows --The clipboard utilizes
Motif's PanedWindow widget which allows
the user to subdivide the display and view
the most desired information.
• Toolboxes --The clipboard toolbox provides
quick access to copy, delete, undo, auto-
schedule (generate), move (bias), temporally
align and other useful commands.
CONFLICT RESOLUTION/PREVENTION
The biggest drawback with many manual
editors is their "guess-again" approach. When
the user moves an activity, the scheduler re-
sponse is to report resource constraint and
scheduling conflicts and the user is forced to
"guess again" where the activity can be validly
placed to avoid the conflicts. The clipboard not
only provides a report when edits are commit-
ted, it also displays graphics information to help
the user eliminate existing conflicts and to
avoid introducing conflicts when activities axe
manipulated. When fully implemented, the
clipboard will also provide automatic schedul-
ing assistance.
Visual Aid for Crew Conflicts
Since ESP enforces the Spacelab and Inter-
national Space Station Alpha ground rule that a
crewmember cannot be scheduled to do more
than one task at a time, the clipboard provides
a crew timeline area where the crew timeline
data is displayed, the crew clipboard data is
overlayed, and any conflicts are highlighted.
Users can readily see where crewmembers are
available or are in conflict and can modify crew
usage for activities in the clipboard.
Visual Aid for Temporal Constraints
An activity can have temporal constraints
relative to other performances of the same
367
model or other models and can have fixed win-
dows in which it must be performed. While
other displays in ESP can show the data which
determines where the temporal constraints are
met, the clipboard can compute the feasibility
windows and present them to the user so that
temporal conficts can be avoided or removed.
The clipboard uses an X Windows "work
procedure" to compute and display these
computationally-intense windows. Work pro-
cedures are executed when no events are pend-
ing execution; i.e., they use idle computer time.
The clipboard re-launches the work procedure
whenever the timeline is changed; therefore, the
windows remain current.
Visual Aid for Resource Constraints
Each step of an activity can have many con-
straints which limit where on the timeline a step
can be validly placed. In addition to crew re-
quirements, these constraints include other
shared resources and windows of opportunity.
For each step, the clipboard can compare each
requirement to the current timeline state, con-
solidate all the individual results, and present
feasibility windows on a single line of the dis-
play. Windows which are not as long as the
minimum step duration are not shown. By ad-
hering to the feasibility windows, the user can
easily avoid introducing conflicts or remove ex-
isting conflicts. A work procedure is also used
for these feasibility windows. Figure 4 shows a
step which is too long for its nearest feasibility
window but which will fit within the next win-
dow.
Figure 4 Feasibility Windows
Users may request that feasibilities for a
step be presented on an individual requirements
basis. This separate display will show each re-
quirement of the selected step and the time peri-
ods when that requirement is met. The
composite feasibility windows are also shown.
Automatic Assistance to Editing
As an enhancement of the manual editing
process, the clipboard provides automatic as-
sistance. In this mode, the user selects a per-
formance that is in the clipboard but conflicts
with some constraints. The user specifies a ho-
rizon over which scheduling is to take place,
and an automatic scheduler adjusts step start
times, durations, and crew assignments to avoid
conflicts. An explanation facility which graphi-
cally explains what the scheduler did allows the
user to understand what conflicts were ad-
dressed or why a solution was not found.
A future enhancement of automatic re-
scheduling is to allow the user to specify an-
other horizon over which the program may
automatically adjust activities already on the
timeline. This process may proceed without
user interaction, or user approval may be re-
quired for every change to the timeline. There
are several strategies for directly modifying the
existing timeline:
• Reassignment of crew.
• Adjusting step durations or delays.
• Substituting an alternate scenario of the
same activity.
• Moving activities to non-conflicting times.
• Moving activities to new times where con-
flicts can be easily resolved.
• Deleting activities based on priorities or
based on least impact to schedule.
Advanced techniques such as simulated an-
nealing are also candidates for automatic assis-
tance.
SUMMARY
The X Windows Graphical Timeline Editor
currently being added to the Experiment Sched-
uling Program is based on a clipboard concept.
Because activities which are in the clipboard
are not on the timeline, robust capabilities
which may not have been otherwise practical
are being incorporated. The GTE Clipboard is
being implemented using Motif TM and other
widgets and includes a complete suite of
graphic manipulation features and a complete
suite of timeline editing features relative to
Spacelab and International Space Station Al-
pha. The GTE Clipboard is much more than a
"guess-again" editor in that it provides
graphical assistance for conflict resolution. Fu-
ture plans will implement automated conflict
resolution.
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