DITOPS is an advanced tool for generation, analysis and revision of crisis-action
logistics schedules. It was developed to address the shortcomings of existing
transportation scheduling tools: these tools typically provide rather inflexible
solution generators; the user is given no guidance in changing input constraints
to achieve desired results, and has no control over how the schedule actually
changes in response to revised inputs. As opposed to this, the DITOPS reactive
scheduler is a mixed initiative decision-support tool similar in spirit
to spreadsheet programs: sets of scheduling decisions and solution constraints
are interactively manipulated by the user at (typically aggregate) levels
consistent with user-task models. At each step, the system applies appropriate
(re)scheduling procedures to impose the changes specified by the user,
and provides localized consequences of each change. In other words, the
user sees "the big picture" and can operate in terms of understandable
and manageable real-world concepts, while the system "manages the details",
takes care of the multitude of small and uninteresting albeit important
scheduling decisions. System look-ahead analysis and scheduling techniques
further provide functionality that transcends the spreadsheet decision-support
analogy, supporting the user in identifying principal causes of observed
solution deficiencies (e.g., resource bottlenecks), in analyzing various
decision-making options (e.g., apportionment of additional resources),
and in assessing solution sensitivity to various executional circumstances.
The incremental nature of (re)scheduling in DITOPS makes it ideal for reactive
scheduling. The system is capable of repairing a schedule as a response
to unexpected events (such as resource breakdowns), minimizing disruption
to other parts of the schedule.
The mixed initiative "spreadsheet" model of operation also makes DITOPS well suited to "what if" -experimentation. It should be observed that scheduling is often much more than just placing activities on a time-line; it is a process of "getting the constraints right", e.g. trying to assess resource requirements ("how many ships do I need to complete the mission in time?"). Traditional simulation approaches are not suited to this type of problem solving (it would effectively require one to "run the simulation backwards"). DITOPS, however, is capable of relaxing constraints in several dimensions, not just temporal ones, allowing it to be used efficiently when scheduling is tightly coupled with planning. This is often a more natural approach than having to artificially decouple the planning and scheduling tasks just because existing tools don't allow their easy integration.
Principle of Operation
The DITOPS system incorporates concepts of constraint-directed scheduling
developed within the OPIS manufacturing scheduling system, together with
extensions to address the specific characteristics of transportation scheduling
problems. At the core of the system is an incremental, reactive framework
for generating and revising schedules, integrating three principal components:
The alternative scheduling procedures are specifically designed to provide differential optimization and conflict resolution capabilities. Local search methods exist for both "resource" and "movement" centered scheduling, respectively providing capabilities for manipulating (i.e., revising or extending) the schedules associated with particular sets of resources (e.g., a cargo ship fleet) or particular sets of temporally related movements (e.g., the movements associated with a particular force module). By virtue of search orientation, each of these methods emphasizes specific optimization biases; resource scheduling promotes efficient use of available transport capacity while attempting to minimize the tardiness of scheduled movements. Movement scheduling, alternatively, promotes enforcement of arrival constraints and efficient synchronization of dependent movements, while attempting to minimize asset capacity requirements. Both of these methods share a common search infra-structure that allows incorporation of additional allocation preferences. A number of more specialized revision procedures are also defined, providing additional capabilities to shift the scheduled interval of "trips", re-allocated batches associated with particular transportation assets, and do load balancing to exploit increases in port capacity.
DITOPS is built using an underlying scheduling framework called OZONE (aka
O3 aka Object-Oriented Opis). OZONE is implemented using object-oriented
representation and programming techniques, providing an extensible modeling
and scheduling framework that enables straightforward system customization
to account for the principal constraints and objectives of different scheduling
domains. The scheduler operates with respect to hierarchical models of
the processes and resources of the problem domain. Because of a layered
and extensible nature of the OZONE modeling and scheduling framework, new
application development is not limited to transportation problems: the
system can also be adapted to, say, manufacturing scheduling problems.
In practical terms the framework is a class library that contains classes
for the basic scheduling concepts and their specializations to some specific
areas (e.g. transportation). Protocols are provided for combining concepts
from the library, and extending the existing basic concepts into more specialized
Due to the configurability of DITOPS/OZONE it is easy to integrate it or parts of its functionality with other planning systems. In an early technology integration experiment (TIE) with SRI, DITOPS was used to perform resource capacity analysis for higher level course of action planning by integrating it with SRI's SOCAP planner running on the Common Prototyping Environment (CPE) developed by BBN. Some DITOPS functionality was also embedded into BBN's TARGET mission planning system to perform feasibility checking and conflict diagnosis of course of action plans. More recently the OZONE class library has been applied to develop a prototype system for aero-medical evacutation (re)planning.
The current version of DITOPS runs on a Sun Sparcstation. A more portable version, aimed additionally at PC and Mac platforms and utilizing a Java-based interface is nearing completion. Interaction with the user takes place through a direct-manipulation user-interface which is centered around Gantt-diagrams of resource capacity usage (see Figure 1). In comparison to conventionally used simulation approaches to producing schedules for large-scale deployment problems, we have demonstrated that DITOPS is able to efficiently generate higher quality schedules while simultaneously satisfying a wider range of deployment constraints. For example, DITOPS is currently capable of generating a detailed 3000-movement TPFDD (Time-Phased Force Deployment Data) schedule in about 6 minutes (on a Sparcstation 10).
Current efforts are extending and adapting the OZONE/DITOPS framework for application in two different scheduling domains: