Planning and scheduling go hand in hand. In this section we will analytically compare the two major paradigms of interest such as, planning and scheduling. The main purpose of this comparative study is first to establish the clear-cut distinction between planning and scheduling paradigms. After that we will analyse how these two paradigms are complementary to each other. During this part we are mainly interested in looking at the theoretical aspects of these two domains.
A plan is the theory or the details of how something like a project will get done. A plan is used to create a road map for the achievement of an objective. A schedule, when linked to a plan, is assigning times and dates to specific steps of the plan. Planning is the process of identifying all activities necessary to complete the project while scheduling is the process of determining the sequential order of activities, assigning planned duration and determining the start and finish dates of each activity. Planning is a prerequisite to scheduling because there is no way to determine the sequence until they are defined…however they become synonymous because they are performed interactively.
A plan requires an outcome and is the road map for getting from the current moment to the future goal. Plans can be short term or long term. They always involve details and specific steps that guide the plan from start to finish. Plans should always make room for unforeseen events; for example if one part of the plan is contingent on an external factor, the plan should account for such an event.
Above figure depicts the planning task in its purest form in which planning takes the input from the external world based on some requirements or criteria and generates the sequence of actions so that the need from the external world is satisfied. In the figure the demands can either come from the marketing department describing the need of the market or directly from the customer, demanding the feasible plan that will fulfil the requirements of particular scenario. The main objective is to transfer these demands into rough plan to meet the demands. Then during the actual planning task the flow or sequence of actions is specified, which if carried out the demand in hand can be satisfied. Speaking more formally, it describes the transition from the initial state of the world to the goal state where demands are fulfilled.
It was still the time when most of the researchers were treating the problems from the planning and scheduling domains as a solely planning problem and the scheduling task was mainly considered as a sub-domain of planning. The real-life problems needed to achieve the optimal solution over some criteria such as, minimization of cost etc. Although, the pure planning techniques were quite successful for dealing with the long-term time horizon but for the short-term time they have limited applicability.
Even today there is a conceptualization about the scheduling task that it is a special case of planning in which the actions are already chosen and leaving only the question of allocating these orders for their assignment. This is an unfortunate trivialization of the scheduling task. As opposed to the planning task the scheduling has found its well-defined boundary line for its definition. The scheduling task can be defined from the various viewpoints such as, operations research, artificial intelligence etc. So before going on talking more about the scheduling let’s consider some of the few definitions that are widely accepted to describe the nature of scheduling task.
“Scheduling is the problem of assigning limited resources to tasks over time in order to optimize one or more objectives”
“Scheduling deals with the exact allocation of jobs over time, i.e., finding a resources that will process the job and time of processing”
“Scheduling deals with the temporal assignment of jobs to the limited resources where a set of constraints has to be regarded”
“Scheduling selects among the alternative plans and assigns resources and times for each job so that the assignment obey the temporal restrictions of jobs and the capacity limitations of a set of shared resources”
Scheduling is the process of determining times and dates to achieve specific objectives.Schedules, like plans, can be long term or short term. Often, short-term schedules are very important and linked to long-term schedules. When working with an organizational or institutional schedule, it is important that the different players working on a project coordinate their schedules and have access to one another’s schedules to ensure a smooth work flow.
As we have seen from above figure that planning often gets influenced by the external environmental factors and produces the partial order of task. These partial order of tasks serves as an input for the scheduling task. It can be seen from the same figure that the planning task is mainly concern with the question of “what should I do?” whereas scheduling mainly deals with the question of “how should I do it?” The following figure depicts the scheduling task in its purest form.
Despite the fact that planning and scheduling tasks have their separate existence as a research philosophy, they can be inter-linked with each other and thus forming the cohesive working environment. Such a type of environment is usually referred to as an integrated planning and scheduling environment. The following diagram depicts the integrated planning and scheduling environment.
Project Management Office Scheduling is an essential part of Project Management and that needs a lot of monitoring and cross referencing. The whole project depends on the schedule and hence reviewing it makes it fool-proof and hence it ensures the streamlined flow of activities leading to the completion of the project
|The planning task mainly deals with WHATactions need to be carried out in order to achieve the final goal-state of the Project.||The scheduling task mainly deals withfinding out WHEN/HOW to carry out the actions to optimize the criteria of the Project.|
|It mainly concerns with reasoning theconsequences of acting in order to choose among the set of possible courses of actions. E.g. A plan must consider a possible set of actions available and look for their consequences and choose one action that satisfies most of the requirements.||It is mainly concern with mapping of thevarious sets of tasks to the available resources for the specific time interval while satisfying the constraints.
E.g. Assign task A to machine A and task B to machine B. The duration of task A is x min. and that of task B is y min. etc.
|Input to the planning task:
1. A set of possible courses of actions.
2. A predictive model for underlying dynamics.
3. A performance measures for evaluating courses of action.
Output to the planning task:
One or more courses of actions that satisfy the specified set of requirements for performance. E.g. a travelling salesman problem.
a) A set of possible courses of action is a set of travel options: air-flights, car, railway etc.
b) Dynamics: say the travel dynamics, i.e., information regarding travel time, cost and the way travel time and cost affectseach other. How externalworldconditions affect such actions. For example, weather conditions etc.
c) A set of requirements specified by the external world. E.g. in city A on Monday, and Tuesday, in city B from Wednesday afternoon till Friday night. And in this case constraints on solution would be start no earlier than Sunday arrive before Saturday night etc., maximum expenditure should not exceed £1000.
|Input to the scheduling task:
1. A set of tasks to be assigned.
2. A set of available resources for the execution of task.
3. The capacity of the available resources.
4. The time intervals of the specified task.
5. The constraints imposed on the task.
Output to the scheduling task:
The output to the scheduling task is a schedule that assigns the given set of taskson the available resources by maintainingtheir time intervals without violating the constraints.
E.g. In job-shop scheduling set of inputs would be set of jobs such as drilling, milling etc. and available resources would be machines on which these jobs can be executed. The constraints can take the nature of no resource is assigned more than one job at a time, each job is completed before he starting of the next job (precedence relation among jobs) etc.
|PlanningcanbestatedasSatisfying(find somesolutionssatisfying theconstraints)or finding thefeasiblesetofsolutions transferringtheinitial stateoftheworld into thegoalstate.||Theschedulingtaskisnormallyseenasaoptimisation task over one or more objectivefunctionssuchasminimisationof thecostormaximisation oftheresource utilisationetc.|