TIME-CONSTRAINS PROJECT SCHEDULING PROBLEM WITH ACTIVITIES ALTERNATIVES, ANT COLONY OPTIMIZATION APPROACH

In this paper we handle the problem of scheduling/rescheduling project activities when there is more than one method (alternatives) available to execute the project activities, each method has its own time duration and resource requirements and also there is a dependency between the methods of execution the activities , A suggested method is presented here to deal with activities dependency and the ant colony optimization metaheuristic approach is used to find the best set of alternatives for the project activities in order to finish the project as soon as possible and identifying the critical path of the project. Introduction Project scheduling/ rescheduling (called scheduling in brief) is one of the most important topics in management many scheduling techniques have been developed and are widely used for projects like construction, research, maintenances,. ,etc. Bar chart is one of the simplest scheduling techniques but it does not clearly show the dependency among activities specially when there is more than one method of executing the activities (i.e. alternatives) the critical path method (CPM) is also a popular scheduling technique and used in project scheduling when the duration of activities is well known, when there is uncertainty around activities duration or there is a probabilistic nature of activities duration the Project Evaluation and Review Technique (pert) is used. A good start for the project management (or project scheduling problem) found in Rao [1] and a representation of the problem as a linear programming problem found in Phillips [2], recent directions and development of this topics found in Shih [3] Varizi [4] and Kolisch [6]. In general project scheduling is concerned with planning of activities over time subject to various constraints with the intension to reduce certain objective (cost or time), the main models for project scheduling are Kolisch [6]: A. Time constrained project scheduling problem (TCPSP) in this model the objective is to reduce the time duration of the project (also called makes span), we make use of this models to answer questions like what is the earliest time to finish the project and if uncertainty take place in the project we use this models to find the probability of finishing the project at or before a given deadline. B. Resource constrained project scheduling problem (RCPSP) these models concentrate on resource like budget, machines, workers,. , etc and try to reduce the cost to the minimum. C. Time cost trade off models these models build to minimize both project duration and the over all cost. D. Resource leveling models also known as resource leveling problem (RLP) these models search for the optimum usage of available resources and take into consideration variables like hire and fire of workers, available work space, how many project are executing at the same time and their priorities.etc. Problem definition In planning phase for any project the planner (or scheduler) will always face the problem of alternatives, these alternatives may be found for the same activity when there is more than one method to execute the activity, and also found among project activities i.e. the executing of