Hello, everyone. We will be talking in our module about activity on arrow, which is also called the arrow diagram method or the RIJ method. And the reason why they refer to it as the IJ method is because activities in this specific scheduling tool or method. They are defined by referring to each construction activity from it's starting what we call node, let's say i to that ending node of that construction activity which is let's say j. So that's why sometimes they call it as the IJ scheduling method or the arrow diagram or what I refer to in the module here and what we will talk about it in our course activity on arrow or AOA. So what's an activity on arrow? Activity on arrow is also a scheduling tool that we going to learn in this module that highlighting the construction activities by arrows. So we represent them simply by arrows. And there is also, similar to the IJ method that I mentioned, this is the node we are talking about. So you have one node, an i and then a arrow, j, and activity name usually comes on top of that arrow. Moreover, events are, or these nodes represent an events in time, and the event in time for each node in the diagram you have is a starting or an ending point to one activity or to several activities. And we will go through couple of examples along this module to learn it and built it together in the following slides. As we mentioned in a previous modules, we learned how to draw a diagram, a network diagram, using an activity or node. Now before, actually, we started with activity on node diagram I give you couple of recommendations how to draw it. So lets go through the same thing. Some recommendations on how to build an activity on arrow or AOA. One, draw the arrows from the left to the right while you are moving to building your network. So for example you have activity i here, you draw the arrow, as you can see in the interactive diagram. You put the activity name, pouring concrete, assembling framework, erecting steel, and so on. And you end up that arrow with another node, let's say j. Moreover, j which is the ending node of the activity on the activity on arrow diagram has to be greater than i, the starting node on that arrow or that activity. So if i here equal two, j has to be anything larger than two. Two to three or four to five or maybe seven to ten or so on. And we will go also through an example later. Each construction activity must have a unique i and j number. You can't have an activity of concrete pouring and activity of assembling or the form work with the same starting node and the same finish node. Because as I told you in the beginning, in the introduction, that the IJ method refers to the activity, where it starts, where it finishes. So, to have the same start and finish in the same time it's okay but when we refer to the activity we refer to it as the IJ activity. So that's why it has to have a unique number. Moreover, always number the nodes after you develop your diagram and after you make sure the diagram is completed. Through the exercises we will go through you will notice that similar to the activity on nodes, the activity on arrows, you will not get it from the first time. Sometimes you're going to draw it and then you start delete a couple of activities, put them in the other sides, make sure that they are starting the relationships between all activities and so on. So after you finish all that and you have the diagram completed and the nodes are showing, then you start numbering these nodes in the diagram to finalize the last step in this scheduling tool. Minimize any crossovers whenever possible. If you remember, we also talked about that specific point in activity or node before it. So we gave this kind of example, if you have two arrows and each arrow here in activity on arrow diagram represent an activity. In activity or node the arrow represents the relationship. So if there is a crossover you can do either the curve like this here or the shape here just to highlight that this is a crossover that specific arrow. Do your best after you build your diagram, if you have a lot of crossovers, think about a way maybe to move things around to minimized these crossovers. Is a very good recommendation here. It is link to this one is the last one here, which is avoid any illogical loops. After you finish the diagram, also you might look at couple arrows will look like is exact or a lot of curves in the arrow, that's not a good recommendation. That's not a good habit when drawing an activity on arrow, even in activity on node. So try to avoid it as much as possible, and after you finish the diagram you might then redo it as a good habit to also think how to minimize both an illogical loops and the crossovers. Now one good points that I want to highlight in the recommendations for the activity on arrow is what we call the use of dummy activities whenever it's needed. And here I'm going to pause quickly and define what is a dummy activity. It is as following, dummy activity is indicated by a dashed line arrow and the dummy activity requires neither time nor resources but is needed to properly show the logic between two construction activities or more. So let's state an example here to highlight the use of the dummy activity. So if we have a node starting with i and we have activity x and at the end of it is j, node j. So if we say, for example, we have another activity, y, and it will go like this starting from i and finishes also in j, the activity on arrow or the IJ method. This will not satisfy the requirement for it because when we refer to specific activity we refer to the IJ number. Activity x, the IJ number, would be if we assume i is one, j is two. Set then the IJ number for activity x is one, two. But for activity y it does say here that we have the same IJ number which is a big, it's fundamental mistake to have it in activity on arrow, to have the same IJ number for both activities. So this is a wrong practice and you do not do it. To overcome this challenge you will then go to what we call the dummy activities. So let's say we have the first node i here and then we have activity x, the end note of activity x also will jump it to have j. But when we start representing activity y, we have another node going to it. In this case what we do here, what we did is activity x that ij numbers, or the ij for activity x, is definitely now different the ij for activity y. So let's say this is one two and activity y would be one three for k. So in order to meet this relationship where activity x and y meet to finishes at the same time, then we use what we call a dummy activity which I just highlighted in the definition. A dash lined arrow to satisfy or to show that properly the logic between these two activities. So this is just a simple example. This is along the practice, this is the right way to do it, and we will go through couple of examples now to be able to build on learning how to build an activity on arrow and move forward.