Lots of relationships as I explained in construction industry, we usually have the first three are the most common used ones in our industry. Which is a finish-to-start relationship, start-to-start relationship, finish-to-finish relationship. As for these two is when the start of activity to finish of an activity relationship and the multiple relationships in our industry. I would suggest to try away from that and avoid it using them in your schedule. It's not that common, it's rare and almost always you can still present the relationship between any activities with the first three in your project. Finish to start relationships it is the most common type of relationship as I explained earlier. And as I mentioned several schedulers, several construction managers on their projects still prefer to only use this type of relationship between their construction activities. So for example, we cannot start assembling the windows, or even doors, until the window or door frame are installed. Let's go through a more detailed example with some numbers here. So as we can see here, from this example we cannot pull a concrete until the form work is done. So for example if we have a wall or a column or a footing forms. We will not start the second activity of a concrete, as we can see maybe at the end date of placing the forms of 30. And the start date or the start date of is also 50. So there is no even gap between both. However let's go through an example where we do have a gap, or what I call a lag. Which we expanded before in other module such as the following one. Now, what we see here after we put the concrete, we are waiting around 3 days, when we say 3 days, the minimum, they or the minimum number of waiting has to be 3. You can wait a little bit more, but not less than 3 before you start the other activities of taking out the forms. That's why if you notice, the early start of the following activity is 35, which is 32 plus 3 of 35. So now this is an example where we have no lag and this is an example where we have a lag. But I want to explain a little bit more that basically we can still present or represent this with three activities, not just two. So for example, we can say that we have, Pour of the concrete, and then here we have the, Take out the forms. And what we said is we have three days, As lag. This can also be presented as pouring concrete. And you have take out the form but you can add another activity referring to the cure of the concrete. To wait for the concrete until its hardened enough before you take out the form. And then, you can connect it with the relationships as we can see here. So, from that aspect, both are still okay, we can use them both but I do prefer, if my advice for you is to go with the first one which highlighting the lag. So, however using no this, so how I explain it to you we can redraw this with three activities. But if you noticed, I told you I prefer the lag because using lag can save a very good number of construction activities from being added to the president's diagram. For example, if you do have a building, a high rise building, a multi-story building, and we do have several pouring activities over concrete. So imagine how many activities of the word just the cure concrete. You can take it out and just represent it with an arrow with a number three or two on top of it to highlight the relationship of just waiting time. And not resources are being used. So, what I explain about the tradition of relationship is similar to this one here. If finish to start relationship with no lag or lag equals zero, that's the traditional relationship. Adding the lag, will no longer categorize the relationship as traditional, but still it use the finish to start type relationship. So any finish to start type relationship with lag equal one and more still this is not considered as traditional. As long as this is zero lag, then that's the traditional relationship what we refers to.
