Dependencies Control Task Sequence

The simplest definition of a predecessor task is "a task that has to complete before an other task can begin" the "other" task in this task pair is, by definition, a successor task. Obviously, first we design the house, then we build it. The task of building the house "depends" on the task of designing it, because designing the house must precede building the house. When a predecessor/successor relationship like this exists between two tasks, we say that a dependency exists between the two tasks. It is very common for several tasks to occur one right after the other, in a series or chain of dependencies. Task A (Design House) can connect to Task B (Build House), which can connect to Task C (Paint House), which can connect to Task D (Sell House), and so forth. In this example, Task B is not only a successor to Task A, but is also a predecessor to Task C. Tasks can have several predecessors, and several successors.

Dependencies are not created automatically -- you must manually connect the tasks. One way to connect two tasks is with the link tool: click on the link tool button (the button that looks like two links of a chain) on the spreadsheet side (any column), click on the predecessor task, but do not release the mouse button until after you've moved the mouse cursor (link tool) to the successor task; or, connect the two tasks by using the select tool instead of the link tool: select the select tool by clicking on the button that looks like a Swiss cross on the spreadsheet side, select the predecessor task hold down the <Ctrl> key and click on the successor task press the <Ctrl-C> key combination. (If the selected task pair is already connected, you will be presented with a dialog box that asks if and how you want to modify the existing connection.)

Connect a series of tasks together at once: select the entire series of tasks by clicking on the first task in the series and dragging the mouse cursor to the last task in the series before releasing the mouse button press <Ctrl-C>.

You can easily turn on or off the display of dependency lines between tasks by clicking on the button that looks like two task bars with a line connecting them .

When the two tasks Build House and Paint House are first connected, it is assumed that the process of painting the house cannot start until the building process has ended. We call this kind of relationship an 'End-to-Start' relationship. However, we can assign a lead or lag time to the dependency relationship, and/or set the connection to the start of the predecessor, set the connection to the end of the successor. These kinds of dependencies are what we call non-standard dependencies. (FYI, in our high-end product Time Line for DOS, we call them partial dependencies.)

For instance, let's say that the process of painting the house can really start 2 months after the start of building the house. Quite simply, this would be a Start-to-Start relationship, with a lag of 2 months. Another instance of a non-standard dependency relationship could be one that exists between two tasks like "Order Parts" and "Receive Parts", if it takes a few days to get the parts after ordering them. To create or edit a non-standard dependency, bring up the Edit Dependency form. The first time you connect two tasks, a standard dependency is created (End-to-Start, no lead or lag) subsequent attempts to connect two tasks (that are already connected) will bring up a form that allows you to customize the connection.

Just as we caution you about entering Start or End dates into summary tasks, you should think about whether or not you want to set dependencies to summary tasks. When users trace dependency chains (especially critical paths), it is often easier to follow dependencies set to specific detail tasks instead of to summary tasks. Sometimes it does make more sense to set a dependency to a summary task, but if you have a choice between connecting to a detail or its summary, try to connect to the detail.

We have seen some inexperienced customers confuse the subject of dependencies with the subject of outline structure, possibly just because detail tasks are visually and functionally inseparable from their summary tasks. It is true that summary always occurs during, and only during the same period of time that its details occur; but this behavior is built into the software, and it has nothing whatsoever to do with dependency relationships. In fact, since summaries ALWAYS span the dates spanned by its details, the software will not even allow dependencies to exist between detail tasks and their summaries. (Likewise, the software will not allow you to indent a task beneath a task that is connected to.)