The third step of a typical Oracle | Primavera Risk (Pertmaster) Monte Carlo analysis is to validate the integrity of the schedule logic. The Primavera Risk schedule check flags areas of concern or note in the schedule. This training article will review the schedule check options that are set prior to running the report.
Video Walkthrough of the Oracle | Primavera Risk (Pertmaster) Schedule Check Options (Duration: 9 min: 58 sec)
Schedule Check Options: Checklist Tab
This section will review not only what the individual schedule checks that can be run but also why Primavera Risk checks for certain items that other scheduling tools do not. We will note areas where the schedule check overlaps with those in other tools and areas where Pertmaster sees things slightly differently due to the risk analysis focus. It is important to keep in mind that a flag does not mean the area of the schedule is bad or must be fixed, it is flagging a condition that could be a concern.
There is no schedule check in the world that can detect if a schedule is “good,” however they can find fundamental flaws in the logic that would indicate that the schedule is not clean. It is a good rule of thumb that if you choose not to clean a flaw, then you should document somewhere why the flaw is acceptable. A poor schedule invalidates a schedule Monte Carlo analysis. It is better to show and explain flaws than to have an analysis ruled as wrong. We will break these flags down by our view of order of importance relative to running an accurate schedule Monte Carlo analysis. Keep in mind that a check marked as low could potentially have more impact than a high impact flag in some cases.
Open the schedule check options by following the menu path Reports | Schedule Check Options…
- Critical Schedule Check Flags:
- Constraints – Hard constraints such as must-finish-on constraints, are generally seen as the most damaging constraint. Hard constraints should be looked at very hard and documented if they are truly correct. A hard constraint is basically taking the place of logic so if an activity has a hard constraint and predecessors, then the scheduler should determine if the task is logically or constraint driven. Soft constraints can be equally damaging in a schedule Monte Carlo analysis. Soft constraints should be used, however it is important that they are used properly. Often constraints and lags are interchanged which is a critical problem in many schedules. A lag will has a static duration that will not change as durations in the schedule change, however a constraint is generally used to hold float in the appropriate place. One constraint in the wrong place can completely destroy the validity of a the Monte Carlo analysis.
- Out of Sequence Logic (“broken logic”) – Out of sequence logic is technically wrong. Based on the progress override or retained logic setting, the analysis will still run, however activity splits and other unexpected issues may occur during the analysis. Although Pertmastercan technically handle out of sequence logic, by definition it is incorrect logic and casts doubt on the validity of the analysis. If a scheduler cannot follow a logic chain, then it might be concluded that they are less equipped to deal with a logic chain that now has uncertainty and risk events entered into the equation. Often schedulers status items out of order due to time issues. It is more time consuming to break the logic than to status items out of order. It is a shortcut used when workloads become too heavy. That being said, breaking the logic and correctly statusing a project should be the desired method, especially before running a schedule Monte Carlo analysis on the logic.
- Open Ended Task (Lacking Predecessor, Successor) – Pertmaster views open-ended tasks differently, and more correctly, than Primavera P6 and some other scheduling tools. A true open end is an item that does not have a predecessor connected to the activity start or a successor connected after the activity finish. Many scheduling tools look for a predecessor or successor relationship. For example, if an activity has a start-start predecessor and a start-start successor only, then there is nothing connected to the end of the task. PrimaveraP6 does not see this as open-ended, however Primavera Risk disagrees. The task has float to the end of the schedule and because there is no link from the finish of the activity. If the item has 90 days of float, then connecting an important 60 day risk to this task would show no schedule slip on the completion milestone. This issue can be seen by looking at the float calculations in any scheduling tool, however it is unfortunate that some scheduling tools do not check for open-ends in the same fashion. One open-ended task in a vital location can compromise the results of the Monte Carlo analysis. Although scheduling theory says that there should only be two open-ends, at the beginning and end, it is preferable not to link everything to the end of the project to avoid a schedule check flag. The logic becomes very hard to trace and the scheduler looks sloppy. If the activity truly cannot be a driver, then it would be preferable to discuss a path forward internally, however documenting these open-ends can often save a headache during an audit. Whether you link the activities or not, they should always be documented that they are in the schedule but cannot under any circumstance be a driving activity.
- Start to Finish Links – Start-finish links can be seen as backwards logic. There may be cases where the start-finish links were used intentionally, however it is normally done by accident. The start-finish link will accomplish basically the same logic as a finish-start link with an as late as possible constraint, so it could be used intentionally, however it is generally a flag that incorrect logic was put in the schedule by accident or the impact of the link type was misunderstood by the scheduler.
- Lags Longer than (x) Planning Units – Lags are quite simply an absence of logic. A one day absence of logic can do very little damage. A 30 day lag can do much more damage. It is important to realize what the lag is being used for. Is the lag being used because the schedule has float? The scheduler should use a constraint to hold float instead of a lag. Does the lag represent something that will happen but is not actually an activity like concrete curing time? Having a hard coded lag time might be a reasonable option. Does the lag represent many activities that should probably be loaded with risk? Sometimes the lag should be converted to an activity. Lags are like boxers, the bigger ones look much scarier. Long lags are one reason that Monte Carlo analysis on a summary schedule becomes challenging. Large lags and great quantities of representative logic exist in many summary schedules.
Lower Risk Flags:
- Negative Lags (“leads”) – Negative lags are often seen as the bad word of scheduling environments. Pertmaster handles negative lags logically correctly. Whether negative lags are allowed in your company or not, it is important that the negative lags are converted properly. The most common method is to create a start-start link with a positive lag. If the finish of the predecessor activity is the driver, then the start-start link is wrong. The planner should either be using a small negative lag or breaking the activity into multiple parts. In the start-start link scenario, if the predecessor activity increases in duration, then it would not push out the successor because they are tied with a start-start relationship. An incorrect start-start relationship is much worse than a negative lag. Large negative lags are definitely a red flag just like large positive lags. It is always important to ask the question if an activity is being driven by the start or finish of the predecessor. If the activity is being driven by the finish of an activity, then using a start-start link is unacceptable.
- Positive Lags on Finish to Start Links – Pertmaster flags all lags so that the user can verify them.
- Links to or from Summary Tasks – Microsoft Project allows users to create links to and from summary tasks. This is not generally considered good form. It can work if the scheduler did this on purpose, however generally it is a mistake.
- Lags Between Tasks with Different Calendars – Many commercial scheduling tools handle these links differently. A lag is usually put on the predecessor task, successor task, or a seven day calendar. It is important to realize how your scheduling tool handles lag calendars and make certain that the entered lag durations are in-line with the software. A seven day lag put on a five day calendar can cause up to eleven days of schedule impact without any other non-working periods. It is important that schedulers are inputting lag dates that are in-line with the calendar. An example situation would be a link between an engineering activity on a five day calendar and a construction activity on a six day calendar. The link may be on a five day calendar based on the engineering calendar, however the lag is entered at 6 days because the scheduler is thinking about the construction calendar. This is not a huge issue but can cause some problems.
- Duration Uncertainty Distribution Shape – The duration uncertainty shape has nothing to do with schedule logic. This check is used to find three-point estimates that are skewed to the maximum value. The more a risk range is skewed in a pessimistic manner, the more likely that a risk event exists in the activity and should be documented and put into the risk register. When the risk event is separated, the remaining risk range will probably change. This check is designed to help risk analysts separate uncertainty and productivity from discrete risk events.
Schedule Check Options: Rationale Tab
The schedule rationale tab gives the Oracle reasoning behind each check. Users can choose to have the rationale put in the report as documented or with user-defined edits.
Schedule Check Options: Options Tab
The options tab has a few check box and drop-down options for running the report. The options are related to how the data is displayed in the report and not which checks are run. The options can be edited based on user or company preferences, however the default settings can be used for most project managers.