Inspecting Task Resource Drivers with BPC Logic Filter for Microsoft Project

BPC Logic Filter – an add-in for Microsoft Project (desktop) – includes an advanced Logic Inspector feature to greatly simplify the examination and navigation of resource-leveled, logic-driven schedule activities.

The resource leveling feature in Microsoft Project (MSP) offers an effective method for management of resource-constrained projects, but most project managers don’t appreciate its impact on Total Slack, the Critical flag, and the resulting “critical path.”  Specifically, all of those terms become unreliable or misleading in the presence of resource leveling.  I first wrote about those issues here.

With some improvements to BPC Logic Filter – we were able to identify resource-driving links and include them in The Resource-Constrained Critical Path and in other logical path analyses.

Analyzing logical paths in schedules requires detailed examination of each task’s dependencies and (for leveled schedules) resource assignments. It’s helpful to have the results of such examinations at hand while reviewing (and confirming) the logical path analyses, so recent versions include a task Logic Inspector for Inspecting Task Links with BPC Logic Filter.

Logic Inspector also includes inferred resource-driving links if desired by the user.  Consider this simple resource-leveled schedule from the earlier articles.

With resource-checking disabled (and no calendars or constraints to confuse things), BPC Logic Filter computes relative float and identifies driving predecessors in a way that is consistent with MSP’s calculation of total slack.  For the A2 Structures task (ID 11), this means that the driving predecessor is the only predecessor — ID10: A2 Civil — even though it finishes two weeks before A2 Structures starts.  It also means that A2 Structures is logically driving all three of its successors.

While this method is useful for understanding how MSP computes slack in resource leveled schedules, it does not help in understanding the actual resource limitations that drive the schedule of a task.  To gain that understanding, we first visit the Tracing Preferences tab in the Settings and ensure that Resource Checking is enabled.

Now Logic Inspector shows us the true picture of the schedule of the A2 Structures task.  Namely:

1. A new predecessor — the true driving predecessor for the task — is identified: the A1 Structures task in Area 1 must finish (and release its resources) before the A2 Structures task can start.  The only explicit logical predecessor of the A2 Structures task — ID10: A2 Civil — has 10 days of relative float.  That is, it could slip two weeks according to the standard calendar before THIS RELATIONSHIP starts to drive the A2 Structures task.

2. A new “driven successor” is identified in that the A3 Structures task may not start until the structural resources are finished with A2 Structures.

3. The A2 Electrical Change Order 1 task is actually 40 days (8 weeks) away from being driven by its relationship to the current task.  (It is in fact driven by other resource constraints.)

The JUMP button — which allows on-the-fly exploration of the schedule through logic links — treats the (implicit) resource driving links the same as explicit logical relationships.  Consequently, it is just as easy to hop through the logic of most resource-leveled schedules as it is to hop through one with no resources at all.

Dangling Logic in Project Schedules

Logic Driven project schedules can suffer from two kinds of open-ended or Dangling Logic, which makes the resulting schedule unreliable for dates or float analysis.

Project schedules need robust logical bases to reach two primary objectives:

  1. A schedule that accurately represents a true and achievable plan for executing the work – including technological and resource constraints.
  2. A schedule that supports accurate forecasting of consequences when the work does not proceed as originally planned – for example when activities fail to start or finish on time.

Dangling Activities – CPM

Logic-driven scheduling – often generically identified as “Critical Path Method” (CPM) scheduling – determines schedule dates by enforcing stringent logical sequential relationships between tasks from the start to the finish of the project.  The definition of adequate scheduling logic depends on the details of the project.  Logic is clearly inadequate, however, if any activity in the schedule is left logically disconnected from either the project start or the project finish – i.e. the activity is left “dangling.”  In the simple network diagram shown below, four activities are shown with no predecessors, while one activity is shown with no successors.  These cases typically represent omission of legitimate logical relationships with other (latent predecessor/successor) activities.  As a consequence, the early and late dates – and the Total Float – of all potentially-connected activities are not reliable.  The objectives of the logic-driven schedule can’t be met.  As a general rule, every activity in any CPM schedule – except the start and finish milestones – must have at least one predecessor and at least one successor.  Dangling activities not meeting this rule – also known as open-ended activities – indicate inadequate schedule logic.

Dangling activities that are missing predecessors and/or successors are relatively easy to isolate in project scheduling tools – including Microsoft Project (MSP) and Oracle Primavera P6 (P6) – by using an activity filter that searches for empty “predecessors” or “successors” fields.  It is common for experienced schedulers to routinely tie such dangling activities to general-purpose milestones such as “notice to proceed” (as a predecessor) or “substantial completion” (as a successor).  Such an approach removes the obvious indication of inadequate logic.  Close review of the relationships at such “merge points” in the schedule may still be necessary to identify activities whose true predecessors and successors are not sufficiently defined.

Dangling Activities – PDM

Most modern scheduling software implements a variation of CPM scheduling called the Precedence Diagramming Method (PDM).  In addition to the “Finish-to-Start” relationship of basic CPM scheduling, PDM allows “Start-to-Start,” “Finish-to-Finish,” and “Start-to-Finish” relationships, all with or without lags.  While PDM software allows more realistic and more efficient modeling of real-world project schedules, it is possible for activities to have both predecessors and successors yet still suffer from dangling – hence inadequate – schedule logic.  These cases – generally categorized as dangling finish and dangling start – are also known as “orphan relationships.”

Dangling Finish

Consider the following three activities taken from a conceptual schedule for a civil construction project.  The project will take place on land that has been intentionally surcharged (pre-loaded with piles of soil) to strengthen the underlying materials.  The conceptual plan for the three activities is simple: 1) Push/roll-off the surcharge material to adjacent areas; 2) Perform grading and quality-assurance testing of the ground; 3) Construct concrete foundations for the buildings.

 

Because these activities are spread over a large area, it is possible to start the grading before completing the roll-over and to start the foundations before completing the grading.  The scheduler has modeled these relationships (in MSP) as SS+50% – that is the successor may start only after the predecessor has started, but with an additional lag of 50% of the predecessor’s duration (computed according to the successor’s calendar).  These activities, relationships, and the resulting (early) scheduled dates seem to reflect a true and achievable plan for prosecuting the work, meeting the first objective of a logic-driven schedule.

If the activities fail to progress as initially planned, however, then the schedule may not accurately forecast the consequences.  If the Roll-Over takes longer than expected, then this delay may in fact affect completion of the Rough-grading task and, eventually, the foundation construction and its successors.  The schedule model fails to account for these extended finishes, however, and may forecast outcomes that are physically impossible – such as building foundations being constructed in areas where the surcharge material has not yet been removed.

When the indefinite delay of an activity’s finish has no logical consequences for any other activity, then the activity has a “dangling finish” – representing incomplete logical development of the schedule.  In a PDM schedule, any activity with ONLY SS or SF successors has a dangling finish.  Such dangling finishes are called “open finishes” in Acumen Fuse, a 3rd party diagnostic tool.

Dangling Start

The same three activities could be modeled instead using Finish-to-Finish relationships to arrive at identical dates.

If subsequent schedule developments lead to longer durations for successor activities, the schedule model will respond by having them start earlier.  As a consequence, some schedule dates may occur at times that are physically impossible – such as starting rough grading before the first shovel of surcharge has been removed or (again) building foundations being constructed in areas where the surcharge material has not yet been removed.

When the indefinite acceleration of an activity’s start may be implemented without logical restraint from any other activity, then the activity has a “dangling start” – representing incomplete logical development of the schedule.  In a PDM schedule, any activity with ONLY FF or SF predecessors has a dangling start.  Such dangling starts are called “open starts” in Acumen Fuse.

Correction of Dangling Starts/Finishes

The examples shown are typical of overlapping activities with progressive feed relationships.  In such cases, it is common to implement a “ladder logic” scheduling model, where multiple parallel Start-to-Start and Finish-to-Finish relationships are imposed between related activities.  Such a model is easy to implement in P6.  In MSP – which prohibits parallel relationships between tasks – then dummy milestones are needed.

In a schedule model incorporating ladder logic, one of the two parallel relationships will drive the successor’s dates, depending on the relative durations and lags.  In the example below, the Rough grading activity is driven by its Start-to-Start relationship with Roll-over.  Because Rough grading has been extended, however, the subsequent Foundations construction is delayed (and driven) by the Finish-to-Finish relationship from Rough grading.  This represents robust logic development between the activities.

In general, dangling starts/finishes are avoided by explicit inclusion of all legitimate technological and/or resource constraints in the schedule model, even where the resulting relationships are not obviously driving successor activities.  This is, of course, the basis of all robust logic-driven scheduling practice.

Finding Dangling Starts/Finishes

Until recently, detecting and isolating dangling starts and finishes was not an easy process for users in either MSP or P6.  In both tools, the preferred approach is to specify an activity/task filter to show only those activities that:

  • For Dangling Starts –
    • Have some predecessors, and
    • Have NO FS or SS predecessors.
  • For Dangling Finishes –
    • Have some successors, and
    • Have NO FS or FF successors.

In MSP, each task includes a “predecessors” field listing the Task ID, relationship type, and lag for each predecessor relationship.  The task “successors” field lists the same information for successor relationships.  Unfortunately, the default relationship type – FS – is not explicitly listed in either field, and preparing a filter to exclude activities that contain FS relationships in one field or the other is not trivial, requiring several intermediate calculations.  Alternately, the user is left to manually inspect the predecessors and successors of each task, to export the project to Excel for analysis, or to use an add-in like Acumen Fuse or BPC Logic Filter to identify danglers.  [The add-ins examine the underlying relationship objects in the MSP database, which could also be done directly using a Project macro/vba.]

Similarly, each activity in a P6 schedule includes both “Predecessors” and “Successors” list fields, but these lists include only the IDs of the connected activities – relationship types are excluded.  P6 16.1 and later releases include two additional fields – Predecessor Details and Successor Details – that include relationship types and may be easily included in a filter specification using the above criteria.  Users who have not updated to P6 16.1 or later – and who do not have access to an add-in like Acumen Fuse or Steelray – may export the activity and relationship information to a spreadsheet for analysis.  (Spreadsheet analysis of the P6 data is generally more straightforward than for MSP.)

Consequences of Dangling Logic

The primary consequence of dangling logic in a project schedule is an initial/Baseline plan that is not reliable due to the omission of substantial sequential constraints.  For example, many fast-track design-build projects require the start of field work before the completion of engineering, and sometimes the final engineering works are either left dangling or are tied only to a generic project completion milestone.  The logical ties between certain engineering activities and the necessary quality assurance and commissioning activities may be inadvertently omitted.  Without complete logic, neither the early (CPM) dates nor the late dates for the project are reliable.  Total Float shown for the later engineering activities and for their latent/unlinked successors may be excessive.  Since Total Float and the Critical Path definition are unreliable as a result of missing logic, the Baseline project schedule does not provide a suitable basis for monitoring progress or for evaluating potential delays.

Many project schedules may appear acceptable at the time of Baseline review, but dangling starts and finishes can severely compromise their usefulness during the project execution.  This is ultimately because actual durations invariably differ from baseline durations, but the secondary relationships that are needed to ensure logic integrity are missing.  In other words, the schedule model fails to reflect the real consequences of activity delays that appear during schedule updates.  The flaws in the schedule logic become obvious, and credibility is lost.

Schedule Risk Analysis is aimed at quantifying, typically through simulation, the consequences of uncertainty in schedule durations.  Since the intent of a simulation is to repetitively reproduce the consequences of changed durations in the schedule, the model weaknesses that affect the schedule update process also affect the outcome of the simulation.  Therefore, risk simulation of a project schedule with dangling logic is not reliable.

Terminology for Dangling Logic

Dangling logic – and particularly dangling starts and finishes – have been identified as such in the literature for at least 10-15 years.  See http://www.projectrisk.com/white_papers/The_Problem_with_Dangling_Activities_in_Project_Schedules.pdf.

Although the two concepts of dangling logic described here (i.e. the CPM and PDM varieties) are fairly straightforward, there is not uniform agreement on the terminology.

The Practice Standard for Scheduling, Second Edition (2011), published by the Project Management Institute (PMI) limits its “dangling” logic discussion to the PDM variety.  It describes “dangling” activities as activities that don’t “have an FS or SS predecessor and an FS or FF successor.”  In this standard, “Open-Ended Activities” include those “lacking either a predecessor or a successor or both.”  Thus, while not explicitly stated, “Open-Ended Activities” are a subset of dangling activities.

PMI’s Scheduling Excellence Initiative Committee has described a dangling activity somewhat vaguely.  The Committee’s CPM Scheduling for Construction: Best Practices and Guidelines (published by PMI, 2014) provides the following definition – “Dangling Activity: An activity tied from only one end (start or finish). A dangling activity has only a predecessor(s) or successor(s), not both.”  This definition clearly combines the two concepts without distinguishing between them.  “Dangling” references in the text are limited to the CPM, or open-ends, concept.

CPM in Construction Management, Eighth Edition (2016), a graduate-level textbook and respected reference book for serious construction planners and schedulers, contains only a single reference to “dangling activities” as something to be precluded.  It does not otherwise describe or define them.  The book briefly discusses dangling starts/finishes as a problem unique to PDM schedules, but it uses the term “orphaned relationships” rather than “dangling”.

The US’s Government Accounting Office (GAO) and Defense Contract Management Agency (DCMA) both align with the PMI practice standard, describing dangling activities according to the PDM concept.  From GAO-16-89G, Schedule Assessment Guide; Best Practices for Project Schedules (2015) – “Dangling activities: number of remaining detail activities and milestones with no predecessor on start date” and “Dangling activities: number of remaining detail activities and milestones with no successor off finish date.”  Open-ended logic (i.e. the CPM variety of dangling logic) is simply identified as “missing logic,” “missing predecessors,” or “missing successors.”

The Planning & Scheduling Excellence Guide (PASEG v3, 2016), published by the National Defense Industry Association,  includes a brief section on Open Ended Tasks among things to avoid in its chapter on Horizontal Traceability.  This section mentions “dangling logic” (specifically a dangling finish) as something to be avoided because it invalidates schedule risk assessment.  Neither term is formally defined in the guide.

AACE International (formerly the Association for Cost Engineering) publishes a number of recommended practices (RPs) related to project scheduling.  Unfortunately RP 10S-90: Cost Engineering Terminology (which is routinely updated to reflect the development of related standards and RPs) includes a definition for “Open-Ended Activities” only.  It ignores dangling logic of the PDM variety.

Dangling Logic in BPC Logic Filter

Users of BPC Logic Filter for Microsoft Project can execute the Project Logic Checker to isolate dangling logic and other issues affecting project schedule integrity.  The PMI/GAO definitions are used.  This figure shows the same schedule depicted in the network diagram at the beginning of this post – after running the Project Logic Checker.  The five “No Predecessors” and two “No Successors” tasks (including start and finish milestones) are clearly tagged and summarized, as are two dangling-finish tasks.

Modeling Waiting Times in Microsoft Project

Mandatory waiting times between certain tasks are a common feature of many project schedules.  In construction, the typical example is concrete curing time.  That is the time interval (typically under a week) after a batch of concrete is placed but before it gains sufficient strength to remove/strip the formwork and continue working.  Similar wait times can be required in non-construction projects. Common features of such waiting times are:

  • The waiting time is not associated with productive work;
  • The waiting time is independent of any Project, Task, or Resource calendar.  That is, it takes place around the clock, independent of weekends and holidays.

For a 5-day curing time in a Microsoft Project (MSP) schedule – between concrete placement and form stripping – there are four obvious modeling techniques:

  1. Create a “cure” task with a “5-day” duration and assign a 7-day x 24-hour calendar to the task.
  2. Create a “cure” task and assign a duration of 5 “elapsed” days.
  3. Don’t create a “cure” task.  Instead model the curing time as a 5-elapsed-day lag between the “place concrete” and “strip forms” tasks.
  4. Create a “cure” task with a 5-day duration and assign a modified 7-day weekly calendar to the task.

As shown in the figures, all four techniques can be used to generate the same (early) schedule dates for the project.  Which technique to use depends on a few factors.

  •  Within MSP, a “day” is fundamentally defined according to the “hours per day” setting for the project, and any “day” entries are automatically converted to minutes using that setting.  With default settings, one “day” is 8 hours (i.e. 480 minutes).  This can lead to confusion when calendars are changed or assigned without taking the setting into account.  For example, when a 24-hour calendar is assigned to a 3-day-duration task in a project with default (i.e. 8 hours/day) settings, then the task will finish in 24 hours (i.e. 1 calendar day).   Under the same conditions, a curing time of 5 calendar days (i.e. 120 hours) would require a specified task “duration” of 120/8 = 15 days.  To minimize such confusion, it is a good practice to specify durations in hours when 24-hour calendars are applied, as shown in the figure.
  • For most purposes, assigning an “elapsed days” duration is functionally equivalent to applying a 24-hour calendar to the task and making the necessary duration adjustments.  This can reduce confusion associated with the hours per day setting.  The two techniques yield identical results in the example.
  •  Using an elapsed-lag instead of a dedicated task is functionally simple to implement, and many project schedulers routinely use this approach.  Nevertheless, lags are generally discouraged or prohibited by some scheduling specifications and recommended practices for good reasons.  Chiefly, lags can substantially affect schedule dates while remaining relatively invisible on typical schedule documents – this makes them easy to abuse for date-manipulation.  In addition, unlike tasks, lags are not easily incorporated into external algorithms for evaluation or manipulation of project schedules – e.g. for risk simulation. This can substantially degrade the value of such algorithms.
  • Total Slack calculations are substantially complicated by the impacts of multiple calendars (including the use of elapsed durations).  Since MSP relies solely on Total Slack to identify “Critical” tasks, the true Critical Path for the project can be inadequately described for any of these techniques.  For example, when the curing time finishes at the end of a workday in the middle of the work week, the “cure” task (on a 24-hour calendar) possesses 15 hours of Total Slack – MSP therefore excludes it from the Critical Path.  If instead of a 24-hour calendar, a modified (i.e. 7d x 8h, no-weekend) calendar is applied to the curing task, then the positive Total Slack is eliminated in this case, and the Critical Path is correct.  (This is shown at the top of the figure below.)  Unfortunately, the modified calendar is no better than the others if the curing time finishes on the weekend.  The 1 day of Total Slack causes the Critical Path to be truncated.  (See the lower half of the figure below.) 

Unfortunately, the only out-of-the-box method to ensure that the entire critical path is captured is to raise the Total Slack threshold from the default value (zero) to some number that is judged high enough to capture all the truly critical tasks. I have found such an approach unsatisfactory for a variety of reasons.  In any case, the true Critical Path – i.e. the driving logical path to project completion – remains obscured.

Fortunately, the Longest Path algorithm in BPC Logic Filter is indifferent to which modeling approach is used.  As shown in the figure below, the driving logical paths are correctly identified for each case.  (The number to the right of each bar is the task’s path relative float with respect to the project completion task – zero for the longest path.  BPC Logic Filter typically depicts logical driving paths with a dark red bar.)

Inspecting Task Links with BPC Logic Filter for Microsoft Project

BPC Logic Filter – an add-in for Microsoft Project (desktop) – includes an advanced Logic Inspector feature to greatly simplify the examination and navigation of logic-driven schedule activities.

When building or managing a complex project schedule, it’s often necessary to examine the logical relationships between tasks for a variety of reasons.  Particular questions for any given task include:

  1. What other tasks must finish (or start) before this task may start (or finish)? (i.e. what are its predecessors and how are they related?)
  2. Of all the task’s predecessors, which ones are actually controlling the scheduled dates for this task? – i.e. what are its driving predecessors?
  3. For the task’s non-driving predecessors, how much may each be allowed to slip before it becomes driving (for this task)? – i.e. what is the relative float?
  4. a)What other tasks must wait for this task to finish (or start) before they can proceed? – i.e. what are its successors?  b)Which successors are driven? c)How much relative float exists?

For users of Microsoft Project (MSP), questions 1 and 4a are most easily answered using the “Predecessors and Successors” view of one of the Task Forms in the lower pane.  For simple schedules, question 2 can be answered by the “Predecessors” list of the Task Inspector pane.  For more complex schedules – and for all other questions – the user must visually cross-reference the scheduled dates of the various linked tasks from several views, estimating relative floats and identifying driving relationships.  This can be time consuming and error prone.  Beginning with the 2013 version, MSP provides “Task Path” bar styles, which visually identify driving and non-driving predecessor and successor paths (i.e. logically connected task chains) of any selected task on the bar chart.  These can be difficult to read, however, when the project logic is complex.

BPC Logic Filter has always answered these questions on the way to visualizing logic flow through a schedule, and several of the tracer analyses can be easily customized to examine only a single task and its links.  Since the tracers generally apply a custom filter to the schedule, however, the time to examine a single task could become unwieldy for a very large project.

The native MSP predecessor and successor tables provide only limited information: ID, Name, Type, and Lag – all sorted according to the order the links were initially created.  Here they are shown as part of the Task Details Form.

Clicking BPC’s Logic Inspector creates two new floating windows listing the predecessors and successors of the selected task.

In contrast to the native forms, Logic Inspector provides a richer table: sorting the links according to relative float, highlighting driving links at the top of the table, and identifying links to inactive tasks at the bottom. Scheduled dates, Percent Complete, Total Slack, Task Calendars, and Resources of the linked tasks are also shown by default for easier confirmation and communication of relative float results.  (If desired, the latter two fields can be replaced by user-selected fields from the current task table.)

Logic-related fields for the selected task – Total Slack, Constraints, Deadlines, Start/Finish dates, Resources, and Calendar – are included for reference above the table.  Colored highlighting is used to emphasize those fields with notable influence on the current schedule.  E.g. effective constraints, violated Deadlines, Actualized dates, leveled resources.

The JUMP button allows logic-based navigation forward and backward through the schedule network one task at a time.  Jumping to another task using the button automatically updates the predecessor and successor forms.  Driving relationships are selected by default, but any relationship can be selected and explored.  To keep things simple, you can’t jump to a task that is hidden (by a filter or outline selection) nor to a task in another project window.

Since implementation, I’ve found Logic Inspector to be an invaluable – and fast – complement to the rest of the features in BPC Logic Filter.  The two new windows are passive readers of existing project data; they are not for adding, removing, or modifying relationships.  MSP already provides a number of different approaches there.

Check out the video here to see the feature in action.

Using Logic Inspector to examine resource drivers is addressed in another post.

Microsoft Project Schedule Health Checking and Fixing using BPC Logic Filter

Regular users of BPC Logic Filter will have noticed some modest changes with the recent release of version 1.2.  The ribbon has been slightly revised, and two new buttons have been added: “Project Logic Checker” and “Logic Quick Check”. The second is essentially an abbreviated version of the first.

The Project Logic Checker examines every task in the project and flags the following logic issues for closer review or action:

Task Definition Issues
  • Manually-scheduled tasks (By definition, these are incompatible with logic-driven scheduling.)
  • Inactive tasks (In MSP 2010, these are essentially ignored. In MSP 2013+ they are essentially included in the schedule calculations as zero-duration tasks.)
  • External tasks and external links (Scheduling of tasks with external links can change depending on whether the source schedules of the external tasks are available and open.)
  • (Hammock) tasks made with OLE links (OLE links typically impose persistent logic constraints.)
  • Summary tasks with Logic (Hierarchical logic can override precedence logic in the schedule calculations and cause confusion.)
  • Tasks with Logic on Parent Summaries  (These tasks may be controlled by non-precedence logic.)
  • Constraints and Deadlines (“Must Start/Finish On” constraints are “Hard” constraints since they can override logic.  In addition, “Start/Finish No Later Than” constraints are included as “Hard” constraints ONLY when “Tasks will always honor their constraint dates” is checked (i.e. the default value).  These are always “Hard” constraints according to 2009 DCMA 14-Point Assessment guidance.)
  • Duplicate Task Names (Duplicate task names force reliance on a task’s outline hierarchy for recognition of task scope.  Development and analysis of the project logic then becomes inefficient or impossible.)    
TASK Relationship ISSUES
  • Missing logic; that is “Open Ends,” including Dangling Starts and Finishes.  (Schedules with these conditions are unreliable.)
  • Relationship Lags and Leads (i.e. negative lags) that that are excessive with respect to the associated task durations (Ideally, logic driven schedules use explicit tasks for all time-consuming activities.  Substantial leads and lags are incompatible with schedule risk assessment and are generally considered poor practice.)
  • Relationships that are not Finish-to-Start (Some scheduling philosophies mandate only Finish-to-Start relationships.)
  • Relationships that are Start-to-Finish (These relationships are extremely rare in actual project schedules, but they are often used incorrectly.)
  • Merge Points in the schedule (i.e. tasks with a high number of immediate predecessors)
  • Reverse Logic Flow through the task’s duration; i.e. shortening the task delays the successor, and lengthening the task may accelerate the successor.  (See this entry).
  • Neutral Logic Flow through the task’s duration; i.e. shortening or lengthening the task has no impact on the successor.
  • Links to inactive tasks  (Depending on the MSP version being used, such links can alter the schedule unexpectedly.)
Task Update ISSUES
  • Invalid Dates, including incomplete work in the past and completed work in the future (with respect to the Status Date)
  • Splits
  • Out-of-sequence progress
  • Tasks that have missed their target/baseline finish date (as of the status date.)
Other TASK ISSUES
  • Overlong task durations
  • False Milestones (i.e. “Milestones” with non-zero durations)
  • Excessive or negative values for Total Slack

Users can include or exclude any desired checks from the analysis – or adjust associated thresholds – using the Checker Preferences.

The tool automatically restricts the view to show only tasks with logic issues, then it presents an output form that a) summarizes the analysis, and b) allows the user to dynamically modify the filter for pinpoint focus.

For example, here is a highly summarized, ~3300-task, proposed recovery schedule for a troubled international construction project. The Settings window confirms that the logic checker will examine most non-resource-related issues but will ignore the long-duration and high-slack checks for now.

Running the Project Logic Checker identifies and presents over 1500 tasks with logic issues (perhaps a hint to the source of the project’s “troubles.”) The user can then use the output form to reduce or expand the view.

Here’s a close-up of the output/filter form, slightly improved from the one shown in the other figures:

For example, by un-checking all but the Dangling Start box and then clicking filter, I can choose to see only the tasks with Dangling Starts, i.e. tasks with predecessors but without start-predecessors.

Then, I can check only the False Milestones box to see – and correct – the 17 tasks that are coded as milestones but possess a non-zero duration.

Of course, if I’m only interested in one issue – Logic on Summary Tasks for example, than I can begin by excluding all the other issues from the analysis. The result is a (slightly) less cluttered picture.  This one highlights the four summary tasks with logic and the forty-four subtasks that are (or may be) affected.

The dynamic re-filtering requires full data persistence (in the general settings), and the bar labeling only works if “Re-color Bars” is selected (in the bar settings).

For schedulers and schedule reviewers, the new Project Logic Checker provides an action-focused basic schedule health check functionality that can be leveraged off the various logic tracers included in the tool.  There is no fancy dashboard and no pass/fail metrics based on odd ratios.  For now I think I prefer it that way.

Macro for Tracing, Filtering, and Sorting Task Paths in Microsoft Project

Here are three macros (collectively called QuickTrace) to display the logical predecessors or successors (or both) of the selected task – filtering out all others – and sorted by logical path.  The filter can be limited to show all logic or only “driving” logic.  There is also a highlight-only option.

With the apparent demise of Mike Dahlgren’s site, masamiki.com, his “Trace” macro seems to no longer be generally available.  (It’s also a violation of his site’s terms of use to re-distribute code that was obtained there.)  My entry on Listing Driving Predecessors has been getting a lot of traffic from people who (I suspect) are trying to find a variation of Trace.  In response to a question over at MPUG today, I decided to write up something – what I call QuickTrace – to generate similar output for sharing.  It is after all less than a hundred lines of code.

For determining driving relationships, QuickTrace relies on MSP’s “StartDriver” task object, the basis of the Task Inspector pane (and the Driving Predecessors highlighter in MSP 2013+).  This is a substantial improvement over the original Trace macro, which used Free Slack as the driving indicator.  Still, I’ve found StartDriver to be unreliable in the presence of non-FS relationships (See here.)  BPC Logic Filter (our MSP Add-In) instead identifies driving relationships directly by computing and examining relationship free floats – quite a bit more involved.

[Jan’19 Edit: QuickTrace also relies on recursion (a sort of repeated self-cloning process), and this makes it susceptible to crashing if the path length (in number of tasks) is too long.  In MSP 2010, I’ve analyzed path lengths a bit over 4,000 tasks before crashing.  The same analysis in MSP 2016 leads to a crash after only 700 tasks.

Version 1.5 of BPC Logic Filter now includes a QuickTrace option.

This implements the same recursive tracing algorithm that I’ve included in the macro code.  It’s blazing fast, and its results are perfectly aligned with the Task Path bar styles of MSP 2013+, no matter how flawed.  It also handles much longer path lengths (just under 8,000 tasks in MSP 2016) before running out of memory.]

Here’s the code. There are basically three front-end macros that you can assign buttons or hot keys to, one for predecessor chains, one for successor chains, and one for both.  (Using the last one can make the resulting path sort a little jumbled, so I made re-sorting optional.)    These call the other procedures to a) collect user input; b) clear existing values in the Flag4 and Number5 fields; c) recursively run through the chains of related tasks and and mark them using those fields; d) apply the filter and sort using those fields; and e) display a message box summarizing the filter/highlighting.  Note, this is provided as-is and is not supported by anyone.  I have not taken the time to accommodate every possible situation and won’t be doing so in the future.  If you are new to vba, please google around a bit before asking questions that are already answered somewhere else – that includes, “how do I install this and make it work?”  (Short answer: copy and paste the entire block into a new module in the visual basic editor.  Then add the three front-end macros to a custom group on one or more of your ribbon tabs.)

'QuickTrace Module
'Coded by T.Boyle, PE, PSP on 16Mar'17 [25Sep'18 edits - to allow highlighting, to provide a descriptive message box
'   after running, and to streamline the code.]  This Module is intended to trace logical paths from the selected task
'   to all of its predecessors or successors, then show only related tasks.  Tasks are sorted in the order of analysis,
'   which generally corresponds to identified logical "paths".
'CAVEATS:
'   1. This code WILL OVER-WRITE fields FLAG4 and NUMBER5.  Make sure these fields are not needed before running.  Otherwise,
'      edit the code to use different fields, as shown below.
'   2. This code relies on the StartDriver object for defining driving path logic.  It may not always be reliable for non FS
'      relationships.
'   3. Install all code into a new module, with "QuickTrace Module" above as the top line.
'   4. Assign buttons or hotkeys to the first three procedures only (the others are called by these three):
        'a. CallQTraceP() - Traces predecessors.
        'b. CallQTraceS() - Traces successors.
        'c. CallQTraceB() - Traces both predecessors and successors (Added 15Nov'17)
'
 
Option Explicit
Private Cnt As Long, Driv As Boolean, HL As Boolean, ShowSums As Boolean, Tsel As Task, DirGlob As String
 
Sub CallQTraceP()
    'This procedure finds, marks, filters, and sorts predecessors of the selected task.
    'Run this directly using a button or hot key
     
    Cnt = 0
    DirGlob = "P"
        
    ClearFields
    CollectInput
    'Run Trace from Selected cell
    Call QTrace(Tsel, "P")
    Call Filter("P")
 
End Sub
 
Sub CallQTraceS()
    'This procedure finds, marks, filters, and sorts successors of the selected task.
    'Run this directly using a button or hot key
     
    Cnt = 0
    DirGlob = "S"
        
    ClearFields
    CollectInput
    'Run Trace from Selected cell
    Call QTrace(Tsel, "S")
    Call Filter("S")
 
End Sub
 
Sub CallQTraceB()
    'This procedure finds, marks, filters, and sorts both predecessors and successors of the selected task.
    'Run this directly using a button or hot key
     
    Cnt = 0
    DirGlob = "B"
        
    ClearFields
    CollectInput
    'Run Trace from Selected cell
    Call QTrace(Tsel, "P")
    Call QTrace(Tsel, "S")
    Call Filter("P")
 
End Sub
 
Sub QTrace(ByRef t As Task, ByVal dir As String)
    'This procedure marks a task (as related) and calls itself for each related predecessor or successor.
    'This procedure is called by another procedure.
     
    Dim d As TaskDependency
    Dim ds As TaskDependency
     
    'Mark this task as related
    Cnt = Cnt + 1
    '''''''''''''''''''''''''''''''''''''''''''''Edit Fields Flag4 and Number5 as Needed'''''''''''''''''''''''''''''''''''''''''
    t.Flag4 = True
    t.Number5 = Cnt
    '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
     
    'Recurse to next dependency
    If Driv Then
        If dir = "P" Then
            For Each d In t.StartDriver.PredecessorDrivers
                Call QTrace(d.From, "P")
            Next d
        Else 'i.e. dir="S"
            For Each ds In t.TaskDependencies
                If ds.From = t Then
                    For Each d In ds.To.StartDriver.PredecessorDrivers
                        If d.From = t Then Call QTrace(d.To, "S")
                    Next d
                End If
            Next ds
        End If
    Else
        For Each d In t.TaskDependencies
            If dir = "P" And d.To = t Then Call QTrace(d.From, "P")
            If dir = "S" And d.From = t Then Call QTrace(d.To, "S")
        Next d
    End If
End Sub
 
Sub CollectInput()
    'This procedure collects user input.
    'This procedure is called by another procedure.

    Driv = False
    HL = False
    ShowSums = False
    
    Set Tsel = ActiveCell.Task
    If MsgBox("Driving Path only?", vbYesNo) = vbYes Then Driv = True
    If MsgBox("Highlight only?", vbYesNo) = vbYes Then
        HL = True
    Else
        If MsgBox("Show Summary Tasks?", vbYesNo) = vbYes Then ShowSums = True
    End If

End Sub
Sub ClearFields()
    'This procedure runs through the tasks of the active project and clears two selected fields for use.
    'This procedure is called by another procedure.
     
    Dim t As Task
    'Clear Fields
    For Each t In ActiveProject.Tasks
        If Not t Is Nothing Then
    '''''''''''''''''''''''''''''''''''''''''''''Edit Fields Flag4 and Number5 as Needed'''''''''''''''''''''''''''''''''''''''''
            t.Flag4 = False
            t.Number5 = 0
    '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
        End If
    Next t
End Sub
 
Sub Filter(ByVal dir As String)
    'This procedure creates and applies a filter to show only related tasks.
    'This procedure is called by another procedure.
     
            '''''''''''''''''''''''''''''''''''''''''''''Edit Field Flag4 as Needed'''''''''''''''''''''''''''''''''''''''''
            FilterEdit Name:="Flag4", TaskFilter:=True, Create:=True, _
                OverwriteExisting:=True, FieldName:="Flag4", Test:="equals", _
                Value:="Yes", ShowInMenu:=True, ShowSummaryTasks:=ShowSums
            FilterApply Name:="Flag4", Highlight:=HL
            '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
        
        If ShowSums Then '(HL is False)
            'Sort by path order
            If MsgBox("Resort to show paths?", vbYesNo) = vbYes Then
            '''''''''''''''''''''''''''''''''''''''''''''Edit Field Number5 as Needed'''''''''''''''''''''''''''''''''''''''''
                If dir = "P" Then Sort Key1:="Number5", Ascending1:=False, Renumber:=False, Outline:=True
                If dir = "S" Then Sort Key1:="Number5", Ascending1:=True, Renumber:=False, Outline:=True
            '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
            End If
        Else '(ShowSums is False and HL may be true or false)
            If Not HL Then
            'Sort by path order
                If MsgBox("Resort to show paths?", vbYesNo) = vbYes Then
            '''''''''''''''''''''''''''''''''''''''''''''Edit Field Number5 as Needed'''''''''''''''''''''''''''''''''''''''''
                    If dir = "P" Then Sort Key1:="Number5", Ascending1:=False, Renumber:=False, Outline:=False
                    If dir = "S" Then Sort Key1:="Number5", Ascending1:=True, Renumber:=False, Outline:=False
            '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
                End If
            End If
        End If
        EditGoTo ID:=Tsel.ID
        FilterBox
End Sub
        
Sub FilterBox()
    'This procedure creates and displays a message box describing the filter/highlight basis.
    'This procedure is called by another procedure.
    Dim Msg As String
    
    If HL Then
        Msg = "Highlighting "
    Else
        Msg = "Filtering for "
    End If
    
    Select Case DirGlob
        Case "P"
            If Driv Then Msg = Msg & "driving "
            Msg = Msg & "predecessors "
        Case "S"
            If Driv Then Msg = Msg & "driven "
            Msg = Msg & "successors "
        Case "B"
            If Driv Then Msg = Msg & "driving & driven "
            Msg = Msg & "predecessors & successors "
    End Select
    
    Msg = Msg & "of task " & Tsel.ID & ": " & Tsel.Name & " (inclusive)"
    MsgBox Msg
    
End Sub


[Aug’18 Edit:] One of the commentators sent an example of a schedule where the macro includes in the driving path to project completion two tasks that are in fact neither critical nor driving .  As shown below, the Task Path functionality is used to highlight the “Driving Predecessors” to Task 13 (orange bars).

Tasks 21 and 22 are included in the Task Path highlighting, and they are also flagged as part of the Driving Path (to Task 13) by the QuickTrace macros.  This is because MSP has marked Task 22 as the StartDriver predecessor for Task 26.  As a manually-scheduled task, however, Task 26 really has NO StartDriver predecessor, and the reference to Task 22 is incorrect.  Neither the macro nor the Task Path function has been adapted to account for this.  (BPC Logic Filter correctly excludes these non-driving tasks, and MSP marks them as non-critical because they possess positive Total Slack.)

Troubleshooting Circular Task Relationships with BPC Logic Filter

Planners attempting to build complex project schedules in Microsoft Project will typically come across the circular logic warning at some point when trying to link tasks.

In general, most such messages come from assigning logic to summary tasks, which experienced schedulers don’t do.

When an experienced scheduler encounters the circular logic warning, it often means that he has made an earlier error in the logic that is only now being detected as the loop is closed.  For example, a normal construction “fragnet” for concrete structures may include the following task sequence: Form -> Pour -> Finish -> Cure – > Strip(forms), repeated over and over for different structures on the project. If I get the warning when trying to impose one of these obvious links – say from Pour to Finish, then I know that Pour and Finish are already connected.  I have to find the logical error in that path of task connections.

Fortunately,  BPC Logic Filter includes a little feature that’s been variously referred to as “Bounded Network Analysis,” “Truncated Logic Tracing,” and “Logic Tracing to Target.”  It finds all the connections between any two tasks in the project and filters out all the others.  This makes finding the error that much easier.  The figure below highlights the selected task (Form3) in yellow and the target task (Pour3) in orange.  In the example, I can trace the problem linking Form3 and Pour3 to a “dummy string” of tasks that was inserted between Cure3 and Cure2.

Early last year I wrote about a method for finding the connections between two arbitrary activities in a CPM schedule.  Most of that post was aimed at using the circular logic error handler in Oracle Primavera P6 to accomplish the objective.  Obviously, this turns that method around.

Video – Find the Driving Path for Key Milestones in Microsoft Project using BPC Logic Filter

In the presence of Deadlines, Constraints, variable Calendars, and resource leveling, Total Slack becomes unreliable as an indicator of the Critical Path (or of nearness to the Critical Path).  In addition, many projects include Key Completion Milestones that occur long before the final scheduled activity of the project, so a Longest-Path approach doesn’t apply.  For these projects, I use the Task Logic Tracer to find the Driving Path and Near-Driving Paths of each Key Completion Milestone.