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Logic

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Joanne Foster
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interested in others thoughts on:

- top down vs bottom up scheduling, which do you use and why

I have always scheduled bottom up and sanity checked the results against what the project manager/project engineers expectations are. Currently there is a push in my company to top down schedule and progressively add logic to all levels of the schedule, the lowest level of logic is to be at work package level, and tasks below that must only be linked within the work package - which to my mind is not really going to work too well.

- do you allow logic at multiple levels of the schedule

I ensure that all logic is at the lowest level, this allows for the critical path to be visible at the activity level, I also find that having logic at multiple levels causes endless issues when progressing not to plan and locating issues within the schedule.

- your thoughts on Finish to Start logic with negative lag

This has to be one of my pet hates, except for scheduling in procurement lead times, even then I generally drive the purchasing activity from another predecessor eg design review and have the successor with the +ve lag (lead time) where possible.

would love to hear thoughts on this from other experienced schedulers.

Thanks
J

Replies

Thank you, Alex.
I have not seen P3e 4.0 yet. I think that this feature is quite necessary especially in construction projects and it is good that it was added.
It is strange that on this site many people criticized P3e for much less problems but not for this huge one. Now P3e 4.0 users will be able to calculate the cost of the materials consumed in their projects.
But I just cannot imagine how P3e 3.5 users manage construction project budgets if the cost of materials is not available.
Vladimir
Alex Wong
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Vladimir,

You are right, in version 4.0 Primavera included a resource as materials

Cheers

Alex
Luca,
one thing with the export from Spider to P3e cause huge and strange problem that I hope will be solved in P3e version 4.0.
We did not find such thing as the cost of material unit in P3e. We export assigned material quantity but its cost is exported into fixed activity cost.
I cannot imagine how to manage construction project budget without material costs, without controlling material flows, etc.
Maybe we don’t know where to find.
Vladimir
Alex,
it is a hard task. I am sure that PM software should be supported on site. It is not the same as promoting word processor. We want to be sure that our customers use Spider Project properly and as in Russia using Spider Project means a good project management in the company. We start to sell at the new markets if we have good partners there. Now we have such partners in Ukraine, Belorussia, Romania. We also sell the package to people from other countries who had found the package in the Internet - usually these people have proper qualification and we keep the contact and support them not only answering the questions but suggesting our advises on methodology and project management issues.
Entering other markets without local partners in a proper way (with local representatives, courses, support, promotion) is too expensive. We are not that rich and too busy because the Russian market is very fast growing. In 1993 when the first Spider version was suggested to the local market few people had the knowledge of what is project management. Now project management is hot. More and more companies implement PM and besides here Spider Project is used for resource management in manufacturing.
But you are right - we shall think about it and make more efforts in finding proper partners abroad.
Best Regards,
Vladimir
Alex Wong
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Vladimir

It seems that Spider have a great potentials, you should promot it to the rest of the project management world.

So that we can have an alternative.

Cheers

Alex Wong
Luca,
here they use Spider and transfer projects to Primavera if the customer wants it. Nobody use both programs in parallel. Spider is more powerful, has many additional features and fields. As the result in this transfer some Spider data are lost. I mean activity volumes, resource productivities, cost components, assignment costs, resource material requirements, multiresources and assignment pools, additioanal WBS, etc. Transfering data back and forth you will not use many useful Spider Project features. The data exported into Primavera are transformed according to P3e capabilities. You can restore Spider data using references but it is an additional work.
So I don’t support an idea to use both systems in the same projects. Here people usually move to Spider when Primavera or Open Plan resource and cost management capabilities are not sufficient to their projects. Many Spider Project users started with using MS Project (as everywhere). It should be necessary, if the need is not conscious then changing the software tools does not make sense.
Luca Basile
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And the programme transfer from P3e to Spider and vice versa has not problem?
All the coding structures, resoruces can be transfered?

The other problem can be financial one.
The management can argue why to spend money for two "similar" tools.

The Client wants Primavera, so we have to use Primavera.

These were the terms of the discussion, taken not long time ago.



In Russia some foreign clients like Washington Group or Parsons also require the project information in P3e format. Those who use Spider just export projects to P3e for these customers.
There is another interesting problem about which I wrote previously. Internal schedule is not intended for the customers. The schedule you use for reporting to your partners and the schedule you use for setting tasks are different. In Spider Project you can use different schedules for the same project and just export performance data from one project model to another. You don’t need to enter project performance data several times.
Is this problem (parallel schedules) actual for everybody? What do you do?
Luca Basile
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I tried Spider and I found very useful.
The opportunity to define several WBS is of incredible help.
The other planner I show it were enthusiastic of some feature.

I had problem to convince my top management to have a look at it.
All our Clients require P3.
David,
you can download Spider Project Demo (40 tasks restriction) and User Guide from http://www.spiderproject.ru/spider_e.shtml and some corresponding publications from http://www.spiderproject.ru/publ_e.shtml#eng
Demo includes sample projects. I will be glad to answer your questions and to learn your opinion. Demo version does not include some features like export/import to and from MS Project and Primavera, work with Internet, but main functionality is full.
Pay attention to resource leveling. Spider Project optimizes resource constrained schedules and takes into account financial and supply restrictions. Create as many WBS for the same project as you need.
If you will think that the package cannot do something useful - just ask (my E-mail: v_liberzon@yahoo.com). Some solutions are not traditional.
Enjoy,
Vladimir
David Watters
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Seems I need to get out more!! I have only used MS Project and Primavera to date, and the features that you have told me about seem really interesting (% lags, Volume Lags etc)

Any hints on websites so I can do some background reading ?
To Joanne and David:
In Spider Project we use volume lags - if some volume was done then the next activity can be performed (for example - if 500 m of ditching was done then the welding can start).
It is more reliable than % lag - it is hard to define EV % complete collecting performance data.
The only example of SF relationship that we usually use:
Hammock (LOE) task (project management activity for an example) will finish after the project object will start to function (shop starts to earn money or something like that).
Vladimir
David,
I mean that the internal contractor schedule should include reserves and finish dates of major milestones in this Level 3 schedule should be earlier that the target dates for the same milestones defined by Level 1 and 2 schedules. Contractual dates should be used as the target dates in the Level 3 schedule, not the scheduled dates. The same about costs. Our approach is similar to the Critical Chain methodology though has differences too.
PM controls several targets - internal, contractual and others if necessary. I did not mean that the contract data should not be taken into account.
Usually we simulate risks and uncertainties and our status report may include the following:
current probability of meeting internal schedule target is 67%, contractual target - 82%, and success probability trends are positive three weeks in a row.
Especially it concerns costs - contractual costs include profit and the internal targets should be tighter. The PM team should be motivated to reach internal targets based on the internal corporate norms, not just contractual targets spending all the money and resources that were included in the contract cost.
David Watters
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I think your partly right, and alos partly wrong. But then is all a game isn’t it? Everyone does it differently.

Level 3 = Engineering CTRs for Each Platform

Level 2 = Key Activities for Each Discipline in each platfrom

Level 1 = Key Dates for each Platform

BUT where we differ, is that I do not believe that these should be separated from contractual detail.
All the contractual milestones and contingencies SHOULD be built into your plan. That way you can advise your own management and the client where REAL criticality exists.

Anyway, let me know what you think as this is getting inetersting!!

Joanne, was your last for me or Vladimir?



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Another question...I seem to be full of them lately

If Level 1 & 2 are provided by the customer...then what do you do when they don’t provide you with a WBS to start with?

Increasingly the customer I deal with leaves it to each of the competitors to propose a WBS during tendering phase.

Joanne
David,
thank you for your reply. But I still insist that levels 1 and 2 are not just roll ups but different schedules that define project contract targets. Internal schedules should have different target dates and costs that don’t allow for contingency and management reserves included in the contract schedules. If they are just roll ups then it is just a matter of reporting and the schedule is the same for all levels. Is it correct?
David Watters
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Correct. Our level 3 aschedule is and engineering design schedule, as detailed as it needs to be. Our Level 2 and One schedules are rolled up formats used for meetings where senior management do not want to wade throught reams of paper.

Down side is though, getting the correct message across with limited activities !!
Contract conditions define target dates and costs for major deliverables.
The internal working schedule created by the contractor should have reasonable reserves to be sure that the contract conditions will be met.
We usually define a set of targets - contract targets, management targets (include managenet and contingency reserves), project management team targets (include contingency reserves), project team targets (do not include reserves - optimistic schedule).
So if I understood correctly then Level 1 and Level 2 schedules are created for the contract negotiations and reporting and represent contract target dates of major deliverables. Working contractor schedule may be quite different.
MK TSE
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In China, Level 1 is named Milestone programme, most activities are in milestone activity type, stated the time frame, key dates, etc.
Level 2 is in Master programme, build some major scopes in activity type among milestone.
Level 3 will be the Detailed Works programme.

Both Level 1 and 2 are prepared by client side and Level 3 is by contractor.
Joanne,
this is an interesting question - what is level 3 schedule? I don’t understand why there is a need to create schedule levels. You can present a reports with the different levels of detail - to show 2, 3, 4th, etc. levels of WBS but in the same schedule!
Joanne Foster
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each of the deliverables would be the predecessors to the meeting and I would put FS+ve lag calculated based on the customers review period. This does of course cause it’s own issues when the customer decides they don’t need all the allocated time and therefore the +ve lag may no longer be valid. But when I baseline the schedule I ensure that all review periods are accounted for.

The only time I have used SF-ve lag is for Agenda deliverable milestones, even then only for the Agenda for the Project Progress Review meetings with the customer. This is because the work to produce the agenda is part of the project management LOE task, and I’m not going to schedule a 30 minute task into my multi-million dollar project!...btw...I do believe this is dodgey scheduling...but i’ve gotten away with it in the past.

Just as a matter of interest what do you define as level 3 scheduling? For me, Level 3 schedule is one level below Work Package?
David Watters
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Okay - think of scheduling meetings into an engineering programme, say QA audits for Piping. These are usually time to coincide with the issue of certain deliverales, or studies. Do you think it would be good planning practive to use a FS-ve lag in such an instance to determine the timing of the meeting.

(Assume that the schedule is a Level 3 and connot be broken down any further.)

After reading the link from Joanne (and it was a good read! :¬) I would even be tempted to use SF, to allow the meting to be scheduled without being included in total float calcs.
Joanne Foster
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Alex

In the example you gave, I would not use F to S with negative lag, I would actually find a more appropriate predecessor ie the garden beds being ready for planting.

For the past 5 or so years I have dealt mainly with software development projects and never has anyone in that time managed to convince me that negative lag is appropriate - and A LOT have tried! It’s all in how you question the person providing the estimates as to whether you get the real answer. I challenge the Cost Account Managers on anything which I perceive as dodgey and occasionaly on those that aren’t, just to keep them on their toes.

each to his own I guess...

J
Alex Wong
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Joanne
I am not total agree with you on SS + Lag can be replace by FS - Lag

Ie if I have an activity where the original plan duration is 100 days and said I can only start the activity 50 days prior to it’s finish. ie 50 days before the store opening I will plant the flowers in the garden so that the flowers will blooming for the next 3 months after the opening date.

If base on what you stated I can use SS with + lag with 50 days. If I started the activity at day "1" and after 30 days the project manager told me that the opening date can be bring forward and he estimate the remaining durtion is 50 days and the activity is not 50% complete. Should I start plant the flowers?? with SS the logic , the activity will not start for another 20 days but if I use Finish to Start with -50 days then I should start.

I guess in real life if the activity is rely on the finish date then the logic better stay with the finish date. Because a plan is a plan once it kick off, conditions will vary and you may not remember the reason why you change the FS with a SS.

Again this problem can be solve by having the activity breakdown futher so that it become a FS without any lag.

Joanne Foster
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I use Open Plan Professional v3.0, I’m surprised that P3 doesn’t have that functionality.

As for Start to Finish....I have never been able to find an example of where it would be used, however it was discussed on the PMI College of Scheduling website http://www.pmicos.org/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=4;t=000022.

you might find that thread interesting.

Joanne
David Watters
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Yeh - seemed odd, BUt appeared to work. I take that the % lag you mention is a function of either P£e or some other planning package, as we don not have that facility in the version of P3 we use (3.1). But I like the idea.

SS+ve lag is always best as it is definable logic, even better to break it down further.

One other question I would love answered is has anyone ever used the SF link method in any schedule they know of. I was talking to my compadres in planning here in London, and they were keen to find out.
Joanne Foster
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The question I would ask is how did he calculate a negative lag in days?

IMHO negative lags are subjective opinions - which is my main issue with using them.

Whereas using Start to Start with a % lag, where the % lag is objectively calculated using the same basis that Earned Value is to be calculated.

For example - if you have 5 equal tasks within Work Package A (each having a weight of 20%) and once task 4 is finished Work Package B can start then your options are
FtoS with -ve lag, of however many days someone dreams up, or calculated based on the ’planned duration’ which may or may not become reality.
OR
StoS with 80% lag

(yes I do realise you could simply put the lower levels in the schedule, I was merely trying to give an example of how one could calculate objectively the % lag)
David Watters
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Recently cam across a sample of FS-ve lag that ’appeared’ to be usefull.

PDMS modelling for Piping on offshore structure on a Lev3l 3 plan.

PDMS is the computer model for the platform, progressed through various tages A thru to E with E being 100% in a stepped planned approach. Code E = 100% of Isos 100% complete

Each step was FS with a -ve lag, and as each step missed its planned completion, it drove out the overall completion date for the Code E activity, which in turn reforecast the Isos completion.

Seemed a bit odd to me but appeared to do the trick as it not possible to break the schedule out any further. The guy who developed it has got about 35yrs experience as well, and claimed it was a standard way of scheduling this work. Only problem was the lag - how did he know it was a given. Any thoughts?
Joanne Foster
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Hi Martin

If a Finish to Start logic can not be established, then a Start to Start with a Percentage Lag is what I would use, and therefore if the predecessor runs late it will push the start of the successor, and continue to do so until the predecessor meets the % value of the lag.

So if the relationship is Start to Start with 80% lag, then the successor can not start until it’s predecessor has a percent complete of 80%.

Hope that makes sense.

Joanne

Bernard Ertl
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Martin, IMO, because the relationship does not represent "hard logic".

I would try breaking the predecessor activity down into more detail where a logical FS relationship may be established.

Bernard Ertl
InterPlan Systems - eTaskMaker Project Planning Software
Martin Corkill
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Why is using negative lag on finish to start links bad scheduling practise ? What if I want to start snagging works 2 days before they finish in order to get things moving along quicker - would you use a start-start with positive lag ? That would be bad practise in my book as what happens if the task takes more (or less) time than originally planned ? The start-start link wouldn’t work then.
Joanne Foster
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Vladimir, could you please e-mail the pdf, as my pdf reader is not associating it with acrobat reader. my email is jjf_1975 at hotmail.com

Bernard, thanks for the link, I will have a read tomorrow.

I’m glad to hear the PMI is writing the standard for scheduling and will look forward to it’s publication.

Thanks for your comments.
Joanne
Bernard,
we create three project versions where not only activity durations, but also costs, material requirements, resources and events (and corresponding activities) may be different. And we analyze the total results for the whole project and its phases. An approach is similar to PERT though different too. Pessimistic schedule can include activities that are absent in the optimistic project scenario.
The main purpose - to control probability trends.
Best Regards,
Vladimir
Bernard Ertl
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Vladimir, how does your probablistic approach differ from PERT? It sounds like what you are describing.

Joanne, you may find this page interesting as it describes some of the shortcomings with PERT, Monte Carlo, etc. as risk analysis tools:

Scheduling with Uncertain Durations

FS relationships with negative lags (or SF relationships) do not represent hard logic for critical path analysis IMO. It is most often an artificial constraint used to gauge when to start a task for a JIT (just in time) process. In these cases, delaying tasks to the last moment it may distort float values and add risk to a project IMO. Sometimes that is acceptable depending upon business needs, but it is poor scheduling practice IMO.

Bernard Ertl
InterPlan Systems - eTaskMaker Project Planning Software
Thank you, Joanne, I understood your problem. Yes, Monte Carlo analysis does not work for large project networks because too many iterations are necessary. But it will not work with the phases too. Simulating different durations you should simulate different lags and different resource utilization. It is a poor approach and the results of the simulation will not be reliable.
We use different approach to risk simulation based on creating three project versions (optimistic, most probable and pessimistic) and approximizing probability distribution of the project results (time, cost, material requirements). In our projects it works perfectly. This approach was described in my recent presentation at the Australian Performance Management Symposium (http://www.spiderproject.ru/library/SDPM_Canberra2004.pdf)
It is used in many industries including Russian Ministry of Defense.
Monte Carlo simulation can be used for calculating necessary project contingency reserves and tracking their utilization. It is not easy and the results of simulation will not be reliable - so consider it just as an exersize for yourself. Unfortunately you should use both models in parallel. It is an additional work with the doubtful usefullness.
I am involved in the PMI group developing Practical Standard for Scheduling. In the discussions inside the group negative lags and start-finish relationships were considered as an indicators of the poor schedule.
It is clear from your postings that you don’t level resources. With the resource constraints the approach for top down scheduling that you described does not work at all.
Best Regards,
Vladimir
Joanne Foster
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why top down?...well...for Monte Carlo Analysis...yes...they want to change the entire way we schedule to satisfy one tool of project management...go figure *chuckle*

i’m not opposed to change, but i just can’t see how it’s going to work or make our jobs easier or better or even make our schedules more user friendly - so with no benefit other then it makes Monte Carlo Anlaysis easier, I’m miffed as to why we would even be going this way. I wanted to try and get ideas from outside the defence industry - which is why i posted on here.

the argument they have been using is "who says logic at the lowest level is correct?" and when we tried to explain that logic at the summary levels will introduce negative lags on almost every major phase and it will change possibly every month dependant on the subordinate tasks based on whether they track ahead or behind schedule I said "utilisation of negative lags is an indicator of a poorly constructed schedule, particularly when there is no real basis for the negative lag" and the response to that was "who says that negative lag is poor scheduling practice"

so it got me thinking - maybe I am wrong, but I haven’t been able to find any reference materials which details scheduling principles in enough detail or indeed a standard on the use of logic.

When I say negative lags I refer to negative lags between Requirements Analysis to Preliminary Design from Preliminary Design to Detailed Design...etc etc

I hope this makes sense
Alex,
why do you need resource constraints links if you can just level project resources. Having 5 teams you will receive corresponding schedule, for 4 teams - another one. It is easy.
Joanne,
"the idea of having both top down logic and bottom up logic within the one schedule" may work only if all project phases should be performed only one after another, or are completely independent. In the real life it is rare.

If you will create milestones for the start and finish events for project phases then top down logic will link these milestones. Usually we recommend to do it because in another WBS structure linked phases do not exist.

If some work package is typical we recommend to create corresponding fragnet that should be stored in the corporate fragnet library. If the fragnet is used in some project then it is taken from the library and is implemented in the project model. Then fragnet activities should be linked with the activities of other fragnets in the project. Creating fragnet library is a good idea, but linking the fragnets and not the activities within fragnets is a bad one.

Why top down logic became necessary in your company?
Joanne Foster
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Vladmir - thanks for you comments, it’s nice to think I wasn’t going completely loopy.

Alex - I found your post a little confusing, and this might be because my experience is in Software/Hardware projects as opposed to construction - so resource constrained logic is something that we don’t really use (and to be honest I had never heard of it until your post)

Given that I schedule software/hardware development projects - I have not had a single Cost Account Manager who has been able to successfully argue why a FtoS neg lag relationship could exist (outside of production activities) - so that may be where my mind set that that is poor logic comes from.

I understand the difference between top down and bottom up scheduling and when and where each may be appropriate, but I may not have made my question quite clear...in that my company are throwing around the idea of having both top down logic and bottom up logic within the one schedule, to me that’s like commiting a slow and painful project suicide.

any further comments on the topic would be appreciated.

Thanks
Joanne
Alex Wong
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Resource Constraints Logic

ie. say a contractor may decided to have 5 teams of workers to carryout 100 locations inidividually and each location take 10 days. If the schedule is breakdown into all 100 locations activities and the scheduler will linked them into five groups (5 teams) each will take 20 locations * 10 days = 200 days to finish the works. If each location is unique and your schedule is breakdown in to such details and track to these details then if anything out of synz, the scheduler require to reschedule the logic. In addition, during the EOT process the scheduler need to prove that the resource constraints is part of the critical path.
Alex,
please explain what is resource constraints logic?
Thank you,
Vladimir
Alex Wong
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interested in others thoughts on:

- top down vs bottom up scheduling, which do you use and why

Top down will be good when you have to produce a tender programme in a short time. In addition, it also give the scheduler some thought as on the overall plan (High level vision) Especially when a lot of the team member is not yet recurited or info is not accesible (Production rate...)the best way is top down. Remember if both top down and bottom up, 1 thing that is very critical is how deep you want the drew down the schedule and how much effort you can spend to maintain the schedule. I came across lot of schedule that actually when too far and at the end never mean anything to the project manager because it is too out of date and can run any simple analysis to the schedule. So the start is very important to develop any form of schedule.

- do you allow logic at multiple levels of the schedule

As I state above, depend how much time you allow to update your schedule. If you allow four weeks per month to update, "yes" multi level and resource contrainted logic can be added to the schedule. Remember you need to change all the resource contraints as the site progress changes. However,if you only allow 1 week of your time to do the update then try to min. the number of logic especially resource contraints logics.

- your thoughts on Finish to Start logic with negative lag

I think there are occasions that you will need to use FS with neg lag. like prepare in a cable manuf. line, the next batch of production will start preparation two days before the last batch complete. However, this logic can be reschedule if you add additional activity at the end of the production then you can have a start - start relation without any - lag. If you do this to all the logic, again you increase the no of activity without gaining any benefits.

I guess the logic will never use is start finish. (Any suggestion?? PPs)

would love to hear thoughts on this from other experienced schedulers.

Thanks
Ernesto Montales
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Vladimir,

Very well said.. I agree.


Regards

E. Montales
Joanne,
you are right - logic is on the activity (or task) level. Links between phases are too rough approximations of the real life. Besides using our software you can use multiple WBS for the same project and you just will not be able to control these links in the alternative WBS. You can create rough schedule and then decompose activities in more detail. In this case you should reconsider links - they still should be used on the lowest level of decomposition.
Negative lag is something that should be avoided. Sometimes it is still necessary to use them but these situations are rare and should be rare.
I think that you should demonstrate the examples when top down logic does not work to the senior management. It may be useful to receive their support.