Slashdot Log In
Can Software Schedules Be Estimated?
Posted by
timothy
on Mon Nov 05, 2001 10:03 AM
from the now-stop-abusing-the-mozilla-team dept.
from the now-stop-abusing-the-mozilla-team dept.
J.P.Lewis writes "
Is programming like manufacturing, or like physics?
We sometimes hear of enormous software projects that are
canceled after running years behind schedule.
On the other hand, there are software engineering methodologies
(inspired by similar methodologies in manufacturing)
that claim (or hint at) objective estimation
of project complexity and development schedules.
With objective schedule estimates, projects should never run late.
Are these failed software projects not using proper
software engineering, or is there a deeper problem?" Read on for one man's well-argued answer, which casts doubt on most software-delivery predictions, and hits on a few of the famous latecomers.
"A recent academic paper Large Limits to Software Estimation (ACM Software Engineering Notes, 26, no.4 2001) shows how software estimation can be interpreted in algorithmic (Kolmogorov) complexity terms. An algorithmic complexity variant of mathematical (Godel) incompleteness can then easily be interpreted as showing that all claims of purely objective estimation of project complexity, development time, and programmer productivity are incorrect. Software development is like physics: there is no objective way to know how long a program will take to develop."
Lewis also provides a link to this "introduction to incompleteness (a fun subject in itself) and other background material for the paper."
This discussion has been archived.
No new comments can be posted.
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
Full
Abbreviated
Hidden
Loading... please wait.
Software Schedules (Score:4, Funny)
1) As long as it takes.
2) Take your best estimate , and double it and add 5 or something....
It prefer the as long as it takes. Other wise you end up with something like Windows Me.
Re:Software Schedules (Score:3, Informative)
The standard multiplier used is PI.
There are also some interesting results of programming speed in the Prechelt's comparison of different programming languages: an article [ira.uka.de], a tech report [ira.uka.de].
One of the conclusions is that script languages such as Python or Perl are about 2-3 times as fast to program with than Java or C/C++, at least in the small projects. The script programs were also about half as long in lines. There were also some differences in the reliability of the solutions - Python and Tcl had a very good score compared to C, although the small sample size for C may give misleading results.
I'd personally be very interested to see better data for differences between C and C++. I've recently been involved in C again after a long pause, and it seems like an awfully risky language to program with. However, it may be faster than C++, on average, and the Prechelt's results agree with this conception.
Re:Software Schedules (Score:4, Insightful)
The thing is, you must get entirely through the design stages first. The design stages should include every screen as well as every possible error message, sub-screen, or whatever can pop up, as well as an outline of how the program flow will go. This takes a lot of time, but not quite as much as it sounds.
Once you have done the complete design, you can accurately make schedules. The problem is, most programmers put all error handling and messaging off as something that doesn't need to be designed. That's where the extra time comes in. If you know _exactly_ how the program flow is supposed to work, estimating time is easy. However, if you haven't finished the design stage, YOU DON'T KNOW WHAT YOU'RE PROGRAMMING, so, obviously, you can't estimate the time. So, with a _complete_ design, including all possible error conditions and actions to be taken, scheduling is not that hard.
Parent
Of course they can be estimated. (Score:5, Insightful)
Software development is not a science in the normal sense. Designing large software systems is an art. It cannot be pigeonholed. Stroustrup has a lot to say about this when he describes the 'interchangable morons' concept in the 2nd edition C++ book.
Anyway, read Death march by Ed Yourdon, and the mythical man month by fred brooks, and antipatterns, any time someone asks you for an estimate say 'two weeks' and then bullshit from there on.
That is how it works in the real world. The numbers are essentially meaningless, but the bean counters and suits have to justify their existance somehow :-)
Can you imagine asking Linus when 2.5 will be ready ?
Re:Of course they can be estimated. (Score:4, Insightful)
That's exactly the sort of attitude that has caused the sort of spectactular failures of software projects to be accepted as the norm. Software Engineering is *not* "hacking" or "coding" or "programming", it's *engineering*, like building a bridge or a skyscraper. Yes, those projects go over time and budget too sometimes, but they are the exception rather than the rule.
That is how it works in the real world. The numbers are essentially meaningless, but the bean counters and suits have to justify their existance somehow
The problem is endemic in the industry. The other Engineering professions require rigorous accreditation before they let practitioners loose in the world, like the PE (in the US) or the Charter (in the UK). But the software industry hires anyone, and lets them get on with whatever they do, with no real management or oversight or planning.
In a well analyzed and properly planned project, the actual coding stage is little more than data entry.
Parent
Re:Of course they can be estimated. (Score:5, Insightful)
If you're building your 57th e-commerce web site, which works roughly like the 56 you build before, you can estimate very, very well, and you can reduce coding to nearly data entry.
If you're solving a problem of unknown scope, which your team has not solved before, which the solution is not clear to, and analysis has revealed some but not all of the details, etc., then you are not very right.
Parent
Re:Of course they can be estimated. (Score:3, Interesting)
When looked at in the context of practical experience, this is quite false. We have been building buildings for at least several thousand years with some tremendous success and some spectacular failures. I live in Toronto where we were lucky (I think) enough to have the first major league baseball stadium with a retractable roof. IIRMC, the original cost estimates were in the vicinity $100 million (CND). When the stadium opened (pretty close to on time), the cost was actually around $480 million (CND).
I guess this somewhat proves you can estimate either cost or time accurately but not always both. My experience in the IT industry has shown that most problems can be over come with enough resources. Unfortunately, resources are not limitless and therefore consessions must be made. This generally means the completion date slips or functionality is reduced or a combination of both.
Re:Of course they can be estimated. (Score:5, Funny)
Parent
Re:Of course they can be estimated. (Score:5, Insightful)
That's exactly the sort of attitude that has caused the sort of spectactular failures of software projects to be accepted as the norm. Software Engineering is *not* "hacking" or "coding" or "programming", it's *engineering*, like building a bridge or a skyscraper. Yes, those projects go over time and budget too sometimes, but they are the exception rather than the rule.
"
But that's simply not true. Writing software of anything that is non-trivial is not the same as straightforward engineering. For a start there is the rate of progress, how many people have 30 years + experience of building 50 story + buildings. How many people have 30 years + experience of dealing with terabyte + sized datasets?
When buildling software previous code can be reused for a very small amount of effort, when building skyscrapers the previous design can be reused for only marginally less effort than the last one.
Compare the difference between building a C compiler from the gcc source and the world trade centre from the blueprints.
Essentially the estimate is
Time = [time to do the bits we know how to do [accurate] ] + [guess for the bits we don't know how to do [inaccurate] ]
With software, the first part of that expression tends towards zero since most things we know how to do we can reuse code, whereas with building it remains a large accurate estimate.
The error here will be of the form
Error = [variance of inaccurate terms] / [total]
For the example of a skyscraper whos construction is mostly a known method this will tend to a small number since the inaccuate term is much smaller than the accurate term, but for software with reuse of all the known methods of coding this will tend to 1 - i.e.. 100% error in the estimate and hence the conclusion that it's worthless to even bother estimating.
In my company we can accurately estimate how long projects will take providing the projects are mostly identical to ones we have done before, and if this is the case it generally costs the client more in programmer time in meetings to dicuss the cost of the job than it does to write it.
Parent
Re:Of course they can be estimated. (Score:3, Interesting)
The software industry doesn't hire anyone. Software companies hire people, and a company that behaves like you described won't be around for long if software is their main source of revenue.
Also, management != good software engineering. Planning != good software engineering. These are all factors that go into a good software project but people shouldn't think that if they draw class diagrams before they start coding, they're suddenly software engineering.
On the other hand, you need to look at what's best for the project - it isn't always a large, formal approach to software, especially for small projects. Being too rigid can be as bad as being too loose with your design. I've seen projects design themselves into a corner before the first line of code is even written.
Software Development==Engineering? (Score:3, Interesting)
I agree with you up to a point. I am an engineer. I have worked in Process Engineering, at AMEC, and now work in Design engineering. I have not done much coding, but I think that software development probably relates most closely to design. As I said, I now work in design. In design you can estimate a schedule, but that schedule is dependant on our everything going perfectly the first time, which we all know doesn't happen. This does also not include problems with parts we have to design around, which we then have to wait on, or a change in requirements of our part. (Sound familiar yet?)
This is all in the conceptual, design phase. This doesn't include the acutal production of a physical part. That all happens later, after our 3D model has been packaged correctly. Once the physical part has been made, then there are the joys of testing and testing and testing...
What I'm trying to get at, is that I've experienced several forms of Engineering (Yes there are many), and I think that Software development relates most closely to Design. In design, there is no reasonable way to schedule out how long things will take. We just make an estimate based on what's happened in the past, and change things as we go along.
Just like building a skyscraper (Score:4, Insightful)
Parent
Re:Of course they can be estimated. (Score:5, Insightful)
After ~15 years in the industry, I've found that one thing that makes a huge difference is the experience of the team, and the familiarity between the actual engineers and the project management.
As you have experience solving a variety of classes of problems, you can predict with increasing accuracy the time it'll take you to solve later problems. And as your management sees you getting increasingly accurate in your estimates (based on past projects) they can create better and better schedules and estimates for the project as a whole, and have a better intuition for the gray areas of development, or the greener developers.
Projects that tend to go off into the weeds have included (in my experience) wholly green teams, wholly green management, or areas of development that are outside the areas of expertise of one or both.
Parent
Re:Of course they can be estimated. (Score:5, Insightful)
However, the biggest thing to remember is that no matter what estimation method is used, the simple fact that a methodical approach to analyzing the problem will almost always yield a reasonable estimate.
The main reasons projects go over schedule and budget are:
Risk management is indeed the key. As the project manager or lead engineer, it is your job to predict what potential risks might be and attempt to mitigate them on a cost-effectiveness basis. You can still be bit by bad luck, but you can minize the chances it will strike.
Parent
Sure they can... (Score:3, Interesting)
And the remaining 5% of the project takes another 95% of the time.
from a Consulting viewpoint.. (Score:3, Informative)
To accuratly plan a software release you must have the project, and all it's complexities and nuances down COLD. otherwise you are not giving an estimation, you are giving a guess based upon incomplete knowledge.
The question becomes, do or, can you, know the complete details of the project? In this, software development is NOT like manufacturing, but more like home construction.
Think about it.
Re:from a Consulting viewpoint.. (Score:5, Interesting)
The bulk of the work of programming consists of getting all the complexities and nuances down cold. Once you really and completely understand what is required, coding is trivial.
This leads to a thoroughly unrealistic method of estimating software costs:
1) Work for months on the specs.
2) Get the customer to sign on to those incredibly detailed specs, even though he doesn't understand them.
3) Go and code it, no spec changes allowed.
8-)
The article mainly talks about the mathematics of estimating complexity. This is a lot like the proof that you cannot determine when or whether a computer program will end -- it's true for pathological programs, but it has little relevance for the real world. You try to write the code so the conditions for the program to end are clear. If it gets into an endless loop, you probably got a conditional expression backwards and you'll recognize it immediately once you figure out which loop is running endlessly... Likewise, there may be well-defined specifications for which it is impossible to estimate the coding time, but the usual problem is poorly-defined specs, which obviously makes any estimate a guess.
Parent
Fixing the endpoint? (Score:3, Insightful)
So the easy response is that bad management in general, and bad project management in particular, is responsible for software project failures. While this is no doubt true, the next question has to be, why do software projects have such bad project management?
I don't have a good answer, but one thing that occurs to me is the lack of a fixed endpoint. When an oil refinery ships its first load of POL, it is complete. When an aircraft carrier launches its first plane, it is complete. But the amorphous and mallable nature of software means that it is hard to define an exact endpoint, and very hard to avoid changing the definition of the endpoint as the project proceeds. So things keep "creeping" along until disaster occurs.
sPh
Re:Fixing the endpoint? (Score:3, Insightful)
Note also the enormous difference between building the first 747 / skyscaper / nuclear submarine and the 15th or 1500th of each.
Components (Score:4, Interesting)
Yes but. The important components of a skyscraper are steel beams. Put them up correctly, after calculating loads and stresses, and it doesn't matter what the twenty tons of stuff you have sitting on the 27th floor is. It doesn't matter if the beams come from different foundaries, either, because the specs are clear enough (dimensions, strength, where the bolt holes are).
Now try putting together a typically complex business software solution, meshing a bunch of different, reasonably good, existing programs and components with some custom code and configuration. Even where there are reasonably good standards spec'd in some areas of the project, if you're not solving new problems it shouldn't be a software engineering project at all - it should just be system administration using the available solutions. That it's real software engineering means you're running into unpredictable surprises where the components at hand don't fit without a great deal of extra labor.
A parallel can be found in work on the portions of the New York City infrastructure that are under the streets: We still have wooden water mains in some places from the mid-1800s, mixed with gas, electric, steam pipes, sewer, subways, gas lines ... most of which was not documented to current standards on either installation or subsequent changes, despite most of it being reasonably well done by the standards of its time (pretty amazing, those wooden water mains still working, right?).
So what happens when we finally go in to improve one of the services - say, lay new water mains? Other stuff is found that's in the way where you didn't expect it, or that need's fixing on examination when you didn't expect it. Meanwhile you've got the street ripped up but you have to cap it again quickly or traffic is too snarled for too long. So a single block's 4-week project can stretch out for over a year - dig up the street, fix one problem, discover more, recap while designing and provisioning the next stage, repeat - because it's all stuff that needs to be done once you get into it, that can't be properly assessed until you get into it.
Well, software in the real world isn't as old as New York, but if anything it's more complex, and the layers of crufty stuff that have to be accommodated in current projects are as considerable, and often as poorly documented by current standards (which will always advance so as to obsolete whatever we do now). Building a skyscraper, by contrast, is just a sysadmin job. Put the beams and bolts in the normal places, and it stands.
Parent
Incompleteness (Score:3, Funny)
Lewis also provides a link to this "introduction to incompleteness" (a fun subject in itself)
I started writing a paper about this topic once, but I never finished it.
-WetDog
Estimates based on motivation (Score:4, Insightful)
My company develops turn-key systems. Sometimes we also develop custom solutions for our customers. Our customer base has increased steadily after the dotcom crash, when we switched from products to services. One of the reasons our customers like us is that we don't bill projects by the hour. We will the project on a fixed price, not to exceed, basis.
The programmers who work with us on a contract basis don't bill us by the hour either. After we have the design and we distribute tasks and prior to submitting the final estimate, we ask contractors to place a fixed bid.
We've done six major projects like this since March, and in all cases we finished within budget and on-schedule, and the systems are currently in production. They are all mission-critical systems running in either robotics environments or high-availability networks.
Our economic motivation is then to do things well and quickly in order to increase our profits. That also enables us to move on to the next project faster than slaving over some customer in order to bill the maximum hours.
As far as development techniques go, we adopted XP earlier on and it's working for us.
Cheers!
ERe:Estimates based on motivation (Score:3, Interesting)
A key to fixed-cost is that it takes practice. Try it on a small scale before you commit to it on a larger scale, to avoid large-scale failure...
Re:Estimates based on motivation (Score:3, Insightful)
How do you reconcile this with the nature of XP projects to deliver something that is noticeably different from the customers original conception of their need (but that in fact fits very well the customers need as learned over the course of the project?)
I'm seriously interested to hear about folxs who have figured out how to marry an agile development process to fixed cost contracts.
Much more like manufacturing than physics. Mostly (Score:3, Informative)
The reason that estimates are always wrong are *1* unclear requirements, *2* changing requirements, *3* complicated user interfaces, *4* weak focus on testing.
I find *1* to be the biggest difficulty. The prinicipals of a software project like to say things like "Automate timeclock operations" but as a developer, you need *A LOT* of information to do that. When you ask questions like "I understand that you do not want to allow any changes to a pay period after the checks have been cut, but then what are we going to do when travelling workers report their hours late?" Management thinks you are being a pain in the ass, but if you don't get it right, your project will fail.
I agree with taking a realistic estimate and doubling the both the developement and the testing estimates.
There are four parameters (Score:3, Insightful)
- Quality
- Quantity
- Deadline
- Costs
In a competitive environment with humans involved, up to three can be specified. Not four. Good examples are:
- Many guidelines for managing software projects tell you to reduce quantity when you get near deadline.
- Some customers have a specified budget but really don't know how much software they can get for that money. They prefer to have costs fixed than to have quantity or deadline fixed.
- Sometimes deadline is so important, that costs may 10-double in order to reach that deadline, and quality and quantity may get reduced a lot in order to finish the project.
It is extremely important to realize the meaning of all four parameters before you can talk about estimating project schedules.
Lars.
The short answer: no (Score:3, Insightful)
The biggest problem I've seen is requirements creep. Most often, you don't have a firm set of requirements to start with. Management and programmers both have a tendancy to view requirements documents and other formal software engineering practices as superflourous. The problem is that without a firm set of fixed requirements, you are always trying to hit a moving target.
Another problem is attitude, mostly on the part of management, but programmers are guilty too. One faulty attitude is that we are conditioned to expect immediate results. There's also a prevaling attitude that there is never enough time to do it right, but there's always enough time to do it over. This leads to undocumented, unmaintainable masses of code that either gets thrown away after a while.
Even worse, you wind up with garbage code that SHOULD be thrown away and re-written from scratch, but winds up getting patched and modified for years. I can't tell you how many times I've had a manager say "there isn't time to rewrite it, just patch it". That would be OK if you are only going to patch it once -- but you wind up patching the same program a half dozen times, and it winds up taking twice as long to do all the as it would have if you had just rewritten it from scratch.
2 weeks (Score:3, Insightful)
Gung-ho programmers are optimists. Couple optimism with the ennumerable factors involved in programming a non trivial application and you will get what we have today.
By the way. I am a programmer and I have little to no confidence in my time-estimation abilities, or anyone elses. It has taken me 14 years to come to grips with that.
Software like a factory (Score:3, Interesting)
1. Discipline. Your average programmer will have read about various programming methodologies, but skipped past the parts which would make their code an easy-to-reuse template in lieu of fast development time. As with any gamble, you should know at exactly what point you want to quit, have an A-line for version 1.0's feature set, all that jazz.
2. A big code base. Because of step 1, or maybe just a lack of previous projects, one's code base is typically limited to what you can find in a computer science textbook. Having a good database of classes and patterns that have turned out to be useful, and having easy access to this database for the information you need is the difference between a library and a code base.
3. Incremental development. Throwing together a large software project, all at once, and then testing the whole thing is very tempting, and happens more often than most people like to admit. What should be happening is a series of incremental integrations into the final product, with unit tests of each part. Otherwise your large project can become a giant, complex nightmare. Making complex software shouldn't be made quite so complicated.
While making a "software assembly line" takes slightly more work and trouble than your average car assembly line, it has incredible cost savings in the long run.
Estimation is very possible. (Score:5, Insightful)
If we built homes like software we would all be living in the street, penniless...
The major issues I have seen revolve around a lack of scope and cost control. In many cases it is because there is little penalty for being late or over budget. In cases where penalties exist it is often beneficial to then over estimate the effort or cost required. Then once the money is approved, using it is becomes easy.
Going back to the analogy consider the following:
Scope
If you were building a house, each piece has a specified cost, known in advance to a very large degree. In addition, altering the scope itself often incurs a penalty, because the work is not done by the owner. You plan a three bedroom, 1.5 bath home. Midway through planning you decide to make it a two bath home instead. The architect will charge the "re-scoping" fee and the builder will add the material fee. Now do the same after construction has begun. The architect gets their fee, the builder adds the material and resource costs, plus a "revision" fee for changing your mind after construction begins.
During a software project, it is common for individuals to approach the developers and ask to expand the scope. This would be analogous to approaching one of the work crew and asking them to just add the extra half a bath. The difference is the work crew would get fired, and the developer gets bonus points for adding the feature, either directly or indirectly.
If the developer chooses not to do it, or pushes them to the project manager, the client may label them uncooperative or difficult to work with. The project manager not wanting to be labeled either may coerce, cajole, or beg the developer to accomplish it, without a scope revision. Failure to do so by the developer results in real financial impact at some point, and offers little incentive to hold the line.
Cost
I call this the "Porsche syndrome".
I go into the Porsche dealership and see a new 911 Carrera Coupe. Smiling the dealer offers to sell it at a deep discount, with options and accessories $84,000 (U.S.). Whewwww baby!!! I cannot afford that. "Look," I tell him, "my wife will never approve that, you need to get it down to $28,500 tops." Would any of us expect to have the price cut down? By half or more?
Okay, how about "Look, what will it take to get it under $30,000? Seriously now, what do I have to give up" As the dealer is escorting me to the door he explains the only way I will get this car under $30k is with a mask and a gun or from a scrap metal dealer.
Yet, daily we go to developers and tell them to do the same. We ask for an estimate and then go back with "This is too much, it needs to be smaller or it won't get approved!" --Insert blank stare here--- The idea that if something cannot be cost justified it should not be done, is often lost in the "request" itself.
To nearly guarantee a project is on budget and time requires things many companies are unwilling to provide. Strict scope control procedures, with oversight by the person responsible for the money. That means each change, regardless of how trivial must be approved by someone above the project management team with business justification. It also means that requests for scope change cannot be made to developers directly, by anyone.
I was very happy with the people who built my home. When speaking to many of my friends and coworkers who built their homes, they describe it as a process akin to having their flesh removed. Everything required such effort and detail that many would not do it again.
Most of them were looking for the relationship to be like one at the office. We all want to get along and help each other out. This is not a commercial arrangement, and when we put the commercial context around it, we see it many offices lack structure.
Internal organizations can be setup like commercial ones, but it is usually unwelcome as the perception is everyone should be working for the greater good of the company and this has the appearance of bureaucracy. Even if inaccurate, everyone "wanting to get along" prevents it from being implemented.
Software can be scheduled... (Score:4, Interesting)
Painless Software Schedules [joelonsoftware.com] is a great one and you will get sucked in just following the links from this one essay.
Reductio (Score:3, Interesting)
Next get together a team of programmers. Set them to work on a program which determines proves {insert your favorite unsolved mathematical conjecture here}. It turns out you actually don't need the team at all, just run your software project estimator and if it comes out with a finite amount of time to complete the program, you know that the the conjecture is true.
In other words your software estimator can be used to solve the halting problem.
OK, this is a joke, but it points something about the question. I once had a CS professor who required that we right requirements statements for all of our assignments. She forbade us to include halting times, because "you can't predict whether a program will halt or not." To which I wanted to reply, "About that 'hello
The lesson is that there are some cases to which a rule like this applies and others to which it does not. There are some projects that can be estimated with simple tools, some that can estimated with complex tools, and some that are not practical to estimate at all. Even fairly seat of the pants kinds of estimates work pretty well on relatively simple problems, providing you break things down a bit and do an honest estimate the costs on individual deliverables and the individual functions you know you'll need to make them work. About the only methods that never work are pulling a number out of the air based on how much the project scares you, or using wishful thinking (whether the source is your boss or you). Nobody can give good estimates when you spring the question on them with no time to prepare. My boss's most (and my least favorite) questions start with "how hard would it be.." and my most favorite (and his least favorite) answers start with "It depends..."
Nonetheless, my experience with past projects of the kind that I do means I can do a pretty good job with relatively unscientific tools, provided the problem is like one I've solved before. However if you are writing software for space flight or some other kind of highly complex mission, I could estimate until I was blue in the face and it wouldn't be worth a damn. You want to hire somebody with experience in such projects and who has methods of estimation well calibrated from similar past projects.
I think the particularly difficult cases are ones inolving software maintenance -- extending software to perform things that weren't originally factored into the design, or adapting the software to run when the systems it depends upon change in some unpredictable way. These are cases where surprises can throw the best laid estimates well off.
Estimates should include debugging (Score:3, Interesting)
* A tester or test suite exhibiting the bug
* Someone recognizing that it is a bug
* Enough data being gathered to define the bug ("It hangs sometimes" or "I don't think the results are always correct" doesn't cut it).
* Enough eyeball hours to find the bug (this in itself makes the process equivalent to solving a crime. Do we ask the cops to schedule crime solving?)
* About two minutes (average) to devise and implement a fix
This has to be done for N bugs, where N is unknown. People who think you can estimate software development schedules with any accuracy are either dreaming or assuming that they just have to estimate how long it will take to get it coded, not how long it will take to get it working correctly.
-- MarkusQ
The problem with software development. (Score:3, Insightful)
The customer claimed it was because I could not seem to fully complete a component of the project. What they really meant was I could not fully complete a component of the project before they would request a change to that component that in some cases required a complete rewrite of the component. They didn't think it was a big deal to add a button here or there in the application after all it was only a button. Never mind the fact that each of those buttons required stored procedures to be written and existing stored procedures to be altered. They would get upset that I could not make their requested changes in a day when they wanted to completely alter the way the interface to the application worked.
The bottom line is most people who don't know anything about software development don't think it is a big deal to add a feature here and there at the end of the development cycle. I try to equate software development to carpentry. Sure I can add another door in the center of those cabinets, but don't expect it not to affect the other doors and their space within.
Not just experience counts, so does Humility (Score:3, Insightful)
Personally for me, I tend to do the best hourly breakdown I can and then double it before submission. This is normally not too far wrong (say one week on a 3 month project). The double factor allows for inaccuracies, meetings (which really do take time !), and spec changes. I may add more "fudge factor" depending on my feelings for how well the spec is sorted out and the quality of management (i.e. weak management will allow spec changes every week, good management will filter well).
ANdy
More mundane reasons for underestimations (Score:5, Insightful)
Underestimation as a Marketing Tactic
AKA "Vaporware". Even if marketing knew when a product would be shippable, a particularly cinical marketing department may claim it to be earlier, thus freezing competitor's development.
Lack of Feedback (Moving Targets)
Software engineers are particularly bad at estimating because they have never done what they estimated. They are given a large project, give a large estimate, start working on it, and the project changes in the middle in a major way. This is a moving target; the estimate no longer applies. Major law of software development: You cannot change the spec or the development team on the project without impacting the real ship date. If you don't re-assess the estimated ship date, you are simply fooling yourself. Thus, they don't have any clue whether they hit the estimate or not. One way to defend against this is to break the project down into bite-sized pieces and estimate them; a small piece gives you a chance to do precisely what you estimated. Once you have that, you can have somebody track your estimates, and come back saying something like "On average, you go one third over your estimates. Add a third to your estimates from now on, and we'll be accurate".
Management Estimates
Often, engineers don't do the estimate. The management or marketing people tell you what must be done, and how long you have. Sometimes this is done explicitly; other times, management may have a number in mind and shame a software team into agreeing with it by laughing off any number that doesn't match theirs. Business people often negotiate the ship date with the geeks, like any negotiate with any other vendor. To a suit, vendor negotiations are how you determine the "margin", or how much the vendor is making (like when you buy a car, you and the dealer come to a number that determines the dealer's margin). This doesn't work in in-house software develoment because geeks hold back precious little "slack" or "margin" (they don't get paid profits, they get paid salaries); in a decent shop, geeks program at flank speed all the time and always give the project 100%.
See Ed Yourdon's Death March or any of Ward Cunningham's Extreme Programming books for more details, and ways to avoid the above traps. Yourdon suggests that the head geek has to take a hard stand in scheduling to prevent business interests from setting both the project spec and the ship date. He especially tells you never to negotiate schedule, and to help the suits understand why you never do. Whatever number you estimate doesn't affect the actual ship date, so playing with that number is simply fooling yourself.
Extreme Programming actually has a "planning game" (sort of a ritual dance) which places business interests and geeks on the same side of the table. Two big rules are "The geeks may not reject any part of the spec" and "The suits may not reject any part of the estimate". Once the suits set the spec, both teams break it down into pieces-parts, line them up in order of what gets done first and the geeks give their estimates. From there, the suits can choose the ship date (and can instantly see how much product will be ready by then), or can choose a certain amount of project completion (and can instantly see the ship date). The fun part about this method is that the suits can change their minds at any time by changing, adding, or removing pieces-parts, and can instantly see how that affects the ship date. The other fun part is that breaking up the project into pieces-parts allows developers to do a (small) project they estimated. This allows people to track estimated versus real time, and to give developers feedback that lets them make better estimates. Such a team will start off with bad estimates like everybody else, but they will be able to improve rapidly.
Several points to be raised -- is it all academic? (Score:4, Interesting)
But herein lies the rub -- exactly how many software systems are "completely new?"
Damn few!!
The average software project in an average industry will be primarily a repackaging of previously solved problems.The majority of integration tasks will be sufficiently similar to previous integration tasks as to be known.
You will be left with a small number of "sub problems" which are unique and new. But now we have a situation where the caveats of the article are very important. Specifically, if we have decomposed the programming tasks to a sufficient degree, it should be the case that the estimation is tractable.
Also, it should be noted, that the author assumes that a good estimate is one obtained through formal methods that is objectively defensible. However, in project maangement, a good estimate is defined as one that is believable and acceptable to all stakeholders in the process. The method for obtaining the estimate is not important.
Moreover, good project management will include some significant up-front analysis. One common (at least common to companies with good PM'ing track records) is to run "monte-carlo" simulations of project work with large variances in schedule-v-actual work. With a run of a few thousand simulations, those processes that are most important to the time and budget performance of the project.
These "key" work packages are often non-obvious without this type of simulation work. However, with a good work breakdown structure and a good simulator, it is possible to generate a reasonably accurate picture of project performance based on what is not known.
This means that in the "real world" of business, the article's claim is irrelevant!!
We don't NEED objectively defined and defensible estimates. Instead we need estimates that the project stakeholders (which includes the people doing the work) can agree to.
We don't NEED our estimates to be generated by formal methodologies. Subjective estimates backed up by years of experience are just as good, and often better, from a planning perspective.
This whole article strikes me as another programmer trying to show how dumb the business people are. Hey folks, good business people KNOW that estimating is hard and that it isn't objective. But just because something isn't objective doesn't mean it can't be done well. It is possible to build models that compensate for unknowns if you can do enough decompossing of the problem to limit the unknowns to a well defined, small manageable few.
So, in the view of this PM, this is all just academic and has no bearing on the real world.
Why almost all the posts are off topic. (Score:4, Insightful)
Standard estimate (Score:4, Funny)
comment on the posts (Score:4, Insightful)
It looks like several people (well, more than several) posted responses without reading beyond the lead-in. If you're one of them, yes, the argument here is in the general ballpark of "software estimation is hard or impossible", but it actually says something more specific than that.
The article does NOT say the following:
The article DOES say
From this, it does NOT conclude either of the points 1,2 above. Instead, it concludes:
Now some of the response posts, paraphrased:
No, it does not say this.
It also does not say this.
No, the article distinguishes subjective and objective estimates, and specifically discusses the case of an objective estimate with bounds in detail.
Ok, but slightly off topic: the article is specifically talking about those who claim objective estimates.
And where did you get an objective estimate of the complexity of a new project? Read the article...
Yes, you are. Your boss is monitoring you, get back to work.
Certainly. The 'manufacturing' camp of software estimators (Humphrey quote in the supplementary material [idiom.com]) say or hint that software construction can be made into a repeatable, fairly boring process where projects are always on time and programmers are like factory workers. This may or may not be true (I don't think it is), but regardless: to make this view seem more science than philosophy some of these people have fallen into the trap of cloaking their estimating process with formal notation and claiming or hinting objectivity. This part is wrong.
On the contrary, [conclusions to the article and the supplementary material]:
Re:Double the number, add one and raise the unit! (Score:4, Funny)
Parent
Slashdot readers are students? (Score:3, Interesting)
i've always thought most
-c
Re:Slashdot readers are students? (Score:3, Funny)
Re:In all seriousness, this is the wrong place to (Score:5, Informative)
Fixed specs are much easier to engineer than those that continually change. You wouldn't easily engineer a bridge if the river banks kept moving.
I think experienced project managers know how to control the spec rather than the project. (I could be wrong - It's just what I've seen).
Parent
Re:In all seriousness, this is the wrong place to (Score:4, Interesting)
Parent
Actually.... (Score:3, Funny)
Slashdot Reader != Slashdot Poster (Score:3, Interesting)
That aside, my experience in software development (only 3 years) ball parking (1-3 days, 1 week-3 weeks, 1 month-3months) is usually possible, but tends to become wildly inaccurate beyond a few months. Regardless of what methond we use to determine timelines, some things always seem to slip, while others take a fraction of the expected time.
Re:Right place to Ask (Score:3, Insightful)
Likewise, I've been developing (C++) for a living for about 12 years now and I've come to some conclusions:
There are estimating techniques/metrics which will work. They depend upon going round a few times to "calibrate" and consistent application. "Task Points" was a good one - basically break your use cases down and down until you have a series of one-line statements about the system. Multiply these by your magic number and that's the estimate. This, like all estimating techniques, is built on sand because:
It depends upon a development team sticking around long enough to do a few projects to calibrate you method.
It depends upon the exact functions of the system being known at the time you do the estimate. This is the killer.
I have never worked on a project where the exact functioning is known at the time coding starts. I have, however, observed that the more analysis/design you do before estimating, the more accurate the estimate is. The problem is, that people always want the answer (estimate) before they've given you the problem (spec).
FWIW On small projects (which are generally better defined), I run through the spec, do a rough n' ready count up of the number of classes, multiply by a factor (decided by the complexity of each class and who I think is going to code it) add a QA+debugging allowance and come up with figures which aren't too wide of the mark.
Oh yeah, and the "who's coding it" is important. Lots of studies show that the difference between "good" and "bad" coders can be a factor of ten. I've been slammed by PMs after estimating how long something would take me, then the PM puts some "cross trained" ex VB dork on it.
To summarise: it is possible if you know who is coding what. Recommendations: 1) read Brooks, 2) keep it small 3) ignore any of the "latest methodologies" that Project Managers try and sell you.
Re:Be afraid of the unknown (Score:3, Insightful)
Figure the time to do the parts I understand.
Count the parts I don't understand. Allow a very long time for each of them.
Add it all up, then multiply by 3
When constants are constant and when they aren't (Score:3, Interesting)
There is nothing wrong in principle with measuring what has happened in the past, and using that to predict what will happen in the future, before you discover why it works like that.
For instance, if you measure that throughout the year, the average time between sunrises is 24 hours. You can use that number even though the only explanation for it that you might have is "it seems to work"
Of course, when you apply this to software develpment time estimation, it falls down for a number of reasons. It's not constant across technologies. It's not constant across types of project. It doesn't take into account the variation in technological risks (ie if you have done something like this before, you will spend less time finding ways to do stuff). It doesn't scale linearly with the size of the project. It varies across individuals. etc. etc.