On 8 October 2010 21:58, Marnen Laibow-Koser <[email protected]> wrote: > Colin Law wrote: >> On 8 October 2010 18:21, Marnen Laibow-Koser <[email protected]> >> wrote: >>>>> else. >>> is, everything that is actually of value to the user. �The user never >>> sees or cares about the internal workings of the application (except as >>> specified in his requirements); they are not of value to him. �Only the >>> functionality is of value to the user. >> >> I don't entirely agree here. Firstly the scenarios only describe the >> functionality of the current phase of development. > > Which, at any given time, is all we care about.
My turn to say No! I agree that one should not do extra work to add features that may never be required, but where choices exist that do not add extra work then the design should be so as to provide the best base for future extension and modification. > >> The user has an >> interest in the internal workings of the application in so far as he >> expects there to be further phases and therefore expects the design to >> facilitate later phases as far as possible, even though he may have >> little idea what those phases may be. > > No. The user wants the application to work. Other things being equal, > he doesn't care how. The internal workings are irrelevant to the user; > the concern of further phases is one of project management, not > internals. > > It's to the *developer's* advantage to structure the application so that > adding more value for the user will be as easy as possible -- hence good > development practices -- but the user sees and cares about none of this. > > Don't kid yourself that the user has any reason to care about what goes > on under the hood, as long as the application works as specified. My experience does not match this. Most of my work has been in-house developments where the customer and myself are the same company. In my case management has been keen to ensure that the code base should be well designed in order to minimise future costs. Perhaps in the case of contract work things are different. I find it surprising though that a customer would not be at all interested in this. Perhaps I should not be surprised however. > >> I know we don't want to do >> premature optimisation however, I will come back to this below. >> >>> >>> Now, since only the functionality is of value to the user, from that >>> perspective it is clear that the only purpose of the application code is >>> to provide an implementation that delivers that functionality. �If we do >>> anything else, we are not providing any particular value to the user. >> >> Again I will quibble, slightly tongue in cheek, though not entirely. >> The purpose of the code is to provide the implementation, as you >> state, however the process of developing the application has other >> purposes. Notably to provide us with a living wage and job >> satisfaction. > > That adds value for the *developer*, not for the *user*. If all we care > about is running up the billable hours, there are lots of ways to do > that -- and not all of them involve adding value for the user -- and > soon the user will realize this and find a developer who can actually > add value for him. Oh no, you completely misunderstand me, I was not suggesting in any way 'running up billable hours'. I entirely agree that any such practice is to be deprecated. That is not in the Rails sense where it means it is ok to keep doing it for the moment but it should be phased out when convenient. :) > > Your user's goals are not your goals. > To a great extent I think you are wrong here. At first sight you might say that my principle goals are to make a living and achieve job satisfaction. However the best way to achieve that is to provide the best product to the user with the minimum effort (always a compromise of course) and hence minimum cost. The Users goal is to receive the best product for the minimum cost. Hence the goals are pretty much the same. >> I believe that to some extent software development can >> be an art as well as an engineering operation. > > Completely agreed. (My background is in musical composition, so I > *would* say that. :) ) > >> Consider initially >> just small sections of code. Often there are numerous ways of coding >> a piece of functionality, with no difference in the result of running >> the code. Usually one of these 'feels' right. Nothing in the >> scenarios suggests one or the other but we code it the 'right' way >> because we get satisfaction sitting back and savoring the design. > > Right. If we are good developers, we probably have a sense of the best > way to write something at the moment. Other things being equal, there's > nothing wrong with that. > >> OK, >> I am getting a bit carried away here but I am sure you know what I >> mean. In addition we may code it a particular way because we believe >> it will be easier to maintain > > To a point. But not much. Do The Simplest Thing That Could Possibly > Work is an important principle. Consider, for example, text formatting. If I want a bit of text highlighted the STTCPW would be to use <b> tags. It is more complex to use css. So why do we use CSS? The scenarios do not require it, but we know that it will be easier to maintain. Similary DRY is often not the simplest way to do something. It is simpler to cut and paste a bit of code rather than extracting it into a method. The same could be said, I think, about Unobtrusive Javascript. These are all design concepts that are intended to improve flexibility of the code, reduce bugs, make the app more easy to understand and maintain and so on. > Don't bend over backwards to > generalize; let the generalizations emerge. Agreed, but there is nothing wrong with standing up and looking around to check there is not a better solution nearby. > >> and is less likely to have unnoticed >> bugs. > > That's what tests are for. Hmm, did you really mean that? Tests cannot ever cover every possibility, some bugs will get through. Coding so as to minimise the likelihood of bugs is worthwhile. Also, even if the tests do point out a bug, we have still wasted effort fixing it which would have been saved if we had not introduced the bug in the first place. > >> I think these ideas also apply to the larger scale design of >> the app, including the models and relationships. The overall design >> can be aesthetically pleasing, or even a thing of beauty (I know, OTT >> again, sorry). The scenarios do not address that aspect of the >> design, only the designer can do that. > > And the user will not care one iota about all that beauty. It, in and > of itself, adds no value for him at all. No, but it increases my job satisfaction, and if it does not cost the customer anything then everyone is happy. > > The only thing adding value for the user here is that the beautiful code > *makes the app easier to maintain* -- that is, to extend functionality > -- that is, to do things that *do* add value for the user. > > To reiterate: there is no user value at all in elegant code, except > insofar as the elegance makes future development easier. There is > developer value, but no user value. The fact that the elegance makes future development easier _is_ of value to the user as it will keep his future costs down. He may, or may not, appreciate this but it is still true. It also adds value for me as it will assist me in meeting future targets (in the in-house case) or allow tendering at a lower cost (or higher profit) in the contract case. > >> [...] >> The purpose of the models is obviously to satisfy the scenarios, but >> the purpose of the design is also to facilitate further phases, > > No! The purpose of the design is to make the project *as we know it > now* work. Further phases can take care of themselves when they come. > >> even >> though we do not know what they will be (see later again) and to give >> us satisfaction in the design as discussed above. > > Since we don't know what the further phases will be, we can't design for > them. Period. You're deluding yourself into premature generalization, > and apparently somehow think that your clients care what the source code > looks like. I am not talking about generalisation, but basing the model identification on those aspects of the problem domain that are least likely to change. That is not a more general solution than purely looking at the details of the scenarios and coming up with a set of models that solves the problem but may not be based on those aspects of the problem domain that is least likely to change. Though I suspect that 90% of the time there will be little difference between the two approaches. > >> >>> and refactor later as necessary. �Remember YAGNI. >> I am not suggesting adding extra functionality that may or may not be >> required, but ensuring that the initial design provides a base that is >> most likely to allow extra functionality to be added without major >> re-structuring of the design. > > That would require too much guesswork. There is no point in doing that > -- you'll probably guess wrong. Implement today's requirements today, > and refactor for tomorrow's requirements when you know what they are. It is not gueswork, just a matter of mapping the problem domain objects (where appropriate) to the models. > >> >>>> identify the underlying objects in that real world without worrying >>>> too much about the _details_ of the scenarios. >>> >>> Precisely. �That's what I meant by business domain objects in my earlier >>> post. �If we want the user to be able to purchase products, we know we >>> have "user" and "product" as business domain objects. �We don't know >>> (though we might strongly suspect) that we will have User and Product >>> classes in our program. >> >> I think now our ideas are starting to diverge. My initial assumption >> would be that there _will_ be user and product classes _because_ they >> are domain objects (unless the scenarios show that they do not >> actually exist in the app). > > That would be my initial assumption as well when I start to implement, > but that's because I follow such a programming style in general. > Apparently not everybody does. I am not sure what we are arguing about then, we appear to be in complete agreement. :) > > [...] >>> This is an implementation detail, and as such >>> it is irrelevant right up till the moment we start implementing. >> >> I am not sure what you mean here. > > I mean that the nature our object model should be of no concern to us at > all till the moment we start to write actual code. Surely you have a phase where you sit back and consider the models and their relationships before you start typing? > [...] >>> >>>> �Scenarios will be modified and added >>>> to dramatically over time but the underlying objects in the >>>> requirements are less likely to change (I don't mean that their >>>> behaviour will not change, but their existence). >>> >>> That's true with regard to the underlying domain objects. �It is not >>> necessarily true with regard to the underlying program objects. >> >> But that is the point, if the domain objects and program objects map >> onto each other closely, > > Which there is no guarantee that they will. I believe that they should. > (There was an interesting > post from Jim Coplien a while back where he said that very few bank > systems actually have any sort of Account object internally, even though > there's a business concept of an account.) I can't seem to find that. Assuming it is correct I wonder why that is. It would certainly not be my starting point. In addition just because it is true does not mean that it is ideal. Are banking systems renowned for their good design or are they a hotchpotch of legacy systems lashed together over the decades to more or less work? > >> then since the domain objects tend not to >> change dramatically the program objects will also not change >> dramatically (though their behaviour will be added to and modified of >> course. > > Behavior is most of what program objects are about. That's not really > true of domain objects. I guess -- and I hadn't realized this before -- > that in that sense, the two are somewhat incommensurable. Can you give examples of this? I am not sure what you mean. > Perhaps this > is why some OO experts don't like modeling domain objects with program > objects. I wonder. > >> >>> >>>> �If the >>>> identification of the objects is correct (or optimum or whatever) at >>>> the start then this will minimise the effort in tracking the changing >>>> requirements. >>> >>> But that's not even true. �It assumes a degree of clairvoyance regarding >>> the future directions the project will take that we do not generally >>> possess. >> >> Again, by mapping domain objects closely to program objects then >> clairvoyance is not required as domain objects tend to be stable. > > Really? What happens when your client's business model changes? I did not say they never change, only that they tend to be stable. Plus I am only talking about domain objects that appear in the problem domain. If these change then I would expect the scenarios to change. Or > when you discover domain objects your client didn't know existed? (Not > so far-fetched; see http://c2.com/cgi/wiki?WhatIsAnAdvancer for a > real-world example.) That is not a problem, it is immaterial who identifies the existence of the objects. Colin -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
