The Facade pattern puts up a new interface — that is, a facade — in front of the original system. In this sample book chapter, you’ll learn when to apply it, and how to do so. Elsewhere, this chapter provides an overview of Unified Modeling Language (UML), a graphical language for modeling businesses, software applications, and system architectures.
Understanding The Facade Pattern; Introduction to the UML
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Eugenia Loli
Ex-programmer, ex-editor in chief at OSNews.com, now a visual artist/filmmaker.
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In their day to day work. How many people use UML?
I for one. I do a lot of web development work (back-end mostly) in a team of five (sometimes seven) and using UML is _the best_ way to keep everyone talking the same language and agreeing upon how to approach problems with an eye for consistency and easy-understanding for future developers.
Though I intend to keep this job for a while. 🙂
For another view of this pattern than this and that one in the GoF book I recommend reading about it in “Pattern-oriented software architecture volume 2”.
GoF is more of a reference. I’m going to take a look at what meng recommended and I’ll recommend “Design Patterns Explained: A New Perspective on Object Oriented Design”
The facade pattern is one of the easier patterns to wrap your head around. Sometimes it’s hard for me to wrap my head around some of the other patterns because it’s hard to see the patterns in code (and as I mentioned before, the GoF book is more of a reference and not very good at explaining patterns).
But in some C# code that I’ve been working on today, I’ve been using factories, singletons, and programming to the interface, not the implementation.
Hi,
Are there any UML alternatives?
How exactly do you use UML for webprogramming, I don’t understand how it can model an application that is made out of pages, frames, links, forms and such? Or do you use some kind of extension?
I only know about WebML that is a modelling language specifically for webpages.
A lot of “design patterns” only exist because of limitations in the programming language being used. For example, “visitor” makes up for the lack of multiple dispatch; when programming something like Common Lisp or Slate, you simply define some multimethods and the ‘visiting’ becomes trivial method calls. Also, “singleton” is, depending on how you look at it, either a global variable, or an oddball object in a prototype-based object system. “Facade”, “delegate” and similar “patterns” are again made redundant by delegation support in the object system. There are many more examples of “design patterns” made redundant by closures, reflection, and so on.
Just like a C programmer will develop “design patterns” to simulate the lack of basic OOP, a Java or C# programmer will develop “design patterns” to simulate the lack of advanced functional and OOP features.
In the same way that like writing OOP code in an OOP language like Java or C# is nicer than simulating OOP procedurally in C, using a powerful dynamic language is nicer than simulating these advanced features in Java and C# “design patterns”.
I believe “design patterns” amount to nothing more than code duplication, poor understanding of the problem domain, and poor choice of tools. While for typical corporate IT this is okay, anybody doing development of advanced code should seriously consider ditching the 70’s-style Java and C#, and try a language that fits the problem domain, without requiring clumsy duplication of these “design patterns”.
Design patterns, laugh a minute!
Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use.
Intent: A unified, high-level interface
Abstraction! Wow, what an amazing idea, I would never had thought of that!
Lisp, Slate and whatever oddball language you want to throw in there is obviously not the panacea to all the software ills out there or we would be using them….no matter what smug lisp weenies think. Obviously dynamic languages are the wave of the future but Lisp, its derivatives, and these other dynamic languages have performance problems and quirks.
Now you can make yourself feel better by toying around with “advanced code” (that’s funny) and claiming that “if only we had all been using Lisp all this time…” but the rest of us need to get real work done and not play around with toy-derivates/flavor-of-the-week lisp.
In my personal experience, i have found that for a very skilled programmer, most of UML just gets in the way.
My partners and I are used to creating very complex, over 100k LOC apps all the time, we dont really use “UML” per se, but have a lot more efficient approaches for teamwork.
We have our own philosophy that we developed after more than a decade of working together. Basically our most important rules when writing a project is.
-Make diagrams, use cases, etc only when necesary.. dont just do anything because thats what they taught you.. in my case, interfaces, control/data paths and storage usually make the most sense to me, but the rest of them (flowcharts, context, states, etc) are pointless.
-Define all the internal areas the project will have and separate them properly
-Write EASY TO USE interfaces for EVERYTHING, even if that requieres more code.
-We make a very clear distintion of what is a data container and a data processor and always make separate objects for that, we never make objects with the function of both containing AND processing data.
-If an object is too big, we split it in parts
-So you get it basically, we just avoid large and messy stuff and rather have small but specific stuff.
-Prioritize EASE OF USE over FLEXIBILITY
-Dont think on how to make something flexible unless necesary
-Never say “I’ll add this just in case we need it” we never add something to an object unless it’s actually needed
-We agree on a coding style
-We are not sissy girls that dont want to touch anyone else’s code and we got used to reading each others code and changing it if needed, to the point we just dont make mistakes or break things.
-And so many more things, I guess i should write an article..
And probably a lot more things.. the result is very organized and readable code that does just what one would expect, and not something super flexible that can do everything addapted to something in particular. Just accept it.. it’s easier than copy and modify for a future/different project than have the end-of-all-reusable-everything. Programmers seem to have this idea in their heads that the more flexible the code is, the better, because it will be more reusable, but forget that making something reusable may takes a more work at design stage, than just not reusing it at implementation stage..
Ah well.. this is why i dislike all this UML-as-end-of-all-anything philosphy that i see mostly in universities.. I’m sure it is useful in some cases, but it’s by far not the ultimate solution in software design.
You have to bear in mind that your experiences while valuable, are only applicable to a limited subset of circumstances. If you are your co-workers are highly skilled and aware of each other’s skills through several years of experience then you are in a good position to work together. Many projects, especially within large IT departments (banks and the like) are being collaborated upon by people who have not worked together before and are unable to make the commitment to teamwork that you have. In addition if it is possible that some workers are going to leave the project at certain points in time then your concept of a team based solution is not applicable. UML is useful in certain circumstances. So I would agree with your conclusion that it is not a be and end all solution, but would suggest that you appear to be in a lucky situation not to have to use it due to your circumstances.
Richard
Lisp, Slate and whatever oddball language you want to throw in there is obviously not the panacea to all the software ills out there or we would be using them…
Slava didn’t say they were panacea. He pointed out that they render design patterns unnecessary, because the language either includes a feature that replaces them, or macros allow patterns to be packaged up as libraries of code. As mainstream languages adopt more and more Lisp features, its only a matter of time until most programmers learn to think about design patterns the way Lisp programmers do.
Personally, I prefer the more old-fashioned things — sequence diagrams and design documents written in prose. I’ve never seen the point of making a diagram of a class hierarchy — that’s pretty obvious from the header files. A well-written design document, to me, is far easier to follow, and allows a much richer description of what the code is really doing.
I was wondering when you were going to make a post after “smelling” Lisp in the thread.
As mainstream languages adopt more and more Lisp features, its only a matter of time until most programmers learn to think about design patterns the way Lisp programmers do.
You mean once Lisp gets a decent syntax, gets rid of performance problems, gets decent bindings to toolkits, and huge repositories of libraries that traditional static languages enjoy. Then maybe us down in the trenches can start using them. I’d love to do a lot of programming in Lua, but it’s just not going to scale.
Mike nicely asked John C.:
How exactly do you use UML for webprogramming, I don’t understand how it can model an application that is made out of pages, frames, links, forms and such? Or do you use some kind of extension?
Then John C. replied:
I am sick of these so-called ‘non-literate’ programmers, bothering me with these silly questions.
Buy a book and learn it Mike, if you can’t read then I cannot help you.
I think that was rude. All Mike did was ask a question.
You mean once Lisp gets a decent syntax, gets rid of performance problems, gets decent bindings to toolkits, and huge repositories of libraries that traditional static languages enjoy.
That’s not really what I’m talking about. Programming languages are moving more and more to using the Lisp machine model. Lisp has long used features like lambdas, multimethods, a meta-object protocol, and macros. Well, anymymous functions, aspect-oriented programming, and domain-specific language extensions are coming into the mainstream, and are very similar to these existing Lisp features. As a result, even if a programmer doesn’t use Lisp, a lot of the knowledge and principles that people apply to Lisp know will be applicable to future versions of Java, C#, and C++.
> By John Cunningham (IP: —.ourhostingserver.com)
It wasn’t me that wrote this. Please, will someone moderate it down so nobody thinks my first appearance on this forum is a rude one? *sigh*
> How exactly do you use UML for webprogramming
PHP mostly these days, using Objects and Functions mapped from charts that we draw up in ArgoUML. The advantage of everyone speaking UML in thw group is that when we need to discuss certain bits of code, it’s far easier to refer to them as “a decorator for xx” rather than “this object will be used to add more functionality to that object”.
I completely agree about this, it has been my experience too. UML, Design Patterns and all that are a great way for communicating with others and I am glad to have learnt them. What I mean is that in most university areas they teach you that if you dont apply them and completely rely on them you will become unproductive. That is mainly what I discuss, that they are not the ultimate software design approach, in regards to productivity.
I mean, it’s ok to criticize lisp cause you are frightened by parenthesis, but I don’t really think common lisp implementation suche as Allegro or CMUCL suffer from performance problems..
Lumbergh wrote:
I’ll recommend “Design Patterns Explained: A New Perspective on Object Oriented Design”
I’ll second it, it’s not so much about design patterns as an entire approach to software design.
there’s always Booch!
That is mainly what I discuss, that they are not the ultimate software design approach, in regards to productivity.
While I agree with you, if used correctly, UML and patterns, heck a defined software process, will be more productive and sustainable then a “here’s-our-final-goal-lets-start-coding” approach. Any project over, say 10,000 lines of code, be hard pressed to succeed (within budget and time) without a clearly defined process (and probably some good metrics to predict budget and time).
janeiro, I’ve got Booch’s OOAD book on my shelf right now looking longingly at me. What I think would be really useful (to me anyway) would be a UML/Patterns book with actual real example code in it (preferably Python
. Guess I’ll just try Booch for now since I already know a good amount of C++ (and since it contains example code).
John C. — sorry, I failed to notice the different IP’s before complaining about your impersonator’s rudeness. I tried posting this comment last night on FC3’s Firefox but it vaporized itself when I hit the Preview button.
Lisp has a bad syntax and nobody is afraid of parantheses (please explain to me how someone can be afraid of parantheses).
Here’s some benchmarks using CMUCL from an impeccable source. http://www.norvig.com/python-lisp.html. So compared to Python it might be quick, but it’s still slow compared to C/C++. And then couple that with bindings/library problems, deployment problems, a horrible syntax, a factionalized community (how many lisp derivatives/spinoffs are there) as well as other problems and you know why Lisp hasn’t taken off.
Lisp is nice as a research platform, but it’s academic nature isn’t really suitable for a wide variety of programming tasks.
Lisp has a bad syntax and nobody is afraid of parantheses (please explain to me how someone can be afraid of parantheses).
Some people don’t like peeling onions.
Lisp is nice as a research platform, but it’s academic nature isn’t really suitable for a wide variety of programming tasks.
I take objection to that. Lisp is disliked because people are lazy and can’t be bothered to learn its way of thinking things. Why is C/anything algol-like popular? Beacuse it really has nothing to learn: function calls, numbers, operators, ifs and elses. Go try to explain people the beauty of #ifTrue:ifFalse, and they’ll stare at you cross eyed. This kind of lazyness is not permitted in other realms. That’s like an artist making do mixing 50 premade colors to get something almost like what they wantd instead of mixing his own pigments.
Um, that site shows that Lisp is twice as fast as Java
In my experience, the GCLS isn’t a very reliable set of benchmarks. The datasets are too small to yield reliable timing, and the tests themselves are artificial.
Apart from their technical merits, if the sample chapter is indicative of the rest of the book, I’ll pass. That article is painful on the mind.
Once, I worked as a contractor for a large engineering and manufacturing company. My first day on the job, the technical lead of the project was not in. Now, this client did not want to pay me by the hour and not have anything for me to do. They wanted me to be doing something, even if it was not useful! Haven’t you had days like this?
Now read that 10 tens really fast. Haven’t you wanted to strangle the authors yet? I do.
How about?
To illustrate, I once contracted for an engineering firm where on the first day I was confronted with both the technical project lead being absent and the client requesting me to work on anything, regardless of whether it was useful or not–they didn’t like paying by the hour for nothing. Haven’t we all had days like this?
I’ve never seen the point of making a diagram of a class hierarchy — that’s pretty obvious from the header files.
Well, it helps greatly to conceptualise how your system relates to the physical world, but you must be very careful with UML and OO design. That’s the point of OO – you’re looking at real world objects that your system will model. It is possible (and probable) to get stuck in an endless loop of pointless detail when doing this.
A well-written design document, to me, is far easier to follow, and allows a much richer description of what the code is really doing.
That’s why most good OO books recommend writing text, thinking through your use cases functionally rather than spending days drawing the diagrams and coming up with all sorts of pointless ones.
If done well, you can quite easily move from analysis and design to development without that last two week panic everyone knows about. However, most people are too inexperienced with OO modelling and get bogged down in detail. You can only use design patterns and other methods when you have a reasonable amount of experience under your belt.
“If done well, you can quite easily move from analysis and design to development without that last two week panic everyone knows about. However, most people are too inexperienced with OO modelling and get bogged down in detail. You can only use design patterns and other methods when you have a reasonable amount of experience under your belt.”
How about the other way? As part of the documentation for preexisting code? Say OSS.
Yeah, I saw the numbers regarding Java. I guess they were using the interpreter or something because those numbers aren’t right. In any case, I was more interested in the Lisp vs. C/C++ numbers, where Lisp (CMUCL) is still about 50% slower.
Some in the Lisp crowd reminds me of the rabid, linux zealot crowd. On the one hand they claim that their cause will cure cancer, but on the other hand (because of a personality disorder or something) they feel elite because they are the minority.
There’s lots of interesting concepts in Lisp, but the future of development are runtimes that can run a number of languages and libraries that provide automagic bindings to all its languges. For the most part when you develop in Lisp, you’re stuck with a Lisp system and it’s limited repository of libraries.
There are reasons that large telecommunications switching software, operating systems, and games are written in C/C++ and until the Smug Lisp Weenie ™ crowd realize the deficiencies of their system, then Lisp and it’s derivatives will be stuck in academic land being used by grad students with too much time on their hands.