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What are the key benefits of using UML models in software maintenance? I came across only few handful of papers regarding costs and benefits of UML models in software maintenance.
UML can ALWAYS be usefull in software related activity, but you must know what you are doing rather than using it because "my boss says UML is cool!".
Benefits of UML can depend on many factors. In some situations it is likely to be more beneficial. I try to mention some of them.
Likely to be more beneficial:
Larger and complexer is your subject, more benefit you can expect. Especialy when they are relationship between different aspects
If this SW maintenance means some extra development/extension, it could be very useful to use UML to clarify it. You can show existing system and the way it should be extended. You can of course always show the nre reqs.
if your system is already modelled in UML, you can use it to locate the problem and plan further enhancements
if both modeller and model reader know OO and have some experience in UML, they will almost always make it beneficial.
if you want to generate some code further more
if you need to support a system with no documentation, it could be usefull to document it first (use reverse engineering to import the code and organize it in UML)
if you plan to mainain this system for a long time and with lots of people
Maybe not so beneficial:
if the maintenance does not involve intensive extension/programming
if the subject under maintenance is too small - it can be more efficient to use natural languege or even spoken word
if either the person who models or who uses the diagram later is not skilled in OO and UML. If none of them is, forget about using UML and start learning it :)
if you already have some other kind of documentation
Imagine this:
Intro
you are a programmer assigned to do a maintenance of large legacy code base (thousands of files, damn many lines of code, written during several past years by several different people who had already go away, coding conventions and class libraries had changed several times during the original development)
Nobody likes that work, it is boring and repetitive so people are trying to get away as soon as they can and do some fresh and shiny development in some hype cool language. You are a 'junior maintainer' and so are most of your co-workers, so you have no wizard to ask and get magic fast and correct answers to your newbie questions.
The code is structured into many different files, many different classes (e.g. in Java to read the code of 20 classes you have to open 20 different files. In C in order to read the code you always have to read 2 files at the same time *.h and *.c, etc.)
Now you have to troubleshoot some problem. You are able to reproduce it in the test lab so you pick a debugger and start hunting the problem, where does the control and data flow and where is the hidden failure (may be some assert will fail or may be you'll spot something 'oh what a stupid bug' with your hawk eye).
Nightmare
No assert failed and you did not spot anything because it is C++ code and saying "hello" in C++ takes about 10 crypto graphy sentences where the "hello" is just in the middle. Most of the code is not written in the language you know but in a language of macros you have never heard about and calls to methods of classes you have never heard about.
Moreover you find out there are several code flows (threads) running at the same time and the data packet you are trying to track gets somewhere marshaled and queued for another thread to process and the debugger stopped at a waiting lock.
You're trying to picture what is going on using the debugger, patiently stepping into the unknown and taking notes on what the different words mean.
After several days of debugging, pulling your hair, cursing all the developers before you, seriously thinking about quitting this job
Relieve
you find some documentation. Someone wrote it using human words, designed for humans to read, explaining the basic concepts, giving links to places in code and other explaining documents and there are even some pictures in the docs.
And you look at the picture (UML diagram or some other pre-UML diagram) and now you can see where does the data flow, what are some of the classes you have already met supposed to do and where are the places you should look.
And you find that the UML diagrams saved you both many dead neurons but also countless hours of reading the code. As instead of reading and understanding thousands of lines of code you can just read hundreds of lines of explaining documents or read just several explaining pictures.
Conclusion
Powered by that new 'I see' knowledge you put breakpoints at several key places, inspect the variable values and you find that at this place X should not be 1. Because the docs said ... and you already know what are the dependencies of the X variable. So you put several other conditional breakpoints around and you finally find a bug in the logic as now the code flows through some combination of conditions that was not foreseen.
So you change few letters in one line of code, the bug is fixed, you have deserved your salary. The maintenance job is not such a nightmare anymore (though you still think about quitting the job) and the UML pictures helped.
So you draw some more UML-style diagrams explaining various inter dependencies (that you have learned the hard way) first using paper and pencil as small documentation one day is better than no documentation ever http://agilemodeling.com/essays/documentLate.htm
I know the conclusion is partially a sci-fi. As no maintainer will actually go and start creating missing documentation for a system that is going to be replaced in several years by newer and shinier. (s)he will just auto-create some UML diagrams by reverse engineering the code, throw them away after use and quit the job as soon as possible
But you get the picture of benefits of using UML models in software maintenance regarding costs?
First of all, sorry for the general title and, probably, for the general question.
I'm facing a dilemma, I always worked in c++ and right now I'm trying to do something very similar to one of my previous projects, which is to parallelize a single-target object tracker written in matlab in order to assign to each concurrent thread an object and then gather the results at each frame. In c++, I used boost thread API to do so, and with good results. Is it possibile in matlab? Reading around I'm finding it rather unclear, I'm reading a lot about the parfor loop but that's pretty much it? Can I impose synchronization barriers similar to boost::barrier in order to stop each thread after each frame and wait for other before going to the next frame?
Basically, I wish to initialize some common data structures and then launch a few parallel instances of the tracker, which shares some data and take different objects to track as input. Any suggestion will be greatly appreciated!
parfor is only one piece of functionality provided by Parallel Computing Toolbox. It's the simplest, and most people find it the most immediately useful, which is probably why most of the resources your research has found discuss only that.
parfor gives you a way to very simply parallelize "embarassingly parallel" tasks, in other words tasks that are independent and do not require any communication between them (such as, for example, parameter sweeps or Monte Carlo analyses).
It sounds like that's not what you need. From your question, I'm not entirely sure exactly what you do need; but since you mention synchronization, barriers, and waiting for one task to finish before another moves forward, I would suggest you take a look at features of Parallel Computing Toolbox such as labSend, labReceive, labBarrier, and spmd, that allow you to implement a more message-passing style of parallelization. There is plenty more functionality in the toolbox than just parfor.
Also - don't be afraid to ask MathWorks for advice on this, there are several (free) recorded webinars and tutorials on this sort of parallelization that they can point you towards.
Hope that helps!
It seems that I've finally got to implement some sort of threading into my Delphi 2009 program. If there were only one way to do it, I'd be off and running. But I see several possibilities.
Can anyone explain what's the difference between these and why I'd choose one over another.
The TThread class in Delphi
AsyncCalls by Andreas Hausladen
OmniThreadLibrary by Primoz Gabrijelcic (gabr)
... any others?
Edit:
I have just read an excellent article by Gabr in the March 2010 (No 10) issue of Blaise Pascal Magazine titled "Four Ways to Create a Thread". You do have to subscribe to gain content to the magazine, so by copyright, I can't reproduce anything substantial about it here.
In summary, Gabr describes the difference between using TThreads, direct Windows API calls, Andy's AsyncCalls, and his own OmniThreadLibrary. He does conclude at the end that:
"I'm not saying that you have to choose anything else than the classical Delphi way (TThread) but it is still good to be informed of options you have"
Mghie's answer is very thorough and suggests OmniThreadLibrary may be preferable. But I'm still interested in everyone's opinions about how I (or anyone) should choose their threading method for their application.
And you can add to the list:
. 4. Direct calls to the Windows API
. 5. Misha Charrett's CSI Distributed Application Framework as suggested by LachlanG in his answer.
Conclusion:
I'm probably going to go with OmniThreadLibrary. I like Gabr's work. I used his profiler GPProfile many years ago, and I'm currently using his GPStringHash which is actually part of OTL.
My only concern might be upgrading it to work with 64-bit or Unix/Mac processing once Embarcadero adds that functionality into Delphi.
If you are not experienced with multi-threading you should probably not start with TThread, as it is but a thin layer over native threading. I consider it also to be a little rough around the edges; it has not evolved a lot since the introduction with Delphi 2, mostly changes to allow for Linux compatibility in the Kylix time frame, and to correct the more obvious defects (like fixing the broken MREW class, and finally deprecating Suspend() and Resume() in the latest Delphi version).
Using a simple thread wrapper class basically also causes the developer to focus on a level that is much too low. To make proper use of multiple CPU cores a focus on tasks instead of threads is better, because the partitioning of work with threads does not adapt well to changing requirements and environments - depending on the hardware and the other software running in parallel the optimum number of threads may vary greatly, even at different times on the same system. A library that you pass only chunks of work to, and which schedules them automatically to make best use of the available resources helps a lot in this regard.
AsyncCalls is a good first step to introduce threads into an application. If you have several areas in your program where a number of time-consuming steps need to be performed that are independent of each other, then you can simply execute them asynchronously by passing each of them to AsyncCalls. Even when you have only one such time-consuming action you can execute it asynchronously and simply show a progress UI in the VCL thread, optionally allowing for cancelling the action.
AsyncCalls is IMO not so good for background workers that stay around during the whole program runtime, and it may be impossible to use when some of the objects in your program have thread affinity (like database connections or OLE objects that may have a requirement that all calls happen in the same thread).
What you also need to be aware of is that these asynchronous actions are not of the "fire-and-forget" kind. Every overloaded AsyncCall() function returns an IAsyncCall interface pointer that you may need to keep a reference to if you want to avoid blocking. If you don't keep a reference, then the moment the ref count reaches zero the interface will be freed, which will cause the thread releasing the interface to wait for the asynchronous call to complete. This is something that you might see while debugging, when exiting the method that created the IAsyncCall may take a mysterious amount of time.
OTL is in my opinion the most versatile of your three options, and I would use it without a second thought. It can do everything TThread and AsyncCalls can do, plus much more. It has a sound design, which is high-level enough both to make life for the user easy, and to let a port to a Unixy system (while keeping most of the interface intact) look at least possible, if not easy. In the last months it has also started to acquire some high-level constructs for parallel work, highly recommended.
OTL has a few dozen samples too, which is important to get started. AsyncCalls has nothing but a few lines in comments, but then it is easy enough to understand due to its limited functionality (it does only one thing, but it does it well). TThread has only one sample, which hasn't really changed in 14 years and is mostly an example of how not to do things.
Whichever of the options you choose, no library will eliminate the need to understand threading basics. Having read a good book on these is a prerequisite to any successful coding. Proper locking for example is a requirement with all of them.
There is another lesser known Delphi threading library, Misha Charrett's CSI Application Framework.
It's based around message passing rather than shared memory. The same message passing mechanism is used to communicate between threads running in the same process or in other processes so it's both a threading library and a distributed inter-process communication library.
There's a bit of a learning curve to get started but once you get going you don't have to worry about all the traditional threading issues such as deadlocks and synchronisation, the framework takes care of most of that for you.
Misha's been developing this for years and is still actively improving the framework and documentation all the time. He's always very responsive to support questions.
TThread is a simple class that encapsulates a Windows thread. You make a descendant class with an Execute method that contains the code this thread should execute, create the thread and set it to run and the code executes.
AsyncCalls and OmniThreadLibrary are both libraries that build a higher-level concept on top of threads. They're about tasks, discrete pieces of work that you need to have execute asynchronously. You start the library, it sets up a task pool, a group of special threads whose job is to wait around until you have work for them, and then you pass the library a function pointer (or method pointer or anonymous method) containing the code that needs to be executed, and it executes it in one of the task pool threads and handles a lot of the the low-level details for you.
I haven't used either library all that much, so I can't really give you a comparison between the two. Try them out and see what they can do, and which one feels better to you.
(sorry, I don't have enough points to comment so I'm putting this in as an answer rather than another vote for OTL)
I've used TThread, CSI and OmniThread (OTL). The two libraries both have non-trivial learning curves but are much more capable than TThread. My conclusion is that if you're going to do anything significant with threading you'll end up writing half of the library functionality anyway, so you might as well start with the working, debugged version someone else wrote. Both Misha and Gabr are better programmers than most of us, so odds are they've done a better job than we will.
I've looked at AsyncCalls but it didn't do enough of what I wanted. One thing it does have is a "Synchronize" function (missing from OTL) so if you're dependent on that you might go with AynscCalls purely for that. IMO using message passing is not hard enough to justify the nastiness of Synchronize, so buckle down and learn how to use messages.
Of the three I prefer OTL, largely because of the collection of examples but also because it's more self-contained. That's less of an issue if you're already using the JCL or you work in only one place, but I do a mix including contract work and selling clients on installing Misha's system is harder than the OTL, just because the OTL is ~20 files in one directory. That sounds silly, but it's important for many people.
With OTL the combination of searching the examples and source code for keywords, and asking questions in the forums works for me. I'm familiar with the traditional "offload CPU-intensive tasks" threading jobs, but right now I'm working on backgrounding a heap of database work which has much more "threads block waiting for DB" and less "CPU maxed out", and the OTL is working quite well for that. The main differences are that I can have 30+ threads running without the CPU maxing out, but stopping one is generally impossible.
I know this isn't the most advanced method :-) and maybe it has limitations too, but I just tried System.BeginThread and found it quite simple - probably because of the quality of the documentation I was referring to... http://www.delphibasics.co.uk/RTL.asp?Name=BeginThread (IMO Neil Moffatt could teach MSDN a thing or two)
That's the biggest factor I find in trying to learn new things, the quality of the documentation, not it's quantity. A couple of hours was all it took, then I was back to the real work rather than worrying about how to get the thread to do it's business.
EDIT actually Rob Kennedy does a great job explaining BeginThread here BeginThread Structure - Delphi
EDIT actually the way Rob Kennedy explains TThread in the same post, I think I'll change my code to use TThread tommorrow. Who knows what it will look like next week! (AsyncCalls maybe)
I'm doing some job interviews for the first time for my replacement. I want to know how they would approach a brownfields project, but am not really sure how to phrase the question.
I'd like to know what their attitude is: e.g. throw out and rewrite, use a tool to refactor, step through the code and understand, what books they've read (e.g. "Working Effectively with Legacy Code").
How do you find out how someone takes on brownfields software development?
When interviewing, try to engage in scenario brainstorming or role playing, not definition swapping. In this case try to engage an applicant in telling their story about what they would expect "...when taking over responsibility for the main finance system, which this department and that group use daily for these things, and there are a couple things that are wrong with it today, and oh by the way, there is a upgrade release scheduled for three months from now that will allow direct integration with this new banking partner for 1099 processing". Make the scenario specific and real for your situation, and get them talking.
The important thing is to draw out from them not only what they would do, but almost as importantly, what they know to expect. If your candidate sits across from you and weaves a story about getting up to speed in a couple days and making major changes up through production by next Friday, without asking any of the important questions and impressing you with their effectiveness, doubt their experience (and if you are in a regulated industry or, unfortunately, Big Company, possibly their sanity). If instead they ask good questions about what the environment is like today, what's the review process, who makes the decisions about functionality, is there a testing environment, is the code testable or are there unit tests (gasp) in place, and what happens today if a change needs to get in place by Friday - hey, they've probably been here and done this before.
You of course want to hear how they would make sure existing functionality works and time bombs aren't being set but you also want to hear them making reference to things they would be doing so that this project becomes better, easier to work with, and more fun over time. The activities they specifically are engaging in to turn the inherited legacy project into a rocking world of fun should come through in their storytelling. I mean, they are planning on doing that, right?
Great interviews are conversations and experience sharing and story telling. Draw those stories out, bounce them against the b.s. shield, and go.
This sounds like a great interview question. Why not just ask them
what steps they'd take on inheriting/maintaining/extending a badly written legacy codebase, or how do you determine when a codebase needs to be refactored? Another option would be to give them a medium sized piece of spaghetti code and ask them how they'd extend it.
Lots of good suggestions for answers here.
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From Wikipedia:
The Last One was a unique software
program in 1981 which
took input from a user and generated a
program in BASIC which could then be
run. It is an example of a program
generator.
The software was not a programming
language, since unlike most
programming languages, programs were
generated by the user selecting
options from menus that would form the
basis of the generated code. This was
done in a logical sequence that would
eventually cause a program to be
generated in BASIC. At any time, the
user could elect to view a flow chart
showing the current progress of the
program's design. 2
But Wikipedia didn't say what became of this program. How popular/unpopular was it, and how many people use it? How and when did it meet its demise, or is it still available?
More information available here.
Here's the current story AFAICT: this article mentions that the consulting firm they formed way back then to put TLO into play was named DJ `AI' Systems and is now tloconsultants.com (tlo == The Last One). Cha-ching :-)
My guess (after a 2min site scan) is that they grew their business by continually expanding what appears to be business-oriented expert system "modules" that the generated code ran against (and also perhaps even assisted in or guided some of the code generation, most likely for the code that targeted its own routines) and then incorporate the knowledge of how to use the new modules back into TLO. Very impressive, especially for 1981 and with the engine that knew when it didn't know enough -- ScHrIaTp! I wish my manager had 1/10th that functionality.
And you gotta love that it took five minutes to generate 100 bug-free lines of BASIC code.
I'm curious as to whether they ever "closed the loop" (my term) because I didn't see it mentioned (as I didn't fully read it due to that dang corporate job and its fake-time-based insanity) as to whether they actually reached the point where its own representation was manipulated within it in order to generate the next version of TLO itself. The name "The Last One" suggests to me that David James fully understood the meaning of manifesting a piece of software capable of presenting its own representation to the user (== programmer) for modification with the end purpose being to generate its own subsequent version.
All such self-repping-and-editing programs (live processes are IMO far more difficult while being also tantalizingly more interesting) are actually, from my perspective, equivalent in the sense that they are all 'functions that transform functions that transform functions' (how about 'FtTFtTF's -- appropriately absurd and lovely, IMO :-)
Trying to wrap one's head around how to implement such a beautiful piece of software in the face of its myriad possibilities is the kind of programming puzzle that brings home why MDD is both the current brightest idea while simultaneously being rarely used in real-world projects. Your brain better be firing on ALL cyllinders to go treading that path. How long has it taken Simonyi and his billions?
I am also curious as to whether there are infinite variations of FtTFtTFs or just lots and lots of lots of them.
Enjoy!
"Lasting Peace and Happiness for all Human Beings!"
Well, I found a blog article by a person who did a major interview with the creator of "The Last One". At the time of the writing of the article (2007), he was still working with one of the creators of "The Last One". You can probably ask him what became of it.
TRUE STORY!!!
I was the director when TLO it first came to America from England. The company spent so much time trying to find the right marketing avenue that the bubble past them by. We all did 180 seminars with crowds of 50 to 100 each in as many days. There was Scot Norton, Gil Savage, Rodger David and Richard Housand and me, Michael Bartolucci. We had an exclusive for the US which I cry about every time I think about it. We decided to right an accounts receivable and give it away with the program. Then in a week it changed to General Ledger, then AP and so on. Had we took one idea (AR)and ran with it, I think we could of had our dream come true. It wad a viable program. We took a voice generator that was present it the 1981 Computer Conference and teamed up with them. I wrote a BASIC program while in front of 50 press members (mostly from Europe).It was error free and took about 20 minutes that created a simple database to create and it would add, change, and delete members of the database from a central menu. We did this on the third day of the Conference in Houston TX. Wen our marketing failed so did the company. I understand the original company took it into receivership and decided not to pursue it further.
That was my second job in as many years. I continued on for another 38 more very successful years in the computer field.
The next step of evolution were 4GL languages and CASE tools. After that, we have UML and today, MDD.
All of those come with more or less amount of tool support to generate code from some abstract "input". All of them more of less failed for the general case since the general case isn't abstract enough to map it to some formal and simple input.
Today, MDD is a solution for highly repetitive tasks and other programming tasks that can be easily abstracted. Think "copy data out of XML" (highly abstract, good tool support) vs. "calculating the gravity field of a black hole" (very specific, no reuse, little tool support).
[EDIT] As for the history of "The Last One", probably no one adopted it. Code generators always were a bit neglected. My guess is that this is because of the many pitfalls: If you need a million lines of code that look all the same, then a code generator is really cool. But you never need that. You need a million lines of code that are somewhat similar, where "somewhat" is often different from line to line.
But if no one here can answer what happened to the old program, I suggest to ask this question on the respective Wikipedia discussion page (see "discussion" at the top of the wiki page). People who wrote the article might know.
The Last One (TLO) was written by a bloke called David James, who was funded by "Scotty" Banbury, at the time a businessman whose main interest was a company called "Hilltop Tyres", based near Axminster in Devon.
It started life as a simple program generator on 6502 based machines, particularly the Commodore Pet and the Apple II. After a while, David dropped out and Scotty morphed into the principal author. He recoded the product as a meta generator, creating a new language which could, in theory, be retargeted at other languages. He spent a lot of time on C as a target but I don't know if he got that going, as I lost contact with Scotty and the product in the early 'nineties.
These language generators were popular at that time, another being Sycero/DB which could generate both Clipper/DBase code and quite clean ANSI C.
When first put on the market, both TLO and Sycero were useful tools for the bottom end of the market and their output was used even by quite large companies. The problem was that they generally used canned modules and simple substitution to create the target programs, although I think Scotty was experimenting with something that looked a bit like a bi-directional parser, able to translate BASIC into TLO as well as the other way around.