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To explain my question more i am going to explain what I'm doing.
I am doing my final project at uni and i don't want to be wasting my time so i want to know if this is possible.
I have a digital forensic report that gets filled out by every investigator and it goes to the case officer to review before carrying on with a case. I want to make that easier by creating a html form that can take the investigators notes and put them in the form for them.
Is this possible?
Building such an application is perfectly possible, and without much fuzz, depending on the scope of your target and if you have already built an web application before.
If you just have to upload documents through a web form, and these will be appended to a final document (may be a PDF which will be rendered on the website) such that the case officer will have less work with reviewing as he can just scroll through, this could already do the job.
Since you are not asking about handwriting recognition or OCR, you do not seem to have any specifications on how to do this yet?
Also do you have a legacy system in which you will have to integrate your application? Or is it a greenfield project where you will also build the 'html forms' by yourself?
But you should get your supervisors do their job and get them to define the applications scope for you properly.
Otherwise this might turn into a neverending story via scope creep when you try to recognize all the handwritings on the documents (not just block lettering), have to support a dozen input formats (not just pdf), ...
When screen-scraping, what are the "gotcha"s to look out for?
The inspiration for this is: my spouse's co-worker asked me to scrape all the pages from a Blogger-hosted blog that her friend with cancer kept in her final months and this lady wanted to keep all of the posts in case the blog were ever deleted. I eventually found a free tool that was barely good enough.
One issue with scraping many Blogger pages is that there's often a navigation menu where you can click on the triangles to expand the post lists by year or month. These little buggers created insane amounts of duplicate content because you'd have the same page over and over again with different combinations of the menus being expanded/collapsed. In Blogger's case I'm not sure this is avoidable since the links are all formatted as real http links and not obvious JavaScript calls. Still, it got me thinking:
If you were to scrape a website, what kinds of potentially non-obvious things would you compensate for?
Do not use regex to scrape
While regular expressions can be good for a large variety of tasks, I find it usually falls short when parsing HTML DOM. The problem with HTML is that the structure of your document is so variable that it is hard to accurately (and by accurately I mean 100% success rate with no false positive) extract a tag.
What I recommend you do is use a DOM parser such as BeautifulSoup or equivalent (SimpleHTMLDom in PHP).
Some may think this is overkill, but in the end, it will be easier to maintain and also allows for more extensibility.
A regular expression could be devised to achieve the same goal but would be limited. For example, developing a regex to get the src and alt tag would force the alt attribute to be after the src or the opposite, and to overcome this limitation would add more complexity to the regular expression.
Also, consider the following. To properly match an <img> tag using regular expressions and to get only the src attribute (captured in group 2), you need the following regular expression:
<\s*?img\s+?[^>]*?\s*?src\s*?=\s*?(["'])((\\?+.)*?)\1[^>]*?>
And then again, the above can fail if:
The attribute or tag name is in capital and the i modifier is not used.
Quotes are not used around the src attribute.
Another attribute then src uses the > character somewhere in their value.
Some other reason I have not foreseen.
So again, simply don't use regular expressions to parse a dom document.
I screen scrape a lot. Some advice:
Emulate a User-Agent string for some browser you want to use. Different websites frequently return very different results depending on what your user agent is. If they don't recognize the User-Agent they will often revert to lowest common denominator, so it's usually best to start with some recent browser. (For example the World of Warcraft Armory returns beautiful, easy to parse XML if it thinks you're a recent Firefox. If it doesn't know what you are it sends terrible HTML).
Be polite to the site you're scraping; don't hit it too hard. Your scraper will go faster if you multi-thread it, making many requests at once, but that will annoy the site owner.
Be smart about error handling. Do not write code like while (1) { makeRequest(); }. If your code or the server throws an error a loop like this will immediately fetch another request, generating another error. It can get ugly quickly. Handle errors well and consider putting in sleeps or exits if you see a lot of errors.
When developing your parsing code, test against a cached version rather than hitting the server every time. Will make your development go faster and is the basis of a simple test suite.
First, I'd check for an RSS feed. On blogger, you just have to add /rss to the root url, if I remember correctly.
Then I'd check if there isn't already some tool to scrape blogger.
Then if there's no RSS feed, and no existing tool, I'd give up and do it by hand with copy/paste. Unless we're talking 5000 pages, it's much faster and easier that way. Take it from someone who's tried.
If you have access to the actual account, blogger has an export function.
edit: Or of course, you could try mechanical turk.
As far as gotchas are concerned..It's usually a good idea to limit the amount of requests made over a certain period of time. Smashing a site with alot of requests in a short space of time is a good way to have your requests rejected.
Aside from the technical considerations, make sure your not putting yourself at legal risk. Most large sites have specific legal language in their terms of use that disallows programmatic access to their services via an automated computer program, and also, the obvious copyright concerns.
From a technical standpoint, definitely use a DOM parser library and you'll save loads of time. Many provide the ability to read HTML into an XML structure that can be queried using XPath to find exactly what you need.
If you know someone who has access to the account, they can use Blogger's export "Export blog" feature.
While thinking about software-engineering in general I came across the question why we don't see any improvements in the way we write/document code.
Think about it: There has not been a revolutionary improvement since we've moved from punch cards to text editing. The last improvement I've seen is syntax highlighting and context sensitive help (e.g. Intellisense or ctags). Not something I would call revolutionary.
That makes me wonder: Why is it so?
I'll start with something I miss badly:
Lots of my code deals with geometry.
For documentation describing geometric relationships always ends up in a big heap of hard to read mathematical stuff (due to the lack of proper equation type-setting in ASCII). However, if I could embed a little drawing or scribble into the code everything would be much easier, neater and better to be understood.
What can you think up that would make your coding/text editing/documention tasks easier?
I'm surprised that nobody has yet mentioned No Silver Bullet. In 1986 (!), Frederick Brooks predicted that:
There is no single development, in either technology or management technique, which by itself promises even one order-of-magnitude [tenfold] improvement within a decade in productivity, in reliability, in simplicity. [...] We cannot expect ever to see two-fold gains every two years."
And in 23 years, he's been proven right. We've come up with a number of things such as syntax highlighting and Intellisense which have improved productivity significantly, but certainly not by an order of magnitude. As time marches on, we'll continue to make several incremental improvements, but the fact is there is no silver bullet: there's not going to be some magical revelation in the way we write code that will improve productivity by an order of magnitude.
I'm suprised that no one seems to have mentioned Donald Knuth's seminal Literate Programming - write your code as if it were a book or a scientific paper.
There has not been a revolutionary improvement since we've moved from punch cards to text editing
Never used a line editor, have you?
But seriously, text (especially in the representations chosen for modern languages) is
easily processed
fairly easy to specify
information dense
precise
Anything that comes along to replace it has to be a net win across all four of those properties. Not easy.
I disagree. We do have changes, small, but changes.
How common is the "for each" construct? Compare it to 20 years ago. How about the Domain Specific Languages movement? What about the idea that we should code in layers? How about Behavior Driven Development? Coding by complying to a specification... which writes a nice document as output when all runs fine. How about the standarization of regular expressions? PCRE. What about Alan Kay's group's DSL related work on "Moore's Law for Software", which explored a more advanced implementation of Cairo and generated TCP/IP code using diagrams from RFCs?
Documentation is a two way dialog. Both as code being more understandable and people learning this special language. You wouldn't say that German needs documentation if you know German. I know natural languages are very far away from computer languages, but there's a movement to make code more expressive. It's not about the new tools, it's about how we are coding.
One thing I've done recently in some of the more math-heavy sections of my application is to include the LaTeX markup for the particular equation as a comment/docstring. Right now, I just copy-paste into an online equation editor, but it would be very helpful to see the formula itself (with things like Greek letters and sub/superscripts) rather than a bunch of ASCII code.
Source Code In Database. In a nutshell, source code is parsed and put into a database. You'd then need an integrated IDE to view and edit the code, but at this point, syntax is decoupled from format. YOUR IDE could show you a program in a way that's completely different from someone else's, tuned to the task you're working on. I'd list some specific examples, but that article covers pretty much everything.
I'm surprised nobody mentioned it - javadoc is basically HTML, so there's nothing preventing you from embedding images (or anything else) in code. Simple, effective and ubiquitous, it's one of the things Java did right.
DrScheme let's you do these things. Here's the things you can insert from the PLT website:
http://docs.plt-scheme.org/drscheme/Menus.html#(part._.Insert)
3.1.6 Insert
Insert Comment Box : Inserts a box that is ignored by DrScheme; use it to write comments for people who read your program.
Insert Image... : Opens a find-file dialog for selecting an image file in GIF, BMP, XBM, XPM, PNG, or JPG format. The image is treated as a value.
Insert Fraction... : Opens a dialog for a mixed-notation fraction, and inserts the given fraction into the current editor.
Insert Large Letters... : Opens a dialog for a line of text, and inserts a large version of the text (using semicolons and spaces).
Insert λ : Inserts the symbol λ (as a Unicode character) into the program. The λ symbol is normally bound the same as lambda.
Insert Java Comment Box : Inserts a box that is ignored by DrScheme. Unlike the Insert Comment Box menu item, this is designed for the ProfessorJ language levels. See ProfessorJ.
Insert Java Interactions Box : Inserts a box that will allows Java expressions and statements within Scheme programs. The result of the box is a Scheme value corresponding to the result(s) of the Java expressions. At this time, Scheme values cannot enter the box. The box will accept one Java statement or expression per line.
Insert XML Box : Inserts an XML; see XML Boxes and Scheme Boxes for more information.
Insert Scheme Box : Inserts a box to contain Scheme code, typically used inside an XML box; see XML Boxes and Scheme Boxes.
Insert Scheme Splice Box : Inserts a box to contain Scheme code, typically used inside an XML box; see also XML Boxes and Scheme Boxes.
Insert Pict Box : Creates a box for generating a Slideshow picture. Inside the pict box, insert and arrange Scheme boxes that produce picture values.
You also insert your unit tests with the code that you're testing. Pretty neat stuff.
I think integrated IDEs with semantic highlighting and **semantically-constrained suggestions* (a la IDEA or Eclipse) are a huge advancement.
But that happened 8-10 years ago.
Template-based programming feels useful never seems to catch on. Recently I was impressed with a demo of the Meta-programming system, which leverages the interactive nature of the IDE to simplify the task of writing templates and what are (essentially) type-aware macros.
Meta-programming might help you define geometry-based macros that would substitute for a number of lines of code. I could imagine something that let you embed a more-readable 'math language' inside Java, and then parses its contents into something machine-readable.
I'd say version control was a pretty huge leap in how we work. The ability to keep a full record of every change anyone has made to the codebase, and to revert changes where necessary, has made a big difference.
I certainly respect Fred Brooks' argument No Silver Bullet, but I think the way we write code is nowhere near optimal, so there is lots more room for improvement. I tried to explain this in my book.
We're all familiar with "code golf", where you compete relentlessly to minimize something. That is a good way to approach the minimum possible value of that something.
What's great about this is that you are allowed, even encouraged, to break from traditions, prior conceptions, accepted wisdom, in the quest for winning. In short, you learn new things.
If the measure to be minimized is wall-clock execution time, you can do aggressive optimization.
If the measure is source code size (lines or characters) you get "code golf".
The measure I like best is "edit count". That is, given a code base, suppose a new requirement comes along. That requirement is implemented, completely, by editing the code base. Then a "diff" is done from old to new code base. The number of differences found is the edit count. Averaged over the set of likely new functional requirements, that is the measure to minimize.
If this is done aggressively, being free to contradict all conventional wisdom, the code base approaches a state I would call a domain-specific language (DSL). In this language, concepts expressed in code are in nearly 1-1 correspondence with problem-oriented concepts. In this state, it is not easy for the source code to be self-inconsistent (i.e. have bugs) because the fewer edits that have to be made to the source code, the fewer chances there are to make a mistake. It's also the case that such code tends to be short. But unlike "code golf" it tends to be very clear, because it maps the problem concepts so clearly.
So, tools and techniques that help in minimizing edit count can, in my opinion, be considered "silver bullets". DSL is one such. Code generation is another. My favorite optimization technique is another. For coding dynamically changing UIs there is differential execution. There are bound to be more, waiting to be discovered. Of course, everything depends on the training and experience of the "marksman" (the coder).
I think there are lots of new ideas to be discovered. The trick is to tell the difference between the ones that move us forward, versus the ones that hold us back.
I think this is where Doxygen and other documentation systems help. If we can embed small, discrete comments that link to other information such as:
/* help: fooimg.png */
And then have an external documentation system do that, then great.
Even better would be allowing our text-editor to treat those things as hyperlinks to external documentation.
I would reference a drawing as a reference in the code documentation. I see no reason why you can't have footnotes in code.
The ability to make a section of code read-only is something I've wanted
It sounds like you might be interested in Jonathan Edward's research. See, for example:
"The Summer of Code"
"What's next?"
"The future of programming"
Diffing and searching pictures is hard. Diff and search are very important to programmers. Using pictures instead of text is only a marginal improvement in many situations, it has some drawbacks, and it requires general acceptance before it's really worth doing (since you don't make things more understandable if your reader doesn't grok what you've done).
Plus, programmers have a million little tricks that make their lives easier, based on text representations of code, that they'd lose if you gave them code to read that was expressed in anything other than text. Sure, they might replace or re-implement those tricks over time, but in the short term they're gone.
You don't see lawyers switching from English to little back-of-a-napkin diagrams in contracts, either (the Creative Commons licenses try, but cannot make the picture be the formal representation of the contract). Probably for similar reasons.
If someone comes up with a programming language and IDE that, on balance, beats text-based ones; and successfully markets it; then you'll see the start of a revolutionary shift from text to a new format. If nobody comes up with any such thing, then we're not missing out. If someone comes up with something that is more productive but it doesn't gain traction because of independent advantages of other technologies, then that loss is the price we pay for free-market capitalism. Perhaps the ideas will be recycled eventually...
That said, integration between code and documentation could clearly be improved, and there are many efforts underway to do so, using various techniques with varying success. Again, the problem is that any particular cunning plan can in practice only really be implemented in one or a few languages and development environments at a time, and so has difficulty proving that it really is better. Embedding documentation in code is possibly the only universal advance since the invention of the API...
I think there's still a lot that can be done with text, though. For example, debugger technology makes a big difference to programmer productivity in certain common circumstances (namely: when a test fails or something else unexpected happens, but it's not obvious what the faulty assumption is in the code you're looking at). There may be lower-hanging fruit in terms of making programming better, than the actual business of expressing the program.
The last improvement I've seen is
syntax highlighting and context
sensitive help
Then you haven't looked much. Modern IDEs can do far, FAR more than that, namely show you the semantic structure of code (e.g. inheritance hierarchies) and even manipulate it (automatic refactoring) or enrich it with external data (such as who last changed a particular line of code).
I've used emacs, I like text macros. But, what I really want is parse macros. I'd like my editor to expose the machinery behind refactoring in such a way that I can write my transformations on the parse tree of the language itself.
For example, Python added += at one point when my code was littered with x = x + 1 lines. If I could have written a search and replace command that worked on the parse tree, I could have quickly cleaned up large amounts of my source code.
So, I want standard search and replace, but I want it at the level where the structure of my code has meaning, at the abstract syntax tree.
If you've ever used ReSharper, each of its refactorings and recommendations are written in the manner I describe, they find a pattern in the parse tree and suggest a replacement, or for a refactoring, apply a known replacement. I want access to that machinery for my own tasks!
Have you used Doxygen or similar for documenting your code? You can add links to images, and other file types (often stored in same directory as source code) that will get sucked into the generated documentation. I realize that this is one step removed from seeing the detail directly in you favorite editor but it definitely improves how we document our code.
Programming languages are a specialized form of mathematical notation, since you can express a programming language mathematically. Notation changes slowly, and so we don't get fast progress in our languages. Mostly, we advance when we come up with a new thing to fit into the notation, like using i to refer to the square root of negative one.
There are documentation schemes that allow you to embed things other than text. There was at least one programming scheme, Donald Knuth's Web, that allowed you to have a presentation and an execution version of a program (unfortunately, the base source code, the stuff you'd actually hack, was rather messy).
You could easily have a text editor that could treat comments as HTML, provided of course it could recognize comments as it saw them.
I've been thinking a lot about how to make coding faster and more efficient for the past years, always trying to keep it realistic and doing minimalistic implementations. Those are not revolutionary ideas, but since the original poster talked about the punching card to code typing transition, I thought of talking about other ways of communicating to the computer what we want to program.
My ideas are visual or vocal programming. The motivation behind is that there are only a number of ways a loop can be efficiently programmed, and an aware IDE could make some smart code substitution decisions depending on inputs other than typed lines of code.
Visual programming vs Coding: encapsulate (literally) code into "boxes" which have inputs and outputs, and connect them together across a horizontal timeline. This is a high-level concept that would be intrinsically interesting for multithreading development since you can have multiple lines or threads happening at the same time. Every process can be divided into a "box", no matter how you see it. Sending an e-mail in its most basic form is a box which takes an email as input and outputs a success/fail signal. Since the boxes and the lines are distributed across a timeline, the notion of time and event chronology isn't lost and feedback lines are possible.
Vocal programming vs Coding: The effectiveness of this technique would revolve around the effectiveness of the vocal syntax decided to create code and move the cursor. For example, you can say to the microphone "for variable zero to 10" and the system will automatically generate the following code placing the cursor inside:
for (x=0;x<10;x++){
// Cursor would be there after after the call
}
In terms of usability, you would need to be in a relatively silent room to minimize other sounds that might harm the voice recognition so this technology could be used in specialized environments mostly.
This is the result of my extensive programming experience using a wide range of hardware and programming languages. Let me know what you guys think, I'd love having a constructive discussion about that.
A few weeks back the "Intentional Software" created quite a buzz about their new language. I've yet to watch the presentation, but here is a quote from a review by Martin Fowler:
They started worryingly, with the
usual unrevealing Powerpoints, but
then they switched to showing the
workbench and the curtain finally
opened. To gauge the reaction, take a
look at Twitter.
#pandemonial Quite impressed! This is sweet! Multiple domains, multiple
langs, no question is going unanswered
#csells OK, watching a live electrical circuit rendered and
working in a C# file is pretty damn
cool.
#jolson Two words to say about the Electronics demo for Intentional
Software: HOLY CRAPOLA. That's it, my
brain has finally exploded.
#gblock This is not about snazzy demos, this is about completely
changing the world we know it.
#twleung ok, the intellisense for the actuarial formulas is just awesome
#lobrien This is like seeing a 100-mpg carburetor : OMG someone is
going to buy this and put it in a
vault!
Two quotes come instantly to mind:
"If it ain't broke, don't fix it."
"Use the best tool for the job."
Of course, although the core code is still written as text, alll the tools and libraries have changed massively since the days of punched cards.
This has been touched on by others, and it wouldn't revolutionise programming, but anyway...
I think it would be nice if code editors moved slightly beyond plain text editors. Even with syntax highlighting and code completion (which I think are incredibly good things), the editors of today (at least, the ones I use) still display exactly the same ASCII text (or whatever encoding is used) that is in the source files. I would be interested to see how well it would work if editors displayed, for example (some examples are more adventurous than others):
Comments in a text box with a light-blue background and no // or /* ... */ visible
Javadoc comments could have semi-rich text editing support (for those who do HTML Javadoc comments) (seriously, I would appreciate it if code editors rendered Javadoc comments as HTML because they're not the easiest to skim over when their HTML as plain text)
Functions in text boxes that could be collapsed to show only the signature (the collapsing can be done by current editors) and can be dragged around as boxes
Lines between function boxes to indicate how functions are connected
Zooming out so that rather than seeing a single source file (class in many languages) you can see multiple files and the way connect to each other (this would essentially be building UML-like diagramming directly into the code editor)
I think this (in my mind at least) would work without requiring additional markup in the source files so users of plain text editors wouldn't be disadvantaged by having all this extra markup cluttering the files.
Part of the problem might stem from the fact that when you don't code we don't call it programming: Assembling modular components using a GUI for instance.
You might be interested in these alternative programming "languages".
[Ladder][1], designed to mimic the way relay-logic-schemes work. Horrible IMO, but easy to understand for the old guys who did logic with sticks and stones. [http://www.amci.com/tutorials/images/ladder-diagram.gif][2]
[SFC, Sequential function chart][3], designed to simplify parallell programming. Code is written into boxes and these boxes can be placed paralell to each other and will thus execute simultaneously. By connecting the end of several boxes you can syncronize events. Very common for automation applications.
[Mathematica][5]!!!, Might not be the best programming language but the syntax highlighting(if you can call it that) is awesome! For example you can input a matrix by seeing the matrix nicly aligned instead of a huge double[][]. Graphs can be inserted in the code and the formatting of mathematical expressions looks like it does when you write on a paper. No more paranthesis-madness or long Math.PI expressions that really only need one character. And best of all, the files are just plain text even if it is rendered nicely in the editor!
Debuggers is also an area where lots of improvement has been done. Debuggers with replay are starting to come and also visual debuggers where data can be modified in real time. Edit and continiue is also a feature i wouldn't want to live withot.
WTF "new users can only post a maximum of one hyperlink", you will have to google the stuff i originally added to this post >:(
A brain-to-computer translator. Typing is the real
bottleneck. It really just needs to derive the algorithms I
think up and convert that to machine code.
I would say a lot of the newer languages are pretty great at
quickly creating algorithms. The improvements aren't so much
revolutionary now as they are evolutionary.
Dare I say it might actually be a new development language (perhaps even a new paradigm) to take us through such revolution;
I think you might want to take a look at Leo. This is one guys attempt at answering what you're asking about. I still can't wrap my VIM head around it personally, but others take to it quickly. It's not just a programming IDE, but more of an information organizer. It's written in Python, but I don't see why you can't code in other languages with it. The power of Leo is not so much the language, but the ability to express your thoughts and organize them whether it be in code, diagrams, images, or diagrams. Look over the tutorial and examples to get a feel for it. You might like it.
Automated semantic source code transformations, where a program can be reliably examined and manipulated by using an abstract interface/frontend to it that is aware of the underlying semantics.
So that source code can be queried and dealt with pretty much like a SQL database.
Allowing you to do static analysis of source code and refactor even complex source code by doing something along the lines of:
FIND CALLERS OF FUNCTION "foo" WHERE SIGNATURE("int","int","char*") AND RETURN_TYPE("bool");
...
RENAME MACRO "max" TO "maximum" IN FILE "macros.hxx";
RENAME NAMESPACE "prj" TO "project";
RENAME SYMBOL "OLDFOO" IN NAMESPACE "project";
RENAME FUNCTION "log" TO "show_log";
RENAME CLASS "FOO" TO "OLDFOO";
RENAME METHOD "FOO::inc" TO "FOO::increment";
...
CHANGE SIGNATURE IN FUNCTION "foo" WHERE SIGNATURE("int","int") TO SIGNATURE("double","double");
CHANGE SIGNATURE IN METHOD "myClass::handle" WHERE SIGNATURE("char") TO SIGNATURE("unsigned char")
MOVE FUNCTION "foo" in FILE "stuff.cc" TO "foo_funcs.cc";
I have heard many developers refer to code as "legacy". Most of the time it is code that has been written by someone who no longer works on the project. What is it that makes code, legacy code?
Update in response to:
"Something handed down from an ancestor or a predecessor or from the past" http://www.thefreedictionary.com/legacy. Clearly you wanted to know something else. Could you clarify or expand your question? S.Lott
I am looking for the symptoms of legacy code that make it unusable or a nightmare to work with. When is it better to throw it away? It is my opinion that code should be thrown away more often and that reinventing the wheel is valuable part of development. The academic ideal of not reinventing the wheel is a nice one but it is not very practical.
On the other hand there is obviously legacy code worth keeping.
By using hardware, software, APIs, languages, technologies or features that are either no longer supported or have been superceded, typically combined with little to no possibility of ever replacing that code, instead using it til it or the system dies.
What is it that makes code, legacy code?
As with plain legacy, when the author is dead or missing, you as a heir get all or some of his code.
You shed some tears and try to figure out what to do with all this rubbish.
Michael Feathers has an interesting definition in his book Working Effectively with Legacy Code. According to him legacy code is code without automated tests.
It is a very general (and oft abused term) but any of the following would be legitimate reasons to call an app legacy:
The code base is based on a language/platform which is entirely unsupported by the manufacturer of the original product (often said manufacturer has gone out of business).
(really 1a) The code base or platform on which it is built is so old that getting qualified or experienced developers for the system is both hard and expensive.
The application supports some aspect of the business which is no longer actively grown and for which alterations are extremely rare, normally to fix it if something entirely unexpected changes around it (the canonical example being the Y2K issue) or if some regulation/external pressure forces it. Since both reasons are pressing and normally unavoidable but no significant development has occurred on the project it is likely that those people assigned to deal with this will be unfamiliar with the system (and it's accumulated behaviours and intricacies). In these cases this would often be reason to increase the perceived and planned for risk associated with the project.
The system has/or is being replaced with another. As such the system may be used for much less than originally intended, or perhaps only as a means of viewing historical data.
Legacy generally refers to code that is no longer being developed - meaning that if you use it, you have to use it on its original terms - you cannot just edit it to support the way the world looks today. For example, legacy code has to run on hardware that may not exist today - or is no longer supported.
According to Michael Feathers, the author of the excellent Working Effectively with Legacy Code, legacy code is a code which has no tests. When there is no way to know what breaks when this code changes.
The main thing that distinguishes
legacy code from non-legacy code is
tests, or rather a lack of tests. We
can get a sense of this with a little
thought experiment: how easy would it
be to modify your code base if it
could bite back, if it could tell you
when you made a mistake? It would be
pretty easy, wouldn't it? Most of the
fear involved in making changes to
large code bases is fear of
introducing subtle bugs; fear of
changing things inadvertently. With
tests, you can make things better with
impunity. To me, the difference is so
critical, it overwhelms any other
distinction. With tests, you can make
things better. Without them, you just
don’t know whether things are getting
better or worse.
Nobody is gonna read this, but I feel the other answers don't get it quite right:
It has value, if it wasn't useful it would've been thrown away long ago
Its hard to reason about because either of
Lack of documentation,
Original author cannot be found or forgot (yes 2 months later your code can be legacy code too!!),
Lack of tests or typesystem
Doesn't follow modern practices (ie no context to hold on too)
There is a requirement to change or extend it.
If there isn't a requirement to change it, it isn't legacy code
since nobody cares about it. It does its thing and there is nobody
around to call it legacy code.
A colleague once told me that legacy code was any code that you hadn't written yourself.
Arguably, it's just a pejorative term for code that we don't like any more for whatever reason (typically because it's not cool or fashionable but it works).
The TDD brigade might suggest that any code without tests is legacy code.
Legacy code is source code that relates to a no-longer supported or manufactured operating system or other computer technology.
http://en.wikipedia.org/wiki/Legacy_code
"Legacy code is source code that relates to a no-longer supported or manufactured "
Any code with support (or documentation) missing. Be it:
inline comments
technical documentation
spoken documentation (the person who wrote it)
unit tests documenting the workings of the code
For me legacy code is code that was written prior to some paradigm shift.
It may still be very much in use but it is in the process of being refactored to bring it into line.
e.g. Old procedural code hanging around in an otherwise OO system.
Code (or anything else, really) becomes "legacy" when it has been replaced by something newer/better, and yet despite this it's still used and kept alive "in the wild".
Preserving legacy code is not so much an academic ideal as it is keeping code that works, no matter how poorly. In many conservative enterprise situations, that would be considered more practical than throwing it away and starting again from scratch. Better the devil you know...
Legacy code is code that is painful/expensive to keep current with changing requirements.
There are two ways that this can happen:
The code is unsuitable for change
The semantics of the code have been swapped out to silicon
1) is the easier of the two to recognize. It is software that has fundamental limits making it unable to keep up with the ecosystem around it. For example, a system built around O(n^2) algorithm won't scale beyond a certain point and must be re-written if requirements move in that direction. Another example is code using libraries that are not supported on the latest OS versions.
2) Is harder to recognize, but all code of this kind shares the characteristic that people are afraid to change it. This could be because it was badly written/documented to begin with, because it is untested, or because it is non-trivial and the original authors who understood it left the team.
The ASCII/Unicode chars that comprise living code have semantic meaning, the "why's", "what's" and to some degree the "how's", in the minds of people associated with it. Legacy code is either un-owned or the owners do not have meaning associated with large portions of it. Once this happens (and it could happen the next day with really poorly-written code), to change this code, someone must learn it and understand it. This process is a significant fraction of the time it takes to write it in the first place.
The day you're afraid to refactor your code is the day when your code has become legacy.
I consider code "legacy" if any or all of the following conditions apply:
It was written using a language or methodology that is a generation behind current standards
The code is a complete mess with no planning or design behind it
It is written in outdated languages and in an outdated, non object-oriented style
It is difficult to find developers who know the language because it is so old
Unlike some of the other opinions here, I've seen plenty of modern applications that work decently without unit tests. Unit testing still has not caught on with everyone. Perhaps ten years from now the next generation of programmers will look at our current applications and consider them "legacy" for not containing unit tests, just as I consider non object-oriented applications to be legacy.
If few changes need to be made to a legacy codebase, it's better to simply leave it as-is and go with the flow. If the application needs drastic functionality changes, a GUI overhaul, and/or you can't find anyone who knows the programming language, it's time to throw away and start over. A word of warning, however: rewriting from scratch can be very time-consuming, and it's difficult to know if you've replicated all functionality. You'll probably want to have test cases and unit tests written for the legacy application and the new application.
Quite honestly legacy code is any code, framework, api, of other software construct thta's not "cool" anymore. For example COBOL is unanimously regarded as legacy while APL is not. Now one can also make the case that COBOL is consideed legacy and APL not because it has about 1m times the install base as APL. However, if you say that you need to work on APL code the reply would not be "oh no, that legacy stuff" but rather "oh my god, guess you won't be doing anything for the next century" see the difference?
This is a general term thrown around quite often (and quite generically) in the software ecosystem.
Well, I like to think of legacy code as inherited code. This is simply code that was written in the past. In most cases, legacy code do not follow new/current practices and is often considered archaic.
Legacy code is anything written more than a month ago :-)
It's often any code that isn't written in the trendy scripting language du jour, and I'm only half joking.
Stacker Nobody asked about the most shocking thing new programmers find as they enter the field.
Very high on the list, is the impact of inheriting a codebase with which one must rapidly become acquainted. It can be quite a shock to suddenly find yourself charged with maintaining N lines of code that has been clobbered together for who knows how long, and to have a short time in which to start contributing to it.
How do you efficiently absorb all this new data? What eases this transition? Is the only real solution to have already contributed to enough open-source projects that the shock wears off?
This also applies to veteran programmers. What techniques do you use to ease the transition into a new codebase?
I added the Community-Building tag to this because I'd also like to hear some war-stories about these transitions. Feel free to share how you handled a particularly stressful learning curve.
Pencil & Notebook ( don't get distracted trying to create a unrequested solution)
Make notes as you go and take an hour every monday to read thru and arrange the notes from previous weeks
with large codebases first impressions can be deceiving and issues tend to rearrange themselves rapidly while you are familiarizing yourself.
Remember the issues from your last work environment aren't necessarily valid or germane in your new environment. Beware of preconceived notions.
The notes/observations you make will help you learn quickly what questions to ask and of whom.
Hopefully you've been gathering the names of all the official (and unofficial) stakeholders.
One of the best ways to familiarize yourself with inherited code is to get your hands dirty. Start with fixing a few simple bugs and work your way into more complex ones. That will warm you up to the code better than trying to systematically review the code.
If there's a requirements or functional specification document (which is hopefully up-to-date), you must read it.
If there's a high-level or detailed design document (which is hopefully up-to-date), you probably should read it.
Another good way is to arrange a "transfer of information" session with the people who are familiar with the code, where they provide a presentation of the high level design and also do a walk-through of important/tricky parts of the code.
Write unit tests. You'll find the warts quicker, and you'll be more confident when the time comes to change the code.
Try to understand the business logic behind the code. Once you know why the code was written in the first place and what it is supposed to do, you can start reading through it, or as someone said, prolly fixing a few bugs here and there
My steps would be:
1.) Setup a source insight( or any good source code browser you use) workspace/project with all the source, header files, in the code base. Browsly at a higher level from the top most function(main) to lowermost function. During this code browsing, keep making notes on a paper/or a word document tracing the flow of the function calls. Do not get into function implementation nitti-gritties in this step, keep that for a later iterations. In this step keep track of what arguments are passed on to functions, return values, how the arguments that are passed to functions are initialized how the value of those arguments set modified, how the return values are used ?
2.) After one iteration of step 1.) after which you have some level of code and data structures used in the code base, setup a MSVC (or any other relevant compiler project according to the programming language of the code base), compile the code, execute with a valid test case, and single step through the code again from main till the last level of function. In between the function calls keep moting the values of variables passed, returned, various code paths taken, various code paths avoided, etc.
3.) Keep repeating 1.) and 2.) in iteratively till you are comfortable up to a point that you can change some code/add some code/find a bug in exisitng code/fix the bug!
-AD
I don't know about this being "the best way", but something I did at a recent job was to write a code spider/parser (in Ruby) that went through and built a call tree (and a reverse call tree) which I could later query. This was slightly non-trivial because we had PHP which called Perl which called SQL functions/procedures. Any other code-crawling tools would help in a similar fashion (i.e. javadoc, rdoc, perldoc, Doxygen etc.).
Reading any unit tests or specs can be quite enlightening.
Documenting things helps (either for yourself, or for other teammates, current and future). Read any existing documentation.
Of course, don't underestimate the power of simply asking a fellow teammate (or your boss!) questions. Early on, I asked as often as necessary "do we have a function/script/foo that does X?"
Go over the core libraries and read the function declarations. If it's C/C++, this means only the headers. Document whatever you don't understand.
The last time I did this, one of the comments I inserted was "This class is never used".
Do try to understand the code by fixing bugs in it. Do correct or maintain documentation. Don't modify comments in the code itself, that risks introducing new bugs.
In our line of work, generally speaking we do no changes to production code without good reason. This includes cosmetic changes; even these can introduce bugs.
No matter how disgusting a section of code seems, don't be tempted to rewrite it unless you have a bugfix or other change to do. If you spot a bug (or possible bug) when reading the code trying to learn it, record the bug for later triage, but don't attempt to fix it.
Another Procedure...
After reading Andy Hunt's "Pragmatic Thinking and Learning - Refactor Your Wetware" (which doesn't address this directly), I picked up a few tips that may be worth mentioning:
Observe Behavior:
If there's a UI, all the better. Use the app and get a mental map of relationships (e.g. links, modals, etc). Look at HTTP request if it helps, but don't put too much emphasis on it -- you just want a light, friendly acquaintance with app.
Acknowledge the Folder Structure:
Once again, this is light. Just see what belongs where, and hope that the structure is semantic enough -- you can always get some top-level information from here.
Analyze Call-Stacks, Top-Down:
Go through and list on paper or some other medium, but try not to type it -- this gets different parts of your brain engaged (build it out of Legos if you have to) -- function-calls, Objects, and variables that are closest to top-level first. Look at constants and modules, make sure you don't dive into fine-grained features if you can help it.
MindMap It!:
Maybe the most important step. Create a very rough draft mapping of your current understanding of the code. Make sure you run through the mindmap quickly. This allows an even spread of different parts of your brain to (mostly R-Mode) to have a say in the map.
Create clouds, boxes, etc. Wherever you initially think they should go on the paper. Feel free to denote boxes with syntactic symbols (e.g. 'F'-Function, 'f'-closure, 'C'-Constant, 'V'-Global Var, 'v'-low-level var, etc). Use arrows: Incoming array for arguments, Outgoing for returns, or what comes more naturally to you.
Start drawing connections to denote relationships. Its ok if it looks messy - this is a first draft.
Make a quick rough revision. Its its too hard to read, do another quick organization of it, but don't do more than one revision.
Open the Debugger:
Validate or invalidate any notions you had after the mapping. Track variables, arguments, returns, etc.
Track HTTP requests etc to get an idea of where the data is coming from. Look at the headers themselves but don't dive into the details of the request body.
MindMap Again!:
Now you should have a decent idea of most of the top-level functionality.
Create a new MindMap that has anything you missed in the first one. You can take more time with this one and even add some relatively small details -- but don't be afraid of what previous notions they may conflict with.
Compare this map with your last one and eliminate any question you had before, jot down new questions, and jot down conflicting perspectives.
Revise this map if its too hazy. Revise as much as you want, but keep revisions to a minimum.
Pretend Its Not Code:
If you can put it into mechanical terms, do so. The most important part of this is to come up with a metaphor for the app's behavior and/or smaller parts of the code. Think of ridiculous things, seriously. If it was an animal, a monster, a star, a robot. What kind would it be. If it was in Star Trek, what would they use it for. Think of many things to weigh it against.
Synthesis over Analysis:
Now you want to see not 'what' but 'how'. Any low-level parts that through you for a loop could be taken out and put into a sterile environment (you control its inputs). What sort of outputs are you getting. Is the system more complex than you originally thought? Simpler? Does it need improvements?
Contribute Something, Dude!:
Write a test, fix a bug, comment it, abstract it. You should have enough ability to start making minor contributions and FAILING IS OK :)! Note on any changes you made in commits, chat, email. If you did something dastardly, you guys can catch it before it goes to production -- if something is wrong, its a great way to get a teammate to clear things up for you. Usually listening to a teammate talk will clear a lot up that made your MindMaps clash.
In a nutshell, the most important thing to do is use a top-down fashion of getting as many different parts of your brain engaged as possible. It may even help to close your laptop and face your seat out the window if possible. Studies have shown that enforcing a deadline creates a "Pressure Hangover" for ~2.5 days after the deadline, which is why deadlines are often best to have on a Friday. So, BE RELAXED, THERE'S NO TIMECRUNCH, AND NOW PROVIDE YOURSELF WITH AN ENVIRONMENT THAT'S SAFE TO FAIL IN. Most of this can be fairly rushed through until you get down to details. Make sure that you don't bypass understanding of high-level topics.
Hope this helps you as well :)
All really good answers here. Just wanted to add few more things:
One can pair architectural understanding with flash cards and re-visiting those can solidify understanding. I find questions such as "Which part of code does X functionality ?", where X could be a useful functionality in your code base.
I also like to open a buffer in emacs and start re-writing some parts of the code base that I want to familiarize myself with and add my own comments etc.
One thing vi and emacs users can do is use tags. Tags are contained in a file ( usually called TAGS ). You generate one or more tags files by a command ( etags for emacs vtags for vi ). Then we you edit source code and you see a confusing function or variable you load the tags file and it will take you to where the function is declared ( not perfect by good enough ). I've actually written some macros that let you navigate source using Alt-cursor,
sort of like popd and pushd in many flavors of UNIX.
BubbaT
The first thing I do before going down into code is to use the application (as several different users, if necessary) to understand all the functionalities and see how they connect (how information flows inside the application).
After that I examine the framework in which the application was built, so that I can make a direct relationship between all the interfaces I have just seen with some View or UI code.
Then I look at the database and any database commands handling layer (if applicable), to understand how that information (which users manipulate) is stored and how it goes to and comes from the application
Finally, after learning where data comes from and how it is displayed I look at the business logic layer to see how data gets transformed.
I believe every application architecture can de divided like this and knowning the overall function (a who is who in your application) might be beneficial before really debugging it or adding new stuff - that is, if you have enough time to do so.
And yes, it also helps a lot to talk with someone who developed the current version of the software. However, if he/she is going to leave the company soon, keep a note on his/her wish list (what they wanted to do for the project but were unable to because of budget contraints).
create documentation for each thing you figured out from the codebase.
find out how it works by exprimentation - changing a few lines here and there and see what happens.
use geany as it speeds up the searching of commonly used variables and functions in the program and adds it to autocomplete.
find out if you can contact the orignal developers of the code base, through facebook or through googling for them.
find out the original purpose of the code and see if the code still fits that purpose or should be rewritten from scratch, in fulfillment of the intended purpose.
find out what frameworks did the code use, what editors did they use to produce the code.
the easiest way to deduce how a code works is by actually replicating how a certain part would have been done by you and rechecking the code if there is such a part.
it's reverse engineering - figuring out something by just trying to reengineer the solution.
most computer programmers have experience in coding, and there are certain patterns that you could look up if that's present in the code.
there are two types of code, object oriented and structurally oriented.
if you know how to do both, you're good to go, but if you aren't familiar with one or the other, you'd have to relearn how to program in that fashion to understand why it was coded that way.
in objected oriented code, you can easily create diagrams documenting the behaviors and methods of each object class.
if it's structurally oriented, meaning by function, create a functions list documenting what each function does and where it appears in the code..
i haven't done either of the above myself, as i'm a web developer it is relatively easy to figure out starting from index.php to the rest of the other pages how something works.
goodluck.