Git Talk at the STL JUG

Yesterday (Oct. 9, 2008), I gave a talk on Git at the St. Louis Java User Group. Rather than a typical “intro” talk, instead I showed a dozen or so common usage scenarios, then answered questions with additional ad-hoc demos. As with some other recent talks, I eschewed PowerPoint in favor of a printed handout. The text of the handout follows below, or you can download the PDF. I also recorded the audio of the talk, but without video, so the general discussion portions are worthwhile but the demo portions are not.
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Please, Use a Web Application Framework

Historically I have not been a fan of “frameworks”, and I have often repeated the following joke:

What’s the difference between an application and a framework?

An application is something a customer actually wants!

However, for some applications, I recommend use of an application framework. For some Oasis Digital projects, I require it:

Please, Use a Web Application Framework

My reasoning here applies specifically to web applications with many CRUD (create-read-update-delete) features, and an underlying database. The advice applies much more widely, and with many nuances and caveats, but this article I am discussing only CRUD-ish web applications. Even within this niche, my reasoning does not apply to web applications which “push the envelope” of what is possible or which attempt to advance the state of the art.

Regardless of the programming language, the application should be built on a framework. More specifically, the framework should popular and mainstream, with a community of developers, and the appearance of momentum for the future. Likewise, the client-side JavaScript used in these applications, should also be based on such a framework. Here are some examples:

Ruby: Ruby on Rails, IOWA

Python: Django, TurboGears, Pylons, TwistedWeb

PHP: Akelos, CakePHP, CodeIgnitor, Symfony, Zend

Java: Struts, Seam, Rife, Tapestry, Stripes, Wicket Spring MVC

JavaScript: Scriptaculous, Prototype, JQuery

This is just a list of some frameworks that I am aware of; I have not evaluated all of these in detail, and I do not endorse them; nor is this an exhaustive list. For Oasis Digital projects, we help evaluate proposed frameworks, then I personally give the go-ahead to use a particular framework for a particular project.

An in-house web application framework does not meet the “community of developers” criteria, except at the very largest firms. Everywhere else, you are better off with an off-the-shelf, popular framework than with an inhouse framework, even if the latter is brilliantly designed.

Justification

My recommendation (and requirement, for some projects) for using an application framework for this kind of application is not based on a fad. Rather it is based on my years of experience as a developer, a team leader, a maintainer, and most importantly, a customer of software development.

The wild success of some frameworks (such as Ruby on Rails) has shown that they can reduce the amount of code and time needed to develop an application. That second factor, the amount of code specific to the application, is at least as important as the development time. Lines of code are not an asset; they are a liability. Only the features that the code provides are an asset. The most valuable software provides a lot of features using the smallest possible amount of application-specific code.

Therefore, even if a developer is so extraordinarily fast that they can create a system very quickly without using an off-the-shelf framework, they still have provided less value by doing so, compared to creating that same system quickly with fewer lines of code.

Another benefit of using a common framework (not a custom, in-house framework) is that this makes an application much easier and faster for other developers are work on in the future. A more maintainable system is more valuable.

Framework Caveats

Vidar Hokstad left a lengthy and excellent comment below, disagreeing with my thesis. It turns out that I mostly agree with Vidar, and it sounds like he and I have been through many of the same experiences with poor application frameworks. There are a lot of things an application framework can do wrong, and sadly, many of them take the opportunity to do so. In-house frameworks created by “architecture astronauts” seems to be especially prone to these defects:

  • All-or-nothing: Some frameworks intentionally or accidentally make it hard to replace a section of the framework. Don’t use these. Use a framework instead that has a “library” philosophy, such that you are readily choose to use some parts but not others.
  • Just Different: There are frameworks which offer an API wrapper around the underlying mechanisms, which isn’t really any better, just different. In this case, different is worse. Writing to (for example) the com.acme.inhouse.servlet API is, all else equal, much worse than writing to the standard Java Servlet API. To be worth its weight, a framework API must be demonstrably and obviously more concise.
  • Lower Abstraction: There are frameworks which, ironically, lower the level of abstraction of the application code, because that code ends up working around the framework features to get the job done.
  • Pile of Pieces: There are frameworks in which it is necessary to shred your application in to a pile of pieces, and then wire those pieces together with configuration files. This is sometimes useful, but often makes the application harder to understand, not easier, especially if there are extensive “XML pushups” involved. (I’m looking at YOU, Struts!) Instead, choose a framework with convention-over-configuration, and one which offers but does not require manual wiring.
  • Keyhole Database Access: If you find you mostly use a frameworks’ DB access features, and as a result you have short, easy to change code, then keep it. But if you find you use extensive SQL to work around lots of framework issues, throw it out. If a framework intentionally makes it hard to reach to the underlying SQL access, throw it out now.
  • No Source: If someone proposes a framework for which you won’t have source code, laugh. Aloud. If this gets you fired, then it has set you on a path to find employment at a more enlightened organization.
  • Exceptionally Bad Exception Handling: Java frameworks are especially prone to issues with exception handling, in which the framework code “eats” exception details.

In summary, pick up a framework and use it to get your application up and running quickly, but don’t be stupid. Do what makes sense locally for your project over time. It is a win to use an application framework to reach “1.0” functionality, even if you end up removing or swapping out parts of it later.

Is Delphi Dead? No.

A few months ago Alex Miller pointed me to this Delphi doom article (the site appears to be down at the moment), which reminded me to post about the same topic. Here goes.

Delphi shipped in 1995, and its demise has been declared frequently since 1997 or so. In a sense this demise is true, yet also false. Delphi’s current popularity is very different in form (not only in magnitude) from that of Java, C#, etc. Delphi is used substantially by commercial software vendors, and only rarely by enterprises. An ugly reality of the software industry is that the bulk of software developers nationwide work inside large non-software companies, so this usage pattern most likely does not produce the level of unit sales that Codegear (Borland’s dev-tools subsidiary) would like to see. It does, however, produce an enormous number of Delphi application instances running “in the field”, used by real paying end users, who don’t care (or know) what development tools were used to build the software they buy. Many commercial software products, both those in shrinkwrap at retail stores and those for vertical markets, are written in Delphi and will continue to be, because there are very few other good choices for high quality (polished) native Win32 GUI software. In these markets, shipping a Java or .NET app can be a competitive disadvantage (though to a lesser extent over time), and old-style VB is a sad joke.

I don’t think Delphi is eligible for demise until the dominant desktop operating system ships with a dominant runtime platform “in the box”. For example, if all of this happens at the same time:

  • Microsoft ships Windows with the .NET runtime already installed
  • That version Windows is the commonly deployed version
  • That version of the .NET runtime is the commonly targeted version

At that time, the .NET platform (with the language of your choice) could be a compelling replacement for Delphi in its niche. There is a lot to like about .NET (and Java, and I use them both), but I’m not holding my breath for the above conjunction.

Over at Oasis Digital we have several ongoing Delphi projects in which we develop and extend in-house, enterprise applications. These projects feel notably lonely (very few developers here in the midwest use Delphi), and the Delphi language leaves a lot to be desired (such as garbage collection) – but the resulting software works very well for our customers, especially when we add in a bit of Lua or Prolog (story coming someday…).

Delphi is not dead. It’s not at the top of the popularity charts, and won’t be. It probably shouldn’t be your first choice for a new in-house enterprise application starting today, because of the network effects of Java and .NET popularity. But Delphi is not going away anytime soon, and is a great choice for certain classes of projects.

Optimize Hierarchy Queries with a Transitive Closure Table

Last year I posted about the use of a Joe Celko-style nested set hierarchy representation, for fast hierarchy queries. Here I will describe another approach which is simpler to query, but more wasteful of space. I did not invent this transitive closure approach, I learned of it from several directions:

There are two (main) places to put the code for building a closure tables: in your application code, or in your database. The application approach is nice if you are aiming to avoid vendor-specific SQL code, but it is quite simple in SQL, and therefore not a big problem to recode for another RDBMS if the need arises. The SQL approach also avoids round-tripping the relevant data in and out of the database. Therefore, the approach I generally recommend for this is an SQL stored procedure / function.

Here is a simplified PostgreSQL stored procedure to do the job; note that his assumes a “widget” table with a widget_id and parent_id (the “adjacency” representation of a hierarchy), and a widget_closure table with fields (ancestor_id, widget_id, depth):

This sample code assumes a maximum depth of 20, and has no error checking. It will blindly miss greater depths and produce garbage if there is a “loop” in the ancestry. I recommend both arbitrary depth handling and error checking for production use.

Once your transitive closure table is populated, querying it is extremely fast and simple. You can get all the descendants of widget 12345 with the query “select widget_id from widget_closure where ancestor_id=12345”. Of course, this hierarchy representation, while simple to generate, is not simple to incrementally update as the hierarchy changes. The most straightforward way to use it is as a cache, regenerated as needed.

Growing a Language, by Guy Steele

This is an oldie-but-goodie: Guy Steele’s “Growing a Language” talk from OOPSLA 1998.

It is amazing to me that Guy, whose is something of a legend in language design, and who thinks so clearly about what makes a good language, was also key in designing Java. Java has been extremely slow to grow in the sense described in this talk, because for many years Sun resisted such growth. Only the rise of C# and the growing popularity of dynamic languages generated enough pressure to get Java unstuck… and in the last few year Java has become somewhat growable in the sense Guy describes.

Next Big Language = JavaScript

There’s a lot of buzz about Steve Yegge’s “port” of Rails to JavaScript, and Steve has now provided (in his funny, self-deprecating style) the background of how it came to be. He doesn’t quite say it explicitly in this post, but I think it reveals that the “Next Big Language” he has been hinting at is JavaScript.

I (mostly) agree:

JavaScript is in nearly every browser, including tiny ones (like the one in my BlackBerry Pearl). It may be the single most widely available language today.

Because of the above, an enormous population of JavaScript programmers (though sometimes of dubious skill) has emerged.

Starting with Java 6 it’s “in the box” there also. To me, this makes it the likely winner, by a wide margin, for a dynamic language to be used at Java shops or inside Java projects. Being “in the box” is a powerful advantage, one which the many other contenders will have a hard time overcoming.

Adobe’s new JavaScript virtual machine implementation, which they handed over to Mozilla as “Tamarin”, sounds like it will boost JavaScript performance great, making it good enough for a very wide variety of projects.

JavasScript uses curly braces, like the last few Big Languages.

Like Java, C, C++, etc., JavaScript has specs and multiple competing, complete, current, high quality implementations. This, to me, is a big advantage over Ruby, Python, and other currently popular dynamic languages. Of course there is plenty of room in the industry for these language to thrive also, I am not saying any of them will go away; we use Python with great results and expect to keep doing so.
Mark Volkmann initially thought I was nuts to predict JavaScript as a winner but came around a few month later (and said so in a user group talk).

In a project at work, we’d adopted JavaScript as our plugin extension language for user-customizable rules (billing rules, etc.). I’d have chosen Lua (as I did for another project), but there are at least 1000x as many JavaScript programs out there. So far it has worked very well. If we had it to do over we might implement far more of the project in JavaScript.

However, there are a few reasons why I only “mostly” agree:

First, with JavaScript there isn’t a good way to avoid shipping source code. Sure, you an obfuscate JavaScript with various tools, but the results remains far for amenable to readable-source recovery than in a more traditionally compiled language. For open source projects this is no big deal, but there are also many worthwhile businesses and projects which depend on proprietary, not open software (including most of our projects), and it’s not year clear that obfuscation is sufficient protection. (Update in reply to a comment below: This matters even for server-side software, because some of us create and sell software products for other people to run on their servers.)

Second, at the moment JavaScript appears to lack a module system, without which it’s painful to build large systems. I expect an upcoming language version will address this.