Monthly Archives: July 2010

OSCON 2010: License to Fail

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Robert “r0ml” Lefkowitz

This session is a companion to the session on competition r0ml presented on Wednesday. For those of us who, for whatever reason, were unable to attend the previous session, he provided us with five second summaries:

  • Wednesday: Competition is bad, don’t do it.
  • Thursday: Licensing is bad, don’t do it.

And with that, the session is over.

I’m kidding, of course. The best part of any of r0ml’s talks is the logic he uses to get from his observation to his conclusion. As he noted at the outset, the path typically takes us through the Middle Ages.

I don’t deal with lawyers very much in my day job, since I work in a support role for our engineering departments. However, I know several people in our Open Source group, and have attempted to release some of the Perl modules I’ve written while on the job. Doing so is decidedly non-trivial and, after two years I still haven’t been allowed to release my code. To say I’m disappointed is an understatement.

My experience with lawyers has been that they are extremely cautious. While frustrating, I understand that it’s their job to play it safe and to protect the company. They are scared, almost beyond reason, that an Open Source license will find its way into a piece of intellectual property that they’d rather not release. It can’t be easy trying to bridge the gap between the closed and open ways of doing business.

The topic was introduced with a question: What is the difference between copyright and plagiarism? Plagiarism is forever. I didn’t quite catch what r0ml meant by this, but I suspect it means that copyright (eventually) expires, granting the work in question to the public domain. Plagiarism, if one can get away with it, creates an attribution that lasts forever.

That, if one is an Open Source geek, leads one to think about licenses. Let’s take the attribution clause of the BSD, which contains two sub-clauses, for example. It’s redundant. It effectively means that the recipient of the source code can not claim credit for the author’s work. Under copyright law, this is already the case, so why the redundancy.

In the name of efficiency and refactoring, r0ml mused whether it would be possible to reduce the number of license clauses to one. He found this in the Do What The Fuck You Want To Public License.

Through inductive reasoning, if we can reduce the number of clauses from two to one, we should be able to similarly reduce the number of clauses from one to zero. After all, if we begin with the earlier premise that licenses are bad, this should be the goal, right?

First, briefly, why are licenses bad? There are many reasons and many arguments; too many of each for this post, but to summarize a few important ones, as of this writing, the Open Source Initiative lists 73 approved licenses. Choosing between them can be a daunting task. Neither do all of these licenses play well with each other, further complicating the selection task if one is attempting to integrate differently-licensed source code. Finally, it’s rare that anyone knows all that they are agreeing to in the license.

The Medieval sensibility was that all knowledge came either from God or from the Ancients. As such, no one could claim credit for a work, because, without exception, it would be plagiarism. For this reason, the majority of works produced during the Middle Ages were compilations, a representation of existing information.

We have a modern equivalent of this Medieval concept of copyright, called the Compilation Copyright. A compilation of files in the public domain is assembled with copyright only on the compilation. Further, no one may claim credit on the same collection of files. Instead, a new compilation, or derivative work, must be created.

How bad has copyright gotten? Well, thanks to the Apple development kit, there is a short piece of code, included in every project, that is separately copyrighted by everyone who has used the development kit. This is getting out of hand, to say the least.

So r0ml wrote unlicense.rb, which will scan a directory recursively, removing any licenses it finds. This, of course, is perfectly acceptable under the terms of the licenses being removed, so long as the files aren’t redistributed. It does have the effect of pleasing the obsessive-compulsive user.

Under the laws of many countries, a copyright notice isn’t actually required to have a copyright. This is particularly true in the United States and the European Union. In fact, in the latter one cannot even waive the protections of copyright. This creates the default case: without a license, nobody other than the author has the right to do anything with the code. The default is all rights reserved.

Richard Stallman, founder of the GNU project and the Free Software Foundation, was not trying to protect the author of code from people downloading the code; rather, he created the GNU General Public License to protect the users of the code. He felt that users have an inherent right to have access to the code running on their computer. Thus, the primary reason for the creation of Open Source licenses was to protect the user.

Many companies claim that they have an Open Source business model. Typically what this means is that they offer their software, or some subset of their software for free, under an Open Source license. Then they offer support contracts, for usually high prices. These aren’t really Open Source business models. The SQLite project has the only known true Open Source business model. The software itself is released into the public domain. This is a scary place for lawyers, especially those employed by large companies. To assuage their concerns, the company that employs the author of SQLite will be more than happy to sell them an Open Source license for the code.

Next, r0ml talked about warranties. In some jurisdictions, the default case under the law is that there is an implied warranty, unless stated otherwise. Most of us have seen the disclaimer of warranty, included to protect the author, attached to the license in code we have downloaded (or added it to code we’ve released), usually in all capital letters. While not a strict requirement to be in capital letters, it is a requirement that the disclaimer be made to stand out. Often, licenses are in plain text files, so using a bold face type isn’t possible. Hence, capital letters. The simplest case of a disclaimer is such:

/* This program comes without any warranty, to the extent permitted by law. */

As we recall, the default case under the law is an implied warranty so including the phrase “to the extent permitted by law” is redundant. Also, it should be noted that copyright law, in the United States, is codified at the Federal level, in Title 17 of the United States Code, while warranty law is codified by the states. This leads to many more jurisdictions, and far more potential confusion, for warranty law.

So finally, here is r0ml’s part serious, part humorous take away: don’t include either a copyright or a warranty with your code. If a user sues you for damages under the implied warranty in a state court, counter-sue them in US federal court for copyright infringement. After all, under the law they were not given permission to copy the code anyway.

A question came at the end of the session, from someone who appeared mildly upset and defensive. He pointed out that Stallman created the GNU General Public License for a good reason, which wasn’t mentioned by r0ml during his talk. Someone had taken the code Stallman was freely distributing and sold it. After which, they went back to Stallman to inform him that he could no longer distribute his own code, because he hadn’t licensed it. The questioner appeared to be offended by the whole point of the session, apparently feeling that all the work Stallman has done for Free Software was being ridiculed and that, without these licenses, “capitalists” will simply steal the code for their own nefarious purposes.

To this, r0ml did have a response. Copyright law has changed since Stallman faced the problem that led to his creation of Free Software. It has become more strict and the requirement for registration has been dropped. The point was made that the questioner is actually referring to the concept of provenance, not copyright. However, this concept was not further explored as, unfortunately, time had run out.

OSCON 2010: Friday Morning Plenary Sessions

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I’m tired this morning after a long week at OSCON, so my ability to understand and summarize the Friday plenary sessions is diminished. As such, what follows won’t be terribly useful to anyone.

Your Work in Open Source, 3 years of Incremental Change

Chris DiBona (Google, Inc.)

Google crawled 40 million files in Google Code to generate statistics on what’s in there. Lines of code and numbers of commits are not the most useful of metrics but that’s what they have to use.

The Gnu General Public License is the most used license, at over 50%. Of those, more than half have moved to GPL version 3. Perl has declined a bit, but C has the most use, at about 40%.

Many companies are committing code, too.

Mayor Sam Adams

Sam Adams (City of Portland, Oregon)

Last September, Portland adopted one of the first Open Source policies in the nation. They’ve committed themselves to open software, open data, and Open Source in the procurement process for software.

It’s pretty cool when a politician gets it.

Situation Normal, Everything Must Change

Simon Wardley (Leading Edge Forum (CSC))

Simon started with a recap of the talk he gave last year, which showed correlations between the ubiquity and certainty. All technologies follow the same curve, from having both low ubiquity and certainty up to having both high ubiquity and certainty. The stages tend to be the innovation of a technology, the productization, and finally the comoditization.

The basic idea was that the cloud, as it is known, is still in its infancy. As it matures, we will see innovations built on it at an accelerated rate. If we don’t pay attention to it, we’ll be left behind.

Well defined processes stifle innovation.

Projects or teams can be organized by lifecycle: innovation, leverage, and commoditize. This circles back on itself. When one thing is commoditized, a new innovation can be built on top of it.

OSCON 2010: State of the Onion

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The Thursday sessions are over, but before I head out to the parties, I’m attending the 14th State of the Onion address. This is the always well-attended update on the universe of Perl. I immediately noticed that Larry is surrounded by his wife and his son, the former dressed as an angel, the latter as a devil.

Larry claims that so rarely does he talk about Perl in the States of the Onion addresses that he has brought his conscience with him today to prod him in the right direction (the aforementioned angel and devil).

The current state of the onion is segmented into left, central, and right sections. It can be labeled, say, 5 and 6. They can also be labeled 0 and 1, for false and true. Larry then asked a series of boolean questions, asking the audience to weigh in on the veracity.

Do you think Perl 5 and Perl 6 are really the same language?

Do you think Perl 5 and Perl 6 are really different languages?

As the angel and the devil argued, Larry pointed out that an important skill for a language designer is to be able to stay on the fence long enough until he can determine which side the grass is greener on. Sometimes you discover that you’re sitting on the wrong fence and the voices in your head start to argue about which side has the greener grass.

When the voices in your head start arguing if the purple cow eats greener grass than the brown fence, it’s time to see a doctor. Or find a better drug dealer.

— Larry Wall

This is, of course, a metaphor for being a language designer. Sometimes you sit on the fence for language features, without ever knowing which direction is the better one.

Next up is a live demo of Perl 6; or, more specifically, of Rakudo Star, which is scheduled to be released next week. Some of the demos, without comment:

.say if 6 %% $_ for 1..^6
[+] gather { take $_ if 6 %% $_ for 1..^6 }
[+] grep { 6 %% $_ }, 1..^6
~[+] grep 6 %% *, 1..^6
-> $n { $n == [+] grep $n %% *,  ..^ $n }
-> $n { $n == [+] grep $n %% *,  ..^ $n }(6)

At this point, the examples scrolled off the screen due to a “whatever” example being run. That’s good news, though. It means Rakudo Star supports lazy lists and, as such, we finally have those infinite lists we’ve been promised:

0, 1, ... *

The whatever star can, in addition to being used as in an infinite series, can be used to curry a function:

(1, 1, *+* ... *)[^20]    # Fibbonacci
(0, !* ... *)[^20]        # 0 1 0 1 0 1 ...

In a recent video interview, Larry was asked, if he were hit by a bus, has he designated anyone to be his successor as the leader of the Perl 6 project? His response was that he trusts the Perl community to choose the right person.

Onions can make you cry, so can disruptive technologies or innovations. Almost everyone has labeled their technology as disruptive. As such, the phrase has lost most of its meaning.

A disruptive technology simultaneously does something worse and does something better than its competitors. In a time of the Unix philosophy of “do one thing and do it well,” Perl came along and attempted to do everything, but didn’t necessarily do any of it well. The Unix philosophy was broken by its own utilities. No one knew what a “thing” was, and no utility of the time did it well. By the time Perl 4 turned into Perl 5, it demonstrated that a tool that was itself an entire tool shed could run circles around shell scripts.

In California, we once had many, many colonies of ants. Now, most of California is populated by a single colony of Argentine ants. This is because the colonies have forgotten how to fight with each other. Perl 6 has benefited from multiple teams creating multiple implementations, in the end working together to create a better product, even if that product takes longer to complete.

If you don’t like Camelia, you can just fork off.

— Larry Wall

The takeaway, I think: It is up to all of us to determine what Perl 6 will be. What kind of disruptive technology will it be?

OSCON 2010: Awesome Things You’ve Missed in Perl

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Paul Fenwick (Perl Training Australia)

Ever since I saw An Illustrated History of Failure two years ago, I’ve made it a point to see @pjf‘s talks. That’s how I find myself in his mid-afternoon session, Awesome Things You’ve Missed in Perl. Judging by the size of the crowd, I’m not the only one. However, I won’t attempt to pass along his humour in this post. I’d never do it justice.

In his introduction, Piers Cawley asked that we go wild when Paul took the stage, so the folks in the Google Wave session next door would be taken aback, and realize that Perl is not, in fact, dead.

People are still out there writing Perl as if still in the dark ages of 2008. Paul doesn’t want us to write old Perl, but only new and shiny Perl. This talk only covers practices that have come about since Perl Best Practices was released.

Object-oriented Perl is not awesome. Not even close. If you look at the old ways of doing it, all of them are either wrong, stupid, or both. The rest are too hard. There’s a simple way to fix this: use Moose. This module does so much of the infrastructure work of composing classes, it makes object-oriented programming enjoyable again.

Paul spent a lot of time giving a humorous, high-level overview of the features available in Moose.

The Moose module contains a huge number of extension modules in the MooseX namespace.

When I have a problem, I go down to the pub with other Perl mongers and bitch.

One of the limitations of Perl, that is exposed to Moose, is that not everything is an object. This means methods like push() or isa() can’t be called on everything. And checking types defeats the purpose of polymorphism. Enter the autobox module, which turns everything into an object. As a bonus, it operates in lexical scope. Moose exposes autobox through the Moose::Autobox module.

A module that Paul wrote, autodie, which is now included in core. This lexically scoped module removes all of the boilerplate code that goes along with trapping errors from subroutines.

Not only is Perl 5.10 awesome, but Perl 5.10 regular expressions are awesome. In particular, the introduction of named captures (via %+) made regular expressions extremely awesome.

Perl 5.10 also provides grammars in the regular expression engine. This is the basis for Damian Conway’s Regexp::Grammars module.

Referring to an article on SweeperBot in The Perl Review. However, there’s the problem of distributing a program that uses half of CPAN to users of inferior operating systems, such as Microsoft Windows. That’s where the PAR module comes in. It will pack up all of the modules used by the program, including the Perl interpreter itself if necessary, so a single, self-reliant file can be distributed to users who need it.

Remember to never optimize code. Programmer time is far more valuable than CPU time. However, when you must optimize code, profile first. The Devel::NYTProf makes profiling awesome.

Code reviews are important, but Perl programmers are lazy. Fortunately, the Perl::Critic module has read Perl Best Practices for you and will complain about where your code violates the practices in the book. At my day job, it does about half the work of code reviews for me, loudly announcing violations of the coding standards that I enforce with an iron fist.

If you find an awesome module, buy the author a beer if you have the opportunity. There’s also CPAN Ratings to leave feedback or perlthanks in recent versions of Perl.

OSCON 2010: 21st Century Systems Perl

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Matt Trout (Shadowcat Systems Limited)

The full title of this session is, 21st Century Systems Perl – the New Perl Enlightment for sysadmins

Introduction

While Perl isn’t dying, “PERL” most certainly is dying. This is a good thing, because it includes all the really crappy stuff, such as Matt’s Script Archive. Thank goodness for that. To be fair, this code would have been horrible written in any language. Remember, blame the artist, not the tool.

We have a very mature community, which means we also have very mature practices. We are also converging on a standard platform, even if there are more than one ways to do something.

Part 1: Minimising Developer Fatalities

As a developer, we should do what we can to make our sysadmins’ lives easier.

Right off the bat, we should use the local::lib module, which allows an application to use custom library areas without polluting the system installation areas. It can even work with /etc/skel. Matt is a big fan of using a local library path, included with the application, so it can be maintained separately from both the operating system vendor’s modules and even other applications.

Improve module installation using Module::Install.

Package modules for your distribution of choice using cpan2dist.

Improve the CPAN experience using App::cpanminus, which is amazing easy to bootstrap:

> wget cpanmin.us
> ./cpanm

Start using all of the modules associated with best practices by installing Task::Kensho.

Vendors are getting better at distributing Perl and keeping up with module releases. The Debian Perl team is the strongest, with Fedora lagging quite a bit far behind. Fedora is finally getting better, now that members of the Perl community have a say in the packaging of Perl and the modules.

After many debug sessions, Matt has come to the conclusion that mod_$lang is evil. Jamming languages into the web server is a bad, bad idea. However, actually hooking into the different handlers can be useful. Matt’s preference now is now FastCGI.

Part 2: Maximising Automation Banality

“In the systems world, shiny and exciting is not good.”

Use the autodie (in core as of 5.10) and the IPC::System::Simple modules to reduce the repetitiveness and the common errors of systems programming.

Use IO::All to fix the syntax and semantics of I/O operations.

Systems script shouldn’t need to be deployed. It should be possible to just drop the script onto a host and it will Just Work. That’s where PAR::Packer.

OSCON 2010: Dist::Zilla

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Ricardo Signes (Pobox.com)

The full title of this talk is, Dist::Zilla – Maximum Overkill for CPAN Distributions.

Every CPAN distribution contains a significant amount of crap. It’s infrastructure used for the distribution tools.

ExtUtils::MakeMaker has been the traditional way to work on the infrastructure code. By necessity, it contains a lot of legacy, which can be cumbersome to maintain. Enter Module::Install, which can look in the expected places for the necessary information, such as the author name. But, the author still must write all the boilerplate. Module::Starter was written to address this, composing all the boilerplate on behalf of the author. There is so much boilerplate that, by default, Module::Starter also provides a boilerplate test to detect it.

Why are we doing all of this? How much repetitive work are we doing?

What can Dist::Zilla do for us? For starters, we can remove some files:

  • LICENSE
  • MANIFEST.SKIP
  • Makefile.PL
  • README
  • t/pod.t
  • t/pod-coverage.t

Leaving us with only our Changes file, our code, and our tests. The non-infrastructure parts. On top of that, Dist::Zilla does all of the boring distribution bits for us. It only handles the make dist command. It does not handle the make install command, which means the users who install the module don’t need all of the dependencies.

Dist::Zilla puts all of its functionality into plugins, which will be the meat of the rest of this session. It also uses a very simple INI-style configuration file.

The main command provided by the module is dzil build. This bundles the distribution, which will contain all of the infrastructure necessary for users to install the module. When building, it follows a simple work flow:

  1. Gather files
  2. Munge files
  3. Collect metadata
  4. Write out

There is no default configuration, but there is a Basic plugin bundle that will include all of the most common plugins.

What followed were examples of what the plugins can do. Of course, all of them are designed to reduce cruft—the non-code, non-documentation bits that we’re forced to maintain. The philosophy is the same one I advocate to anyone who will listen: computers are good at doing boring, repetitive tasks with derived data; why don’t we let them do more of that stuff?

I’ve followed @rjbs on Twitter for a while, and I’ve seen him talk about Dist::Zilla. I’ve wanted to try it out for a while, to simplify my distributions—both for CPAN and for my day job—but I didn’t realize until this session just how awesome the tool is. It’s a complete framework for managing Perl module distributions. Dist::Zilla will give my Laziness score a huge bump.

OSCON 2010: Thursday Plenary Session

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This morning’s plenary session, based on the scheduled speakers, is focused on the nebulous cloud. The cloud is what everyone in technology talks about, but everyone defines differently. It’s the section of the flow chart where magic happens. Somehow, we will send our data into the cloud and all our wishes will be fulfilled.

To be fair, this vagueness and my pessimism are precisely why these speakers have been invited to the O’Reilly Open Source Convention. Tim O’Reilly has a grand vision for the cloud, for ubiquitous computing, and the use of technology to help solve the world’s problems. I commend him for that. I hope this morning’s speakers do justice to his vision and that, if there are valuable lessons to be learned, that we learn them.

Today’s LAMP Stack

David Recordon (Facebook)

Over the last decade, the LAMP stack hasn’t been fundamentally updated. A cache, such as memcached has been added. Different languages (Perl, Python, Ruby) have been used in place of the original PHP. Even different web servers have been used in place of Apache.

Facebook created HipHop for PHP, which compiles PHP into C++. Creating native executables in this way reduces CPU use by a large factor (a number I didn’t catch).

There are alternatives for the database component in the stack, too. MySQL is ubiquitous at this point. Facebook doesn’t really use the relational bits of MySQL very much. So they have been using databases from the NoSQL family—Hadoop, according to the presentation.

David made a point I think a lot of people miss. When evaluating databases, or any other software, first look at what problem needs solving, then find a product that solves it in the correct way. Too often I see people advocating their preferred solution without even looking at the problem.

Data is the lifeblood of Facebook (and we all have our own opinions about that). They are able to use a plethora of Open Source tools to store the data, scale the data, and analyze the data.

This talk wasn’t very focused on the cloud, aside from Facebook being a nebulous site where people store their data without really knowing where it goes or how it’s used. I expect this was more for public relations, given all the bad press they’ve had. Not that anyone stops using Facebook.

Open SETIQuest – It Will Be What You Make It!

Jill Tarter (SETI Institute)

Jill started her talk by explaining what SETI is and why it exists, which I won’t go into here, since it’s just a Google search away. I used to run SETI@home a bit over a decade ago when I was in college and felt like using my computer as a space heater.

Jill is here, representing SETI, because she wants to involve the world in their search. SETI has classroom materials covered, but they are lacking in the social networking world. Jill wants people to first identify themselves as Earthlings, recognizing our place in the Universe.

SETI, with the development of the setiQuest community, hopes to use the vast resources available in the Open Source world to improve the project. These include physical resources, such as cloud storage and compute cycles, to human resources, such as programmers and analysts.

Cloudant has created a SETI stack on the Amazon AWS infrastructure.

Open Cloud, Open Data

Jean Paoli (Microsoft)

I’m always a little concerned when I see a speaker from Microsoft at OSCON. While I can imagine that there are employees at the company who genuinely embrace Open Source—and, presumably from this talk, open data—I can’t lay aside my suspicion. Microsoft does not have a benevolent history with competition, so when a representative shows up to talk about an open cloud with open data, I instinctively look for the company’s angle. What is their nefarious plan?

Jean talked about open standards and open data. Data portability, standards, easy migration and deployment, and developer choice. For some reason, when he talks about the “open cloud,” I have thoughts about Microsoft’s OpenDocument move a few years ago. Sure, parts of it were open, but the format as a whole was useless for non-Microsoft tools.

He claimed that Microsoft Windows Azure is an open and interoperable platform. I have a hard time swallowing that. The #oscon IRC channel was not kind in its commentary. A selection from the channel logs:

<b3gl> "Microsoft totally agrees..." as long as you pay your Windows, Azure and MSSQL license fees

<alapapa> standards are great…as long as they're ours

<dbrewer> wow, thanks Microsoft.  You think I should be able to use any language I want, I appreciate your permissions.

<b3gl> dbrewer: Notice he didn't say "We believe if you want to use Linux ...."

Public Static Void

Rob Pike (Google, Inc.)

Programming languages used to be relatively simple, but still fairly powerful. They’ve gotten considerably more complex and confusing. The C++ language was used as an easy target during the talk. Rob went on to bash various (in most cases deservedly) programming languages as a way to lead into what he called the renaissance of language design.

Many of the emerging languages are dynamic and interpreted, and there’s a false dichotomy that they are considered good while the static and compiled languages are considered bad. Part of the problem is that the latter class of languages are old, designed in a different age of computing.

Obviously, the end goal of this talk was to talk about the Go language, which tries to bridge the gap between the dynamic interpreted languages and the static compiled languages.

Toward an Open Cloud

Lew Moorman (Rackspace.com)

Lew’s talk was to introduce OpenStack. Rackspace took the internal software that powers their cloud and donated it to OpenStack. I wonder if this is something we can use at my day job to build an internal cloud. The stack is licensed under the Apache 2 license and they don’t use a dual licensing model, which sounds nice.

I was wrong, the talks weren’t really about demonstrating the wonder of ubiquitous computing and how we can move in that direction so much as a showcase of organizations in the cloud or using the cloud. It was really just one long commercial.

OSCON 2010: Hands-on Cassandra

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The second tutorial I attended on Tuesday, and the last one of the conference, was Hands-on Cassandra. Actually, I missed the first half of this tutorial, for reasons which I explain in my Tuesday recap post.

I’ve been told by those that attended the full tutorial that the first half wasn’t really worth attending. In fact, when I arrived at the beginning of the second half, I caught the tail end of the presenter demonstrating how he recreated Twitter using Cassandra, something he dubbed Twissandra. This seems to be the exercise of choice for any distributed system. In a way, that’s smart. Take a highly distributed system everyone is familiar with, explain the challenges faced by such a system, then demonstrate the effectiveness with which the software in question can solve the problem.

In any case, the second half of the tutorial was mostly dedicated to an explanation of how Cassandra distributes its data. The details and, frankly, the delivery weren’t that interesting for me, so I didn’t follow the discussion. It was too high level to keep my interest.

I still think that Cassandra is deserving of some investigation. I have a project in mind that it may be perfect for. At my day job, we have what is essentially a distributed, key-based data store. We’ve had to implement all of the data replication functionality. If Cassandra can alleviate the need to design and implement our own data replication and integrity systems, we can put more effort into the final delivery of the data, instead of its transmission.

OSCON 2010: Environmental Monitoring with Arduino

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Russell Nelson (Open Source Initiative)

For my final session of the day, I’m in Environmental Monitoring with Arduino and Compatibles. Since I attended the Arduino tutorial on Monday, I thought it would be fun to attend a session on using them.

The take-away points, presented up front for our convenience:

  • Environmental monitoring is important
  • Arduino is cheap and easy
  • Small computers are fun

The Arduino is not just the chip and board, but the IDE used to program the board. It also, as I learned on Monday, has a very shallow learning curve.

Russell works for a company doing water monitoring of the Hudson River. He’s using his domain knowledge from his job to explain how one would do something similar on a smaller scale. The values he describes detecting, and the circuits used to take the measurements, are,

  • Temperature
  • Turbidity
  • Salinity – can’t measure this directly, but salinity conducts and we can measure resistance

Now I just need to figure out what I want to monitor at home.

OSCON 2010: Smalltalk-style Traits

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Curtis “Ovid” Poe (BBC)

After a long break, an apple, a cup of coffee, and a beer, I’m back in the Perl track.

The full title of this session is, Scratching the 40-Year Itch of Inheritance with Smalltalk-style Traits.

This is not a tutorial. How to use traits is easy, but why to use them is a more complex discussion.

Inheritance is a very complex problem and an easy one to get wrong. Then people start doing things with multiple inheritance and, even if they’re not doing something deliberately stupid, they end up with diamond inheritance. Not only is this a problem, but it’s been a problem for a very long time—40 years, in fact.

Complex systems can lead to deep class hierarchies. When hierarchies are deep, in particular with a dynamic language like Perl, it becomes difficult to determine where a method came from. Even when its known where a method comes from, undesired behavior may be inherited. This becomes worse when multiple inheritance is used.

As systems grow, the problem becomes two-fold:

  1. Class responsibility – larger classes are desired
  2. Class reuse – smaller classes are desired

Inheritance, by itself, cannot solve this problem. So the solution is to
decouple the sub-problems.

Several solutions have been tried:

  • Interfaces
  • Delegation
  • Mixins – incredibly popular

As expected by the name of this session, traits (or roles in the nomenclature of Moose) solve the problem far better than any of the above solutions. Much of the session involved showing real-world application of roles to clean up code at the BBC.