Software Development with Open Source

Software Development with "
Open Source

Jon Allen (JJ) – jj@opusvl.com
Birmingham University 2010

Software Development with Open Source
Open Source Business Systems
www.opusvl.com

About OpusVL

•  Open Source development company
•  Based in Rugby, UK

•  Founded in 2000
•  Business systems (ERP, VOIP, CRM, etc)
•  Bespoke software development
•  Use and contribute to Open Source
–  Code
–  Sponsorship
www.opusvl.com

Open Source

•  Who uses Open Source software?

www.opusvl.com

Open Source


•  Who uses…
–  Google
–  Facebook
–  BBC iPlayer
–  Amazon

www.opusvl.com

Open Source


•  Who uses…
–  Google
–  Facebook
–  BBC iPlayer
–  Amazon

•  All built on Open Source software

www.opusvl.com

What is Open Source Software?

•  Licensing model
–  Free redistribution
–  Source code available
–  Modiﬁcations and derived works allowed
•  Distribution allowed under same terms as original licence
–  No discrimination against people or ﬁelds of usage

•  Typical licenses
–  BSD, Apache, GPL, Artistic
•  Restrictions vary by license (BSD vs. Copyleft)

www.opusvl.com

Why Open Source?

•  Try before you buy
–  Use ﬁrst, get support later
–  Open documentation, support forums, etc
•  Source code available
–  Can make changes and ﬁx bugs
•  Freedom to fork
–  No vendor lock-in
•  Access to developers
–  Speak directly to the author

www.opusvl.com

What do we use?

•  Products
–  Debian, Ubuntu, Apache, PostgreSQL, CouchDB,
Asterisk, XEN, OpenERP, DAViCal, Memcached, etc.

•  Development tools
–  Perl
–  Catalyst, Moose, DBIx::Class, Template Toolkit,
DateTime, HTML::FormFu, etc.

www.opusvl.com

Perl

•  Multi-paradigm programming language
–  Procedural, Functional, Object-Oriented
•  Mature, stable, scalable
–  Used in mission-critical systems across the globe
–  BBC, Cisco, Amazon, Vodafone, LOVEFiLM
–  http://www.perl.org

•  Perl 5, version 12.2
–  Released 7th September 2010

www.opusvl.com

CPAN

•  Comprehensive Perl Archive Network
–  Over 21,000 modules - Perl’s “killer app”

•  Interfaces, frameworks, applications, dev tools, ﬁle
formats, imaging, databases, and lots more
•  Code reuse
–  Don’t re-invent the wheel
–  Building blocks for applications
•  http://search.cpan.org

www.opusvl.com

Quality Assurance

•  Perl has a strong QA culture
•  Test-driven development

•  CPAN Testers
–  Automated testing community
–  Every CPAN upload tested with multiple platforms
and Perl versions
–  9,000,000 test reports (500,000 per month)
–  http://www.cpantesters.org

www.opusvl.com

Community

•  Perl Mongers – local user groups
–  Birmingham, London, Milton Keynes, North West
–  http://birmingham.pm.org
•  Conferences and workshops
–  YAPC – Europe, Asia, Russia, North America
–  http://conferences.yapceurope.org/lpw2010
•  Online
–  http://blogs.perl.org
–  Forums, IRC, mailing lists

www.opusvl.com

Jobs

•  Contribute to Open Source projects
–  Very impressive on your CV
–  Great way to gain experience
•  Not just programming
–  Documentation, testing, bug triage

•  User groups
–  Perl Mongers, LUGs, UKUUG, Multipack, PyWM
–  Networking – get yourself known

www.opusvl.com

Software Stack

Client customisations •  Core framework
–  Catalyst
Client OpusVL
application
components
application
components
–  Moose
–  DBIx::Class
OpusVL framework modules

DBMS
Core framework modules Ingres,
Catalyst, Moose, DBIx::Class, etc PostgreSQL,
CouchDB, etc

Base software stack
Linux, Apache, Perl

www.opusvl.com

DBIx::Class

•  ORM – Object Relational Mapper
–  Database abstraction layer

•  Creates objects, classes, and methods
•  Writes SQL – improves maintainability
•  Easily add new class methods
–  Business logic
–  Encapsulation
•  Use methods, not database queries

www.opusvl.com

DBIx::Class Schema

•  Describes tables and relationships
–  Loaded from DB – DBIx::Class::Schema::Loader
CREATE TABLE authors (
id integer primary key,
name text
);
CREATE TABLE books (
id integer primary key,
author_id integer,
title text,
foreign key(author_id) references authors(id)
);

dbicdump Authors 'dbi:SQLite:test.db'

www.opusvl.com

Using generated classes

•  Gives us an Authors class
–  Relationships converted to class methods
use Authors;
my $db = Authors->connect("dbi:SQLite:test.db");

my $author = $db->resultset("Author")
->find(name => "Stephen King");

foreach my $book ($author->books) {
say $book->title;
say $book->author->name;
}

www.opusvl.com

Extending classes

•  With a “rate” method added to the Book class
# in Authors/Result/Author.pm

use List::Utils qw/sum/;

sub is_liked {
my $self = shift;

my $total = sum(
map {$_->rating} $self->books->all
);

return ($total / $self->books->count) > 3;
}

www.opusvl.com

Moose

•  Object Oriented programming framework

•  Extension of Perl’s native OO
•  Improves syntax and facilities
–  Method modiﬁers, introspection, roles, type checking
•  Large developer community

•  http://moose.perl.org

www.opusvl.com

Moose example

use MooseX::Declare

class Report extends ‘Document’
with ‘Confidentiality’ {

has ‘total’ => (isa => ‘Num’, default => ‘1000’);
has ‘notes’ => (isa => ‘Str’);

method fake_data {...}
}

role Confidentiality {
before print {
# hide any incriminating data!
};
}

www.opusvl.com

Catalyst

•  Web development framework

•  Application server
•  Scalable, high performance
–  Powers some of the world’s biggest websites
•  Structured, maintainable
–  URLs dispatched to class methods
•  DRY – Don’t Repeat Yourself
–  Modular, self-contained components

www.opusvl.com

What does Catalyst provide?

•  Session handling
•  Authentication / access control
•  Page caching
•  Built-in development server
•  URL generation
–  What’s the URL to reach this method?

•  Library of pre-built components

www.opusvl.com

Catalyst block diagram

View

Stash
User Controller

Model

Business Logic DB

www.opusvl.com

Model

•  Business logic

•  Interface to a class
–  Data storage (DBIx::Class, LDAP, S3, data ﬁles)
–  API (REST, SOAP, XMLRPC)
–  External system (OpenERP, Asterisk, hardware)
–  Any other piece of Perl code
•  External to Catalyst
–  Used and maintained separately

www.opusvl.com

View

•  Presentation logic

•  Renders output as…
–  HTML, XML, JSON, PDF, Excel, JPEG, PNG, etc.
–  Template::Toolkit
•  Messaging
–  Email, SMS
•  Processing
–  Generating thumbnail images

www.opusvl.com

Controller

•  Application logic
–  Links Models to Views

•  Passes input to the model
•  Puts data from the model onto the stash
•  Runs the application
–  Control ﬂow
–  Logging / error handling
–  Status codes

www.opusvl.com

Conclusion

•  Open Source gives us the tools to deliver
•  The Community makes it possible

•  Birmingham Perl Mongers
–  http://birmingham.pm.org
•  Birmingham Linux User Group
–  http://birmingham.lug.org.uk

www.opusvl.com

Essay question

•  Open Source software is often perceived as being non-
commercial as free redistribution is permitted. However,
many companies have managed to turn both the
development and usage of Open Source software into a
proﬁtable business.

–  Research the different business models that companies use
to derive commercial beneﬁt from Open Source software.

–  Investigate the challenges that companies face in managing
external development and user communities.

www.opusvl.com

Software Development with Open Source

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