Last summers box office hit "snakes on a plane" was the unlikely story of
a batch of snakes getting loose in flight on a 747. In what some might
view as just as unlikely, ITA Software is using the Python language to
empower its airline reservation system.

Many computer language purists say that languages such as Java, C++ or C
should be used for enterprise applications. However, ITA, a Cambridge,
Mass., provider of airline IT software and services, is proving that
dynamic languages such as Python can be rock-solid for enterprise work.

Indeed, ITA in September 2006 announced an agreement with Montreal-based
Air Canada, a subsidiary of ACE Aviation Holdings, to develop a new
reservation management system for the airline. Air Canadas next-
generation reservation system will include reservations, inventory
control and seat availability, along with airport check-in and airport
operations modules.

Sean Menke, Air Canadas executive vice president and chief commercial
officer, said the new system "will be a key instrument in Air Canadas
strategy to maintain market leadership through product and customer
differentiation. Moreover, it will provide unprecedented flexibility and
significant cost savings."

Leaving Legacy Behind

Dan Kelley, director of application integration at ITA, said ITA will
deliver the system to Air Canada next year, and it will be deployed
across the entire Air Canada network, including reservation call centers
and airport locations throughout the world.

The reservation system will be delivered as an application hosted by ITA
Software.

ITA Software was founded in 1996 by computer scientists from the
Massachusetts Institute of Technology. The company provides airlines and
travel distribution companies with airfare pricing, shopping and
availability management systems and other technology.

ITA Softwares customers include Air Canada, Alaska Airlines, Alitalia,
Continental Airlines, US Airways, Star Alliance, Galileo International,
Kayak, Orbitz and others.

Like many of ITAs customers, Kayak.com, a comparison-shopping Web site
for airfares, uses ITA Softwares QPX airfare pricing and shopping system.
Unlike the traditional mainframe-based systems empowering most airline
software systems, QPX uses large numbers of commodity Linux-based PCs and
employs a component-based architecture that has no single point of
failure and that scales linearly.

"What ITA did historically is we did search," Kelley said. "Think of us
as Google for airfares. So if somebody like Orbitz, who is a customer of
ours, used us, theyd write a bunch of Java code that displays their Web
sites and does their front end. And they write a bunch of code that
actually does reservations on one of the big mainframes that maintains
the information about who bought what ticket. And the only thing we were
providing was search."

However, ITAs contract with Air Canada will have the company pulling Air
Canadas systems off the mainframe and onto a farm of Linux PCs.

"With Air Canada right now, were building an airline reservation system
that is going to replace their mainframe-based system, which does 95
percent of what they do as a business," Kelley said.

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"When you go and you check in on a kiosk at an airport, or you check a
bag, or buy a ticket through a travel agent or Web site, youre talking to
this one mainframe that right now sits in Winnipeg, [Manitoba]."

Instead of one monolithic system, ITA is writing a series of components
that are all going to be Linux processes running on different machines.
Kelleys unit is taking a group of 30 to 50 components and combining them
into a cohesive operating environment. Some of the key components are
written in Python. The Air Canada system has 110 interfaces, or ways that
people can interact with the system.

"And its hooked up to like 500 different computers here and elsewhere,"
Kelley said.

Yet, "in addition to being a huge technical challenge, nobody in the
history of airline computing has ever swapped out a mainframe-based
reservation system for something else," he said.

"Thats the scary thing for us. Sometime in the next year Air Canada is
going to turn off for a few hours, and then were going to turn back on
[using] the new system. That type of thing has never been done—going from
a legacy system to a new system."

Dynamic Python

Much of the code ITA employs is written in Python, despite skepticism by
some that dynamic languages are not ready for prime time. However, people
such as Guido van Rossum, the creator of Python, point to the successful
use of the language at places such as Google and YouTube, which endure
enterprise-scale traffic on a daily basis.

Meanwhile, ITA has about 200,000 lines of Python code in use in its
production software.

ITA has implemented a reliable multicast transport with congestion
control in order to deliver multiple streams of data, Kelley said. The
server is a mixture of C++ and Python, running on top of the Twisted
Python framework.

"In addition, some of the data feeds we receive from our customers and
partners are handled by network servers running on Twisted," Kelley said.

ITA has worked closely with its airline partners to build high-
performance servers to compute seat availability, Kelley said. Their
servers aggregate data from public and private data sources, including
both streaming and file-based data.

Each server requires a unique set of data feeds, and all the data feeds
must be monitored to ensure the data arrives when expected and gets
loaded as required, all while ensuring that system performance is not
impacted by these data management tasks. ITA uses Python to automate all
these tasks to make its systems reliable, easy to maintain and easy to
update as its customers needs change, Kelley said.

Moreover, ITA uses a Python application to monitor its heterogeneous
production environment that contains hundreds of servers.

"In order to do this efficiently, we developed our own monitoring
framework that enables the requirements to be expressed in configuration
rather than in code," Kelley said.

And ITA uses agile development methods, "which require that our software
is always buildable," he said.

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"To do this, we need to be able to perform automated regression tests
with every build, but our systems require dynamically changing data for
meaningful tests. ITA has built regression frameworks in Python to test
both availability and reservations systems. This framework enables us to
load test data while we test and has been built around a configuration
language so that it is straightforward to add new test cases as needed."

The first piece of core software ITA built using Python was a software
load balancer, Kelley said.

"We knew we needed a software load balancer to meet a customer commitment
to have their site up and running," he said.

"We had this hacked-together version that somebody had written in Perl in
a week, but it fell over continuously. And we needed something that we
could put together that would replace it but that also would be
maintainable over the long run." Python answered the call.

"Since then, weve changed how we use Python a ton internally," Kelley
said. "We have lots more production software written in Python. We've
basically reimplemented all our production service monitoring in Python
and also our production software management infrastructure for a
significant amount of what we run.

"A big component to that has been our use of Twisted Python. Were pretty
reliant on the Twisted framework, and we use it for our base-line
management software that we use to run the great majority of production
services that we have, our monitoring infrastructure and the next-
generation thing that we have coming, which is a suite of programs that
will automate the upgrade process for us," Kelley said.

A Mix of Components

The Air Canada system will be a mix of components written in different
languages, Kelley said.

"There are components written in Java, LISP, C++ and Python. For each
component area, we got a functional spec from the customer saying it has
to do X, and we had to figure out who the right people were to work on
that project, and those people decide what implementation language to
use," he said.

There are two critical components that are written in Python, without
which the system couldnt exist, Kelley said. The first is the inventory
controller, which keeps track of what seats are available on what planes.

However, "we think of the most core [component] as the piece that takes
reservation requests and records them in a database," Kelley said. "Thats
written in LISP. But the next most critical thing is the thing thats
maintaining inventory levels on airplanes, and thats written in Python."

The other core component is written in Python and is all "messaging well
do with travel agents and other reservation systems. That messaging
daemon is written in Python," Kelley said.

In addition, a significant percentage of Air Canadas ticket volume was
done through travel agents last year, he said. In the new system, every
one of those transactions will go through a Python message route.

But why Python?

"Historically, its not known for being something that somebody would go
out and code enterprise software in," Kelley said. However, "its
definitely an enterprise-caliber language in terms of stability,
scalability [and] the ability to have a large number of people work
together on a project.

"But its just coming into its own where you could defend it to
nontechnical people as a language on which you could develop enterprise
software. One of the things we have going for us is, because were founded
by computer scientists, we dont have to defend our use of that
programming language because its not Java," Kelley said.

"We have a wonderful ability here to choose the right tool for the job.
We have components that are written in Java, in C++, in Python, and Ruby
and Perl. [Python is] definitely viewed internally here by some of the
best computer scientists in the world, people from MITs AI [artificial
intelligence] and CS [computer science] labs, as enterprise worthy," he
said.

Indeed, ITA has to defend its ability to meet its SLA (service-level
agreements) against the Python-based technology.

"So we think, absolutely, that its ready for prime time," Kelley said.
"What were doing is saying to a billion-dollar business, Yes, we can
write components in this particular programming language, and they will
keep your airline running."

Adrian Holovaty, a developer at Washingtonpost.com and the creator of
Django, a Python Web development framework, bristles at the criticism of
Python as possibly not being ready for the enterprise.

"The word enterprise in this context is mostly meaningless to me," said
Holovaty in Chicago. "Its really just a marketing word that has no basis
in logic."

Holovaty pointed to Google and YouTube, saying that it "doesnt get much
higher traffic than that. Personally, I have direct experience using
Python as my primary development language daily at my day job at
Washingtonpost.com. Its a fantastic language that I couldnt live
without," he said.

Moreover, when ITA hires new people, the company likes to hire those with
Python experience "because weve had a lot of luck with Python people
having a lot of core problem-solving and system-building ability," Kelley
said.

He said it is pretty easy to find Java or C programmers who are good at
line coding but not generally good at problem solving. "Its much more
unusual for us to find people who can analyze a problem domain and then
implement a solution where they cross a bunch of problem domains," Kelley
said.

Python developers typically can, he said.

Meanwhile, getting off the mainframe will afford Air Canada all kinds of
productivity and cost benefits, including lower cost of maintenance,
better ability to integrate with modern architectures, and the ability to
add components and enhancements more easily than with the mainframe,
Kelley said.

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