The Return of Ada
- By Joab Jackson
- April 14, 2008
Last fall, contractor Lockheed Martin delivered an update to the Federal Aviation
Administration's next-generation flight data air traffic control system
-- ahead of schedule and under budget, which is something you don't
often hear about in government circles.
The project, dubbed the En Route Automation Modernization System (ERAM), involved
writing more than 1.2 million lines of code and had been labeled by the Government
Accountability Office (GAO) as a high-risk effort. The GAO worried that many
bugs in the program would appear, which would delay operations and drive up
Although the project's success can be attributed to a lot of factors, Jeff
O'Leary, an FAA software development and acquisition manager who oversaw ERAM,
attributed at least part of it to the use of the Ada
programming language. About half the code in the system is Ada, according
to O'Leary, and it provided a controlled environment that allowed programmers
to develop secure, solid code.
Today, when most people refer to Ada, it's usually as a cautionary tale.
The Defense Department commissioned the programming language in the late 1970s.
The idea was that mandating its use across all the services would stem the
proliferation of many programming languages and even a greater number of dialects.
Despite the mandate, few programmers used Ada, and the mandate was dropped in
1997. Developers and engineers claimed it was difficult to use.
Military developers stuck with the venerable C programming language they knew
well, or they moved to the up-and-coming C++. A few years later, Java took hold,
However, Ada never vanished completely. In fact, in certain communities --
notably aviation software -- it has remained the programming language of choice.
"It's interesting that people think that Ada has gone away. In this industry,
there is a technology du jour. And people assume things disappear. But especially
in the Defense Department, nothing ever disappears," said Robert Dewar, president
of AdaCore and a
professor emeritus of computer science at New York University. Dewar has been
working with Ada since 1980.
Last fall, the faithful gathered at the annual SIGAda 2007 conference in Fairfax,
Va., where O'Leary and others spoke about Ada's promise.
This decades-old language can solve a few of today's most pressing problems
-- most notably security and reliability.
"We're seeing a resurgence of interest," Dewar said. "I
think people are beginning to realize that C++ is not the world's best
choice for critical code."
ERAM is the latest component in a multi-decade plan to upgrade the country's
air traffic control system. Not surprisingly, the system had some pretty stringent
development requirements, according to O'Leary.
The system could never lose data. It had to be fault-tolerant. It had to be
easily upgraded. It had to allow for continuous monitoring. Programs had to
be able to recover from a crash. And the code that runs the system must "be
provably and test-ably free" of errors, O'Leary said.
And such testing should reveal when errors occur and when the correct procedures
fail to occur. "If I get packet 218, but not 217, it would request 217
again," he said.
Ada can offer assistance to programmers with many of these tasks, even if it
does require more work on the part of the programmer.
"The thing people have always said about Ada is that it is hard to get
a program by the compiler, but once you did, it would always work," Dewar
said. "The compiler is checking a lot of stuff. Unlike a C program, where
the C compiler will accept pretty much anything and then you have to fight off
the bugs in the debugger, many of the problems in Ada are found by the compiler."
That stringency causes more work for programmers, but it will also make the
code more secure, Ada enthusiasts say.
When the DOD commissioned the language in 1977 from the French Bull Co., it
required that it have lots of checks to ensure the code did what the programmer
intended, and nothing more or less.
For instance, unlike many modern languages and even traditional ones such as
C and C++, Ada has a feature called strong typing. This means that for every
variable a programmer declares, he or she must also specify a range of all possible
inputs. If the range entered is 1-100, for instance, and the number 102 is entered,
then the program won't accept that data. This ensures that a malicious hacker
can't enter a long string of characters as part of a buffer overflow attack
or that a wrong value won't later crash the program.
Ada allows developers to prove security properties about programs. For instance,
a programmer might want to prove that a variable is not altered while it is
being used through the program. Ada is also friendly to static analysis tools.
Static analysis looks at the program flow to ensure odd things aren't taking
place -- such as making sure the program always calls a certain function with
the same number of arguments.
"There is nothing in C that stops a program from doing that," Dewar said. "In
Ada, it is impossible."
According to O'Leary, Ada was not perfect for the ERAM job. There are more
than a few things that are still needed. One is better analysis tools.
"We're not exploiting the data" to the full extent that it
could be used, he said. The component interfaces could be better. There should
also be tools for automatic code generation and better cross-language support.
Nonetheless, many observers believe the basics of Ada are in place for wider
Who uses Ada? Not surprisingly, the DOD still uses the language, particularly
for command and control systems, according to Dewar. About half of AdaCore's
sales are to the DOD. AdaCore offers an integrated developer environment called
GnatPro, and an Ada compiler.
"There [are] tens of millions of lines of Ada in Defense programs,"
NASA and avionics hardware manufacturers are also heavy users of Ada, he said.
Anything mission-critical would be suitable for Ada. For instance, embedded
systems in the Boeing 777 and 787 run Ada code. In all these cases, the component
manufacturers are "interested in highly reliable mission-critical programs.
And that is the niche that Ada has found its way into," Dewar said.
In addition to AdaCore, IBM Rational and Green Hills Software offer Ada developer
It also works well as a teaching language. The Air Force Academy found it to
be a good language that inexperienced programmers could use to build robust
programs. At the SigAda conference, instructor Leemon Baird III showed how a
student used Ada to build an artificial-intelligence function for a computer
to play a game called Connect4 against human opponents.
"A great part of his success was due to Ada's features,"
Although it was only 2,000 lines, the language allowed the student to write
"It had to be correct," he said. The code flowed easily between
Solaris and Windows, and could be run across different types of processors with
Programs written in an extension of Ada, called Spark, will be used to run
the next-generation U.K. ground station air traffic control system, called Interim
Future Area Control Tools Support (IFacts). Praxis, a U.K. systems engineering
company, is providing the operating code for IFacts.
In 2002, England's busiest airport terminal, London Heathrow Airport, suffered
a software-based breakdown of its airplane routing system. Praxis is under a
lot of pressure to ensure its code is free from defects.
Praxis also used Spark for a 2006 National Security Agency-funded project,
called the Tokeneer ID Station, said Rod Chapman, an engineer at Praxis. The
idea was to create software that would meet the Common Criteria requirements
for Evaluation Assurance Level 5, a process long thought to be too challenging
for commercial software.
To do this, the software code that was generated had to have a low number of
errors. The program itself was access control software. Someone wishing to gain
entry to a secure facility and use a workstation would need the proper smart
card and provide a fingerprint. By using Spark, a static check was made of the
software before it was run, to ensure all the possible conditions led to valid
outcomes. In more than 9,939 lines of code, no defects were found after the
testing and remediation process was completed.
Although the original language leaned heavily toward strong typing and provability,
subsequent iterations have kept Ada modernized, Dewar said. Ada 95 added object-oriented
programming capabilities, and Ada 2005 tamped down on security requirements
even further. The language has also been ratified as a standard by the American
National Standards Institute and by the International Organization of Standards
Incidentally, Ada was named for Augusta Ada King, Countess of Lovelace, daughter
of Lord Byron. In the early 19th century, she published what is considered by
most to be the world's first computer program, to be run on a prototype of a
computer designed by Charles Babbage, called the Analytical Engine. But don't
let the language's historical legacy fool you -- it might be just the thing
to answer tomorrow's security and reliability challenges.