DREXEL UNIVERSITY, ISCHOOL
INFO 630, DR. PETER GRILLO
SPRING QUARTER, 2011
Cleanroom Software Engineering
Stephenson, Chad
Due: June 6/7/2011
Table of Contents
INTRODUCTION ................................................................................................................................................. 3
BACKGROUND .................................................................................................................................................. 3
PRINCIPLES........................................................................................................................................................ 3
PROCESS ............................................................................................................................................................ 4
BOX OVERVIEW ................................................................................................................................................. 6
CONCLUSION: .................................................................................................................................................... 7
REFERENCES: ................................................................................................................................................... 8
CERTIFICATION ................................................................................................................................................. 9
INTRODUCTION
“Lets do it right the first time” This is the basic philosophy of cleanroom software engineering. It
is a process for developing high-quality software with certified reliability. “Cleanroom software
engineering is a theory based, team oriented process for development and certification of highreliability software systems under statistical quality control” (Linger, Richard). The purpose is
the development of software that has no failures in use. The name comes from hardware
cleanroom. The emphasis of Cleanroom approach is on a rigorous engineering discipline and the
focus is on defect prevention as opposed to defect removal. “The approach of cleanroom
combines mathematical based methods of software specification, design and correctness
verification with statistical, usage based testing to certify software fitness for use”. (Chetan and
Ying) What it comes down tom, is having a strong design from the beginning that has no or few
errors. Instead of developing software quickly then debugging, the Cleanroom approach is to
spend more time (and money) upfront to prevent errors after it is developed.
BACKGROUND
Development of the cleanroom software engineering process was by Harlan Mills and Alan
Hevner at IBM. It began its use in the mid 80s. Military use began in the early 90s. It has been
used in many cases where reliability is very important. It is kind of interesting that the name
Cleanroom would be used in software engineering. The use of the name came from the
electronics world where everything must be clean. If it is not defect could be introduced into
final products.
Cleanroom does not follow a common software development process of code it and fix it. So
instead of just writing the code, a programmer must design the code and algorithms by first fully
understanding what it is it needs to do. A lot of time and money is spent upfront to prevent errors
and issues later down the road. But that will later reduce the cost during development. This is
done partly by using statistical methods. Cleanroom stresses that the design is certified by
statistically testing and is mathematically correct. The main benefits of using Cleanroom
approach is zero failures in the field, shorter development cycles and it tends to result in longer
life of products.
PRINCIPLES
Cleanroom software engineering differs in that it is done using a box structured approach. It uses
a technology that is object based. These are a box method that include clear, state and black
boxes. (Chetan and Ying). Instead of saying that 100% of the project is 75% finished you would
say 75% of the project is 100% done. The basic principles of the Cleanroom process are as
follows,
1) Software development based on Mathematical Principles: Using mathematical functions
is one of the main principles of Cleanroom Software Engineering. This differs then other
traditional that are used such as the waterfall method. The Box Structured Method is
used in Cleanroom Software Engineering. Specification and Design is used by this
method. To insure that a design is a correct implementation of what is being specified,
Cleanroom uses functional verification. Before any line of code is ever executed,
correctness verification is done. This prevents developers to getting into debugging
mode.
2) Incremental implantation under statistical quality control: Instead of looking at the
project as a whole and finding errors from there, each state is looked. At. By using strict
standers each process (or iteration) is measured for quality. Each stage is looked at as a
whole. This is where the previous statement that x amount of the project is 100%
complete. The project cannot move forward unless the strict standards are met. If the
standards are not met, there must be a return to the design stage.
3) Software Development based on Statistical Principles: Statistics is used to try to figure
out all possible uses of the software. In other words, a “sample” is used to draw
conclusions about a “population.” Under a testing protocol that is faithful to the
principles of applied statistics, a scientifically valid statement can be made about the
expected operational performance of the software based on its test performance.” (Becker
& Borris)
PROCESS
Cleanroom engineering follows a specific approach and steps. They are broken down into
specification processes, development processes and certification process. They are as follows
Cleanroom Specification Process
1) Requirements analysis: It this state a project manager or team would produce and review
informal specifications. Finding out what the project/design needs to do and what needs
to be done to meet the final needs of the end users. Function, usage, environment and
performance would all be taken into consideration. After the requirements have been
gathered the next step is to figure out how to make it work. In this step the requirements
would be converted into state machines and functions
2) Function Specification: What is the software suppose to do. Everything about the
software including what it does, who it is for is specified. The customer must agree with
the function specification.
3) Usage Specification: In this process the use of the software is identified. In addition the
types of environments is also identified. Again this is another part of the certification
process and it must come with an agreement from the customer on the specified usage.
4) Architecure Specification: This process uses three key dimensions of architecture which
are conceptual, module and execution. The Black Box (later discussed) method is used.
5) Increment Process: The software architecture is put together in this phase by using
allocating the customer requirements that were provisory defined. In the incremental
process a schedule is defined and resources are allocated. “In the incremental process, a
software system grows from initial to final form through a series of increments that
implement user functions, execute in the system environment and accumulate into the
final system” (Linger & Trammell)
Cleanroom Development Processes
6) Software Reengineering: One benefit of the Cleanroom Process is that it can be used in
situations for software reuse where it was not previously used. The purpose is to prepare
reused software (which previously may not have been Cleanroom). When software is
going to be reused it must first be understood. It may be necessary to use correctness
verification during this process. Again certification is a necessary part of this phase.
7) Increment Design: Using the Cleanroom principles, code is designed. Mathematical
models . and box structure decomposition help to create the code that is going to be used.
Part of doing the box structure method is paralling the design and specification.
Increments are designed and implemented as usage hierarchies. If a software application
or design is going to be designed using cleanroom approach, compiling code or unit
testing would not be allowed. In this state code is developed and are verified using
informal methods. During high level design code is written in increments. After each
section test cases are generated.
8) Correctness Verification: Using mathematically based techniques the correctness of the
software is verified. “Black box specifications are verified to be complete, consistent,
and correct. State box specifications are verified with respect to black box specifications,
and clear box procedures are verified with respect to state box specifications. “ (Linger &
Trammell) Questions are asked and if necessary a change is made which requires
revivification. During verification results are validated by compiling code, linking it and
testing it.
Cleanroom Certification Processes
9) Usage Modling and Test Planning: This is another important part of the process that
requires customer agreement for certification. The creation of usage models are used for
testing of the software as well as defining test plans. Again statistics are used, in this
situation for testing.
10) Statistical Testing and Certification: The final state in verifying that the software is doing
what it is intended to do. Decision are made on whether to do further testing, to revisit
prior steps or to certify the software up to that point.
BOX OVERVIEW
Box Types
1) Black box - specifies a set of transition rules that describe the behavior of system
components as responses to specific stimuli. (Chetan & Ying). The black box hides data
implementation and process implementation. This is usually arranged into hierarchies
based on usage.
2)
State box – Within this box state machine are generalized. In addition objects may be
encapsulated. Basically it is showing data implementation. State box hides process
implementation.
3)
Clear box – Box becomes fully visible. Shows both data implementation and process
implementation. The clear box is fully a fully developed procedure.
The first step is to create the black box which is specified and validated. Within this system
boundaries are established. After mapping rules are created the owners and users must validate.
Second a state box is specified and validated. Because this is showing data implementation,
transition functions must be shown. Behaviors from the black box is derived.
Last is designing and verifying the clear box. Controls and operations are put into this box.
Figure1: Example of Black Box Method (Chetan
and Ying)
CONCLUSION:
Cleanroom is all about and stresses good design. Instead of just throwing something together and
finding out what’s wrong with it later, errors are prevented before, so you don’t have to fix them
later. A typical software lifecycle might include 40% design, 20%code and 40% testing (to find
the errors). With a cleanroom approach we might now say that it is 80% design and 20% coding
(testing sometimes not necessary because the finished product is error free). With cleanroom
errors are found in earlier stages thus reducing errors later down the road. With Cleanroom
Software Engineering, quality is achieved by design, not testing. It can also be used for new or
existing systems.
REFERENCES:
Kale, Chetan & Jin Ying (2004) Cleanroom Software Development,
Becker, Shirley & Beizer Borris; Cleanroom Software Engineering; Retrieved on 6/1/2011;
http://www.uta.edu/cse/levine/fall99/cse5324/cr/clean
CLEANROOM SOFTWARE ENGINEERING REFERENCE MODEL. VERSION 1.0. (n.d.).
Retrieved from http://quanterion.com/Documents/Documents.asp?ArgVal=708
Cleanroom Software Development. (n.d.). Retrieved from
http://www.khambatti.com/mujtaba/ArticlesAndPapers/Cleanroom%20Software%20Develo
pment.pdf
Cleanroom Software Engineering – Reference Model Version 1.0 by Richard C. Linger, Carmen
J. Trammell 1996
CERTIFICATION
I certify that: This assignment is entirely my own work.
I have not quoted the words of any other person from a printed source or a website without
indicating what has been quoted and providing an appropriate citation.
I have not submitted any of the material in this document to satisfy the requirements of any other
course.
Chad D Stephenson