Software Verification and Validation: An Engineering and Scientific Approach

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The usual definitions are: Validation: Are we building the right system? Verification: Are we building the system right? John Mueller October 5, at pm. Molly Levy August 8, at am. Omama September 21, at pm. Andre Paulino de Lima March 5, at pm. Repson January March 10, at am. Thanks for this article. This will be helpful in my final year project. Nirvanie Prashad April 2, at pm. Samia Shah May 25, at am. Mohamed Bile Super June 3, at pm. This is the best different of validation and verification so read care fully Thanks. Alice May 15, at am. Bhagya October 19, at am. Niranjan December 14, at am.

Mohan March 26, at pm. Hi there, Thanks for this very helpful article. Steve March 26, at pm. Sorry, we're experiencing some technical difficulties. Please try again. Download Features Overview. Explore the capabilities of a fully cloud-based CAE platform by creating a Community account or signing up for a day trial of the Professional plan Community plan day Professional Trial. Verification and Validation. Read Time 4 Minutes. Megan Jenkins September 12, Read Time 6 Minutes. Aisling Hughes September 4, Read Time 5 Minutes.

And yet, it's an all too common scenario in software companies today. When the software products being created are destined for embedded systems, the problem is exacerbated. When you burn control software onto a ROM, put it in a device, and ship it to millions of customers, you'd like to have a deeper sense of the innate quality of that software. Or when you put a team of astronauts onto a launch pad and trust their lives to the software controlling the on-board computers, you'd like to think it's going to work the first time.

Verification

Yes, you need to test. But the product you're testing must have been built with some level of quality in the first place, particularly when your product is an embedded system of some kind. This idea was well expressed by Boris Beizer, oddly enough or perhaps appropriately enough in a book about testing: "The single most important thing that can be done to achieve quality software is to design the quality in.

That's more important than how the quality assurance department is structured, who it reports to, what testing is independent, what kind of reviews are held-more important than the entire contents of this book, of Software Testing Techniques, and of the next ten books published on software quality assurance. So how do you determine whether quality was inherent in the design in the first place?

One important idea is to have an eye toward quality throughout the product life cycle, from requirements elicitation all the way to first customer ship.

To incorporate an attention to quality at each phase of software development requires a process to govern its application. Most software process improvement models such as CMM and ISO begin with an assumption that effective and appropriate processes naturally and inevitably lead to the production of high quality software. This assumption is derived from manufacturing systems where product quality is intimately related to the production process. As Peter Coffee stated, "Quality is not a feature that can be added to a current product: It is a process, one that begins with product design and continues long after the product is sold.

In the following sections, we will introduce basic principles of defect management, and then discuss verification and validation of software through the product life cycle. In particular we will discuss reviews, inspections, and testing as mechanisms for performing verification and validation. Defect management Software contains faults or defects, which are errors in software introduced by developers. These defects may have been introduced at virtually any point in the development process from requirements to maintenance. These defects may lay dormant if the proper circumstances never arise to force the problematic code into execution.

Or they may become evident as failures. Failures span a range of severity. In the worst case, the failures may take the form of system crashes or incorrect system functionality. In milder cases, failures may simply make users unhappy or dissatisfied such as slow response time or an interface that's difficult to use. Defects are to be avoided, of course.

Two guiding principles govern the management of defects. First, avoid introducing defects in the first place. That can be done by applying proper techniques at each step in the product life cycle. For example, many defects are actually introduced during requirements elicitation. And yet few software engineers have received any formal training in this important function.

By performing effective requirements elicitation, it's possible to avoid introducing a significant number of defects. The same can be said for every other phase in the product life cycle. We know that, despite our best efforts, defects will be introduced into our products. The second governing principle, then, is to detect defects as early in the process as possible. Once a defect has been detected, it needs to be removed at the source.

This means that if the defect was introduced during low-level design, it needs to be removed there-ideally before coding begins. If the defect was introduced during requirements elicitation, it needs to be removed there-ideally before high-level design begins. The longer we wait, the greater will be the cost involved in removing and repairing a defect. Studies have indicated that the cost of defect removal rises dramatically the later they are discovered in the product life cycle.

The focus of verification and validation is to detect defects as early as possible after they are introduced and remove them at the source. Doing so not only makes the removal of defects cheaper, it also provides a much stronger confidence that quality is being built into a product, rather than trying to filter it in just before shipping. Speaking broadly, validation is concerned with building the right product, and verification is concerned with building the product right. The following definitions may shed light on what we mean exactly by building the right product and building the product right.

Definition 1 Validation is the "determination of the correctness of the final program or software produced from a development project with respect to the user needs and requirements. Validation is usually accomplished by verifying each stage of the software development life cycle.

Verification is then concerned with the translation and traceability of each stage of development to its dependent stage. In other words, design can be shown to correctly derive from requirements. This definition makes the assumption that validation is commonly achieved through verification of each phase. Definition 2 "Verification involves evaluating software during each life-cycle phase to ensure that it meets the requirements set forth in the previous phase. Validation involves testing software or its specification at the end of the development effort to ensure that it meets its requirements that it does what it is supposed to.

We would suggest that this approach only works because they both begin with the letter V and thus can be conveniently bunched together.


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To do so is to lose a tremendous amount of the power inherent in the distinct focus of each. Verification refers to the set of activities that ensure that software correctly implements a specific function.

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Validation refers to a different set of activities that ensure that the software that has been built is traceable to customer requirements. The definition of validation is agreeable, but the definition of verification here is a bit too simplistic. There is more to verification than seeing that functions are implemented correctly.

Verification and Validation in Computer-Aided Engineering – Explained

In this article, we will use "validation" to refer to those activities that attempt to determine that customer needs can be met by a product. This may include usability testing or other types of user feedback. It may involve inspection of requirements documents or assessing whether requirements elicitation was performed effectively.

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It may also include testing of the final system with respect to the original user requirements to see that those requirements were met. Hence, validation helps to see that we are building the right product. We will use "verification" to refer to the transformational activities that are performed at each step of the product life cycle. In other words, from a user requirements specification, a high-level design can be made.

At the point that the design document is complete, it can be "verified" against the requirements document.

Verification and Validation in Software Quality Management

At this point, defects can be detected and corrected. This high-level design can then be used to verify the low-level design document that stems from it. This process of verification applies at each stage in the development process and can include essentially every document or artifact produced along the way, including in addition to the documents already mentioned source code, internal documentation, user documentation, test plans, and test specifications. The most common way to perform validation of a system is through testing. Few other options are available.

Besides, if you have an accurate requirements document and a functioning system, running it through its paces to see if it meets the defined requirements makes a great deal of sense. But how do you assess the quality of a document? That's not as straightforward. The easiest answer is, read it and talk about it. See if it's traceable to the document from which it was derived. This process is largely one of reviews and inspections. Reviews and inspections "Technical work needs reviewing for the same reason that pencils need erasers: to err is human.

For example, if software is being built without defined accurate requirements, it is essentially impossible to verify, via reviews or any other method, whether the design is accurate. Since the design is not based on requirements, it simply stands alone, and any assertion of defects ultimately devolves into a matter of personal opinion.

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So performing reviews and inspections presumes a certain level of rigor in the process being applied to the creation of the software in the first place. Reviewing the intermediate development artifacts at each stage of development has two primary values. First, we can detect defects early and remove them when the cost is relatively low. Second, and possibly more significant, we can influence the process within our company, forcing a greater amount of rigor in the creation of the software in the first place. If management buys off on the value of reviews, it will become immediately obvious that without good requirements or good design reviews won't bring much value.

Reviews typically involve a small group of people all looking at the same work product or development artifact. Why involve other people? For the same reason an author can skip past a typo in an article a dozen times, while a copy editor will see it more readily: we all have blind spots.

For some, the thought of bringing one's heretofore private work product under the scrutiny of a room full of people is disconcerting at best. It's not a pleasant experience to have one's baby dubbed ugly in a public setting. For that reason, the scope of these meetings should be limited to a handful of people, and all participants should be trained, so that negative repercussions can be avoided.

Reviews function as a form of quality filter that is applied at various points during software development. The motivation behind reviews is to uncover errors and purify work products as early as possible.

Verification

Specifically, reviews attempt to achieve the following outcomes: Point out needed improvements in the product. Confirm the parts that are good. Bring some consistency to the product in terms of coding style, document style, design approach, and so on, which makes the technical work more manageable. Improve the software development process. Reviews can span the spectrum of formalism, from extremely formal to very informal.

In the most formal settings, many people may participate although there are clearly points at which more participants will reduce effectiveness , tremendous corporate resources may be expended, and lots of photocopies are needed to keep everyone on the paper trail. On the other extreme, there are very informal gatherings that are reviews nonetheless.

These may involve just one or two people gathering in a cube, or in the hall. It may be as simple as a request for help from one engineer to another. In these informal meetings, few rules govern the meeting, diversions are common, and the group often jumps into problem solving mode. These kinds of gatherings can be very valuable under the right circumstances. We typically use inspection to refer to more formal meetings in which specific roles are played by participants, specific rules govern the meeting, and greater rigor is applied, particularly when involving the traceability of one work product to its predecessor.

Completeness means that a work product is complete with respect to its predecessor. This means that there are no items marked "TBD" to be determined , there are no non-existent references, no missing specification items particularly unconsidered special cases , no missing functions, and no missing products.

If a previous work product identifies a function or feature, then the work product being reviewed must have its analogous treatment of the same function or feature.

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