Jillan Rose E. Gonzales
I.T. 16
BSIT IV-J
July 2, 2012 ASSIGNMENT
Explain the difference between errors, faults and failures. Give an example of an error that leads to a fault in the requirements: the design; the code. Give an example of fault in the requirements that leads to a failure; a fault in the design that leads to a failure; a fault in the test data that leads to a failure. A fault occurs when a human makes a mistake, called an error while failure is a departure from the system’s required behavior. A fault is an inside view of the system, as seen by the eyes of the developers, whereas a failure is an outside view: a problem that the user sees. For example, many software engineers think that an antiballistic-missile system would require at least 10million lines of codes; some estimates range as high as 100 million. By comparison, the software supporting the American space shuttle consists of 3million lines of codes, including computers on the ground controlling the launch and the flight; there were 100,000 lines of code in the shuttle itself. Thus, an antimissile software system would require the testing of an enormous amount of code.
Why can a count of faults be a misleading measure of product quality? A count of faults is misleading measure of product quality because there usually is not a one-to-one correspondence between faults and failures. If many faults are located in code that is never or rarely executed, then they are unlikely to result in many failures, which is usually a more relevant measure of quality. On the other hand, if just one fault is located in code that is exercised heavily in regular use, it could result in numerous failures, and thus low-quality software. Furthermore, neither a count of faults nor a count of failures gives an indication of the severity of the problems.
What are the legal and ethical implications of using COTS software? Of using subcontractors? For example, who is responsible for fixing the problem when the major system fails as a result of a fault in COTS software? Who is liable when such a failure causes harm to the users, directly( as when the automatic brakes fail in a car) or indirectly (as when the wrong information is supplied to another system, as we saw in Exercise 1). What checks and balances are needed to ensure the quality of COTS software before it is integrated into a larger system? The customer may decide to purchase Commercial Off-The-Shelf (COTS) software to be incorporated in the final product that the developer will supply and support. When this happen, the customers is involved system architecture decisions, and there are many more constraints on development. Developers work together with customers and users to define requirements and specify what the
proposed system will do. Suppose you are maintaining a large, safety-critical system. You use a model to predict which components are most likely to fail. Then you examine those identified components carefully and perform perfective and preventive maintenance on each one.
Give an example of problem analysis where the problem components are relatively simple, but the difficulty in solving the problem lies in the interconnections among sub-problem components in software engineering. Many software engineers think that an antiballistic-missile system would require at least 10million lines of codes; some estimates range as high as 100 million. By comparison, the software supporting the American space shuttle consists of 3million lines of codes, including computers on the ground controlling the launch and the flight; there were 100,000 lines of code in the shuttle itself. Thus, an antimissile software system would require the testing of an enormous amount of code.
Many organizational buy commercial software, thinking it is cheaper than developing and maintaining software in-house. Describe tye pros and cons of using COTS software. For example, what happen if the cots products are no longer supported by their vendors? End-of-life (EOL) is a term used with respect to a product supplied to customers, indicating that the product is in the end of its useful lifetime and a vendor will no longer be marketing, selling, or sustaining a particular product and may also be limiting or ending support for the product. In the specific case of product sales, the term end-of-sale (EOS) has also been used.
