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Verification at Each SDLC Phase

The concept of verification is an important part of the overall system validation. Lewis [1] defines verification as follows:

Verification is an iterative process aimed at determining whether the product of each step in the SDLC fulfills all the requirements levied on it by the previous step and is internally complete, consistent, and correct enough to support the next phase.

Whereas validation can be thought of as testing the final system against its original requirements, verification looks at the intermediate work product from each SDLC phase. Verification is like in-process inspection in manufacturing, where small errors introduced in the process are corrected before the product moves farther in the process.

Verification is best performed in a team approach. To verify a given phase of the SDLC, a review team should be formed, with representatives from the current phase (the phase being verified), the prior phase (that provided the input specification), and the next phase (that will rely on the output from the current phase). This puts verification responsibility on the in­dividuals that have the greatest vested interest the correctness of the current phase. In software de­velopment, this is sometimes called "n-plus-and-minus-one verification" [2].

All the verification methods to be used in the development of a system should be documented as part of a comprehensive test plan. As system
requirements and design features are defined, a corresponding test plan is developed to ensure that these requirements and features are satisfied. The test plan is started early in the project and is fleshed out in more detail as the project proceeds through each phase, as il­lustrated in Figure 1 and Figure 2.

General Verification Methods

There are several general verification methods that can be used at any point of the SDLC. Although simple in concept, these methods are valuable, especially in the require­ments, design, and program coding phases. Industry studies have shown that problems uncovered early in the SDLC are much less costly to correct than if they were allowed to go undetected until system testing, or worse, until live operation [2]. These general verification methods should be formally employed with the results documented and archived along with the rest of the system validation records.

1. By means of inspection [3], a person other than the author reviews the requirements documentation, sys­tem design, or program code in a step-by-step effort to find missing requirements, internal contradictions, evidence of weak analysis, errors, violation of stan­dards, or other problems. Pre-defined check lists are often used.

2. During walk-throughs [2,3], the designer or program­mer leads other members of the review team through the design document or program code, allowing them to question techniques, style, possible errors, violation of standards, or other problems. Walk-throughs are effective in detecting misunderstandings of system requirements or design specifications before signifi­cant effort is invested in development.

3. By means of desk checking and peer review [3] a member of the review team mentally simulates pro­gram execution in an attempt to detect errors in logic, syntax, or programming conventions. A significant number of program logic errors can be detected though desk checking that are never discovered through ac­tual program test execution.

Written Test Protocols, Test Scripts, and Test Cases

The test plan for the Integrated System Test and Accep­tance Test phases consists of a series of test protocols. Test protocols define what is being tested, why it is being tested, and how the test is to be carried out. The test protocol should also include a detailed description of the test data, test conditions, and any special equipment required. It should include a description of the expected results and how the tester should analyze the results to determine whether the test was passed. Unless the test protocol is quite simple, it must be supplemented by detailed test scripts and test cases. Test scripts provide step by step instructions to carry out the test. Test cases provide the exact test data required. The best written test plans usually employ a set of standard forms or standard formats for defining test protocols, test scripts, and test cases. A numbering system is often employed to facilitate tracing back to design elements and original requirements.

The formal definition of test protocols contrasts sharply with the ad-hoc testing method employed by many MIS departments and system users. Rather than formally plan and define test protocols, they simply sign on arid "test
drive" the system. This "on the fly" approach almost always leads to inadequate testing and higher overall system maintenance costs. With the informal approach, system errors are frequently discovered only after the system is in the use. In some cases, errors may not be discovered for years. For systems entrusted with regulatory data, this can be a time bomb.

To Be Continued


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