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Mistakes made when following a design (or specification or requirement) or additional behaviour added to a design, i.e. corrupt behaviour, additional behaviour, omitted behaviour.
A program that controls the execution of application software and acts as an interface to the underlying hardware platform.
The behaviour of the system in the event of, and in particular its tolerance to, inputs occurring at a greater rate than expected during normal operation of the system.
Any software that is not written specifically for a given application but is obtained from other sources and is used either in source code or in object code form. Typical examples of pre-existing software include operating systems and database management systems. Commercial-off-the-shelf (COTS) software is by definition pre-existing, although other sources of pre-existing software exist, for example 'free' software published by various organisations.
Convincing evidence. (Note: This does not mean mathematically proven. Where Formal proof is required it is stated in the text.)
The probability that the software will perform to a specified requirement for a specified period of time under specified conditions.
A documentary justification of a claim.
The amount of resources within the computer system that can be used by the application software. Resources may include main memory of various categories (such as static data, stack and heap), disc space and communications bandwidth, and may include internal software resources, such as the number of files which may be simultaneously open.
Rigorous Argument A logically correct argument that is assumed to mathematically provable, but has not been proven. be
Rigorous Inspection A careful examination of a design or program component to ensure that it meets its requirements, is internally consistent and well formed, and conforms to all necessary standards and procedures. The 'Fagan' technique is one well-known inspection technique that is noted for its rigour.
Robustness The behaviour of the software in the event of spurious (unexpected) inputs, hardware faults and power supply interruptions, either in the computer system itself or in connected devices.
Safety Integrity (SI) The probability of a safety-related system satisfactorily performing the required safety functions under all the stated conditions within a stated period of time.
Safety Lifecycle The necessary activities involved in the implementation of safety-related systems, occurring during a period of time which starts at the concept phase of a project and finishes when none of the safety-related systems are any longer available for use.
Software Software comprises the programs that execute in stored program digital computers (including Programmable Logic Controllers). Software also includes any data contained within the programs or held on external storage media, which is necessary for the safe operation of the system. Software may: be developed for a particular application; be re-used from previous applications, with or without modification; have been obtained from third party software suppliers (commonly called Commercial Off The Shelf (COTS) software), e.g. database systems and operating systems or be any combination of these three types of software.
CAP 670 Air Traffic Services Safety Requirements
Software Architectural Unit A software architectural unit is defined as a set of elements protected against interference by a barricade, as illustrated below.
