Glossary Flashcards
(33 cards)
Acceptance
Precisely defined condition that a system must meet in order to be accepted; a component of a requirement
Affordance
A requirement that affords an option or freedom to a user, whether or not the user chooses to exploit it
Capability
In a system specification, a function that a system is capable of but performs only when requested to by a user or another system. Functions not exposed to agents outside the system are not capabilities. However, the term is often used loosely to mean no more than “system function”. In user requirements, a capability means something a user wants to be able to do, so in this sense it is a synonym for affordance.
Constraint
A statement of restriction, modifying a requirement or set of requirements by limiting the range of acceptable solutions. Sometimes used to indicate physical limitations such as size, shape, weight. Constraints may be imposed either by users (in user requirements) or by developers with specialist knowledge, such as of safety standards (in system requirements)
Design constraint
Constraint describing an existing interface, presumably part of the design of some existing legacy system that must be complied with
Exception (event)
It may be caused by something inside or outside the system. Exception events need to be handled by appropriate exception scenarios
Exception Scenario
The desired response (Sequence of actions) to an exception event. It results in an end-state which is safe, and which is, if possible, back at some step in a normal scenario, so that users can continue with their work. In other words the goal for an exception scenario is to handle the exception event safely
Functional Requirement
Something that a system or subsystem does, presumably because a requirement made it necessary
Goal
A desired result, often at a high and abstract level. Goals are useful as the names of scenarios or use cases used to structure requirements
Inquiry cycle
A structured sequence of activities, designed to be repeated as necessary, often in a workshop, to achieve consensus among a group of stakeholders on a set of requirements
Non-functional requirement
Constraint; any requirement other than a function
Requirement
1.) A user requirement
2.) A system requirement
Scenario
A time-ordered sequence of events used to structure a set of requirements according to their actual or predicted pattern of usage
Specification
The precise definition of the required behavior and qualities of a system in a form suitable for inclusion in a contract
System requirement
Either an affordance or a constraint, forming a structured element of a system specification
User requirement
A structured statement of user or other stakeholder need (in the world), written as either an affordance or as a constraint, imposed by a user. Compare: system requirement
Validation
Checking that the requirements as documented are indeed the right ones, namely the ones that the stake-holders actually want
Verification
Demonstrating that:
1) a system meets its system specification;
2) a system in use meets its user requirements.
Verification is most often by test but can also be by inspection, analysis, or simulation
Fault Tree Analysis uses
Fault tree analysis can be used to:
understand the logic leading to the top event / undesired state.
show compliance with the (input) system safety / reliability requirements.
prioritize the contributors leading to the top event- creating the critical equipment/parts/events lists for different importance measures
monitor and control the safety performance of the complex system (e.g., is a particular aircraft safe to fly when fuel valve x malfunctions? For how long is it allowed to fly with the valve malfunction?).
minimize and optimize resources.
assist in designing a system. The FTA can be used as a design tool that helps to create (output / lower level) requirements.
function as a diagnostic tool to identify and correct causes of the top event. It can help with the creation of diagnostic manuals / processes.
Where is the most likely place for an exception to occur?
Any place that can be effected by users, other systems, state transitions
Good questions to discover exceptions
Can anything prevent you from reaching this goal?
Can anything go wrong here?
What else could when you’re in the state?
Requirements vs Constraints
Functional vs Non-Functional
Requirements – Capture Features and Functions of a system or component. Constraints – Define the Non-Functional aspects of a system or component, such as restrictions on technology, resources or techniques to be used.
Goal Headings
Goal
>Sub Goal
»Primary Scenario
»Exceptions
»Trigger
Examples of Non-Functional Requirements
Cost
Reliability
Safety
Usability
Environment
