An ultra-large-scale systems (ULSS) is one which has the characteristics of:
- operationally independent sub-systems;
- managerially independent components and sub-systems;
- evolutionary development;
- emergent behavior; and
- geographic distribution.
In addition to these attributes, a Northrop report argues that a ULSS:
- features decentralized data, development, evolution and operational control;
- addresses inherently conflicting, unknowable, and diverse requirements;
- evolves continuously while operating, with different capabilities being deployed and removed as warranted;
- contains heterogeneous, inconsistent and changing elements; and
- treats failure as the norm, rather than the exception, with it being extremely unlikely that all components are functioning at any one time.
Examples of ultra-large-scale systems include: the US healthcare system, US energy smart grids and global financial markets.
A system is said to be real-time if the total correctness of an operation depends not only upon its logical correctness, but also upon the time in which it is performed. Real-time systems, as well as their deadlines, are classified by the consequence of missing a deadline:
- Hard: Missing a deadline is a total system failure.
- Firm: Infrequent deadline misses are tolerable but may degrade the system’s quality of service.
- Soft: The usefulness of a result degrades after its deadline, thereby degrading the system’s quality of service.
Soft real-time systems are typically used where there is some issue of concurrent access and a need to keep a number of connected systems up to date with changing situations. A good example of this is software that maintains and updates the flight plans of commercial airliners. Such plans must be kept reasonably current, but can operate with a latency of seconds.
Massively multiplayer online game
A massively multiplayer online game (also called MMO or MMOG) is a multiplayer video game which is capable of supporting hundreds or thousands of players concurrently.
High volume and high capacity
The primary goal of volume and capacity testing is to ensure that IT capacity meets current and future business requirements in a cost-effective manner.
High availability system
High availability is a system design approach and associated service implementation that ensures a prearranged level of operational performance will be met during a contractual measurement period.
Unavailability is most often called “downtime” and its avoidance requires redundancy, fail-over, or load balancing.
People commonly refer to 24/7, but a high availability system is characterized by its specified availability level. A typical spec, what’s popularly known as “four nines availability”, is 99.99% uptime, allowing for 52.56 minutes of downtime per year. Systems such as these are used worldwide in the most important applications such as medical informatics, nuclear power, financial institutions, aeronautics, airlines, news reporting, e-commerce, online transaction processing and persistent online games.
Life-critical system or Safety-critical system
A life-critical system or safety-critical system is a system whose failure or malfunction may result in one or more of the following:
- death or serious injury to people
- loss or severe damage to equipment
- environmental harm
Risks of this sort are usually managed with the methods and tools of safety engineering. A life-critical system is designed to lose less than one life per billion (109) hours of operation. Typical design methods include probabilistic risk assessment, a method that combines failure mode and effects analysis (FMEA) with fault tree analysis. Safety-critical systems are increasingly computer-based.
The act of introducing something new, such as a new method or device.
To state, tell about, or make known in advance, especially on the basis of special knowledge.
Innovation and predictability are often seen at odds since innovation and change will reduce predictability and increase risk. The amount of added risk will increase significantly due to their size, complexity and emergent nature.
Sources: Webster’s Dictionary, Wikipedia