Concurrent engineering is a work methodology emphasizing the parallelisation of tasks, sometimes called simultaneous engineering or integrated product development using an integrated product team approach. It refers to an approach used in product development in which functions of design engineering, manufacturing engineering, other functions are integrated to reduce the time required to bring a new product to market. A 2008 publication described concurrent engineering as a new design management system that has matured in recent years to become a well-defined systems approach to optimizing design and engineering cycles. Concurrent engineering has been implemented in a number of companies and universities, most notably in the aerospace industry. Beginning in the early 1990s, CE was adapted for use in the information and content automation field, providing a basis for organization and management of projects outside the physical product development sector for which it was designed. Organizations such as the European Space Agency's Concurrent Design Facility make use of concurrent design to perform feasibility studies for future missions.
The basic premise for concurrent engineering revolves around two concepts. The first is the idea that all elements of a product's life-cycle—from functionality, assembly, maintenance, environmental impact, disposal and recycling—should be taken into careful consideration in the early design phases; the second concept is that design activities should all be occurring at the same time, i.e. concurrently. The idea is that the concurrent nature of these activities increases productivity and product quality; this way and redesigns can be discovered early in the design process when the project is still flexible. By locating and fixing these issues early, the design team can avoid what become costly errors as the project moves to more complicated computational models and into the actual manufacturing of hardware; as mentioned above, part of the design process is to ensure that the product's entire life cycle is taken into consideration. This includes establishing user requirements, propagating early conceptual designs, running computational models, creating physical prototypes, manufacturing the product.
Included in this process is taking into full account funding, workforce capability, time requirements. A 2006 study claimed that a correct implementation of the concurrent design process can save a significant amount of money, that organizations have been moving to concurrent design for this reason, it is highly compatible with systems thinking and green engineering. Concurrent engineering replaces the more traditional sequential design flow, or "Waterfall Model". In Concurrent Engineering an iterative or integrated development method is used instead; the Waterfall method moves in a linear fashion, starting with user requirements and sequentially moving forward to design and implementation, until you have a finished product. In this design system, a design team would not look backward or forward from the step it is on to fix or anticipate problems. In the case that something does go wrong, the design must be scrapped or altered; the concurrent or iterative design process encourages prompt changes of tack, so that all aspects of the life cycle of the product are taken into account, allowing for a more evolutionary approach to design.
The difference between the two design processes can be seen graphically in Figure 1. A significant part of the concurrent design method is that the individual engineer is given much more say in the overall design process due to the collaborative nature of concurrent engineering. Giving the designer ownership is claimed to improve the productivity of the employee and quality of the product, based on the assumption that people who are given a sense of gratification and ownership over their work tend to work harder and design a more robust product, as opposed to an employee, assigned a task with little say in the general process. Concurrent design comes with a series of challenges, such as implementation of early design reviews, dependency on efficient communication between engineers and teams, software compatibility, opening up the design process; this design process requires that computer models are exchanged efficiently, something that can be difficult in practice. If such issues are not addressed properly, concurrent design may not work effectively.
It is important to note that although the nature of some project activities project imposes a degree of linearity—completion of software code, prototype development and testing, for example—organizing and managing project teams to facilitate concurrent design can still yield significant benefits that come from the improved sharing of information. Service providers exist that specialize in this field, not only training people how to perform concurrent design but providing the tools to enhance the communication between the team members. Cross-functional teams include people from different area of the workplace that are all involved in a particular process, including manufacturing and software design, so forth. Doing several things at once, such as designing various subsystems is critical to reducing design time and is at the heart of concurrent engineering. Incremental information sharing helps minimize the chance that concurrent product realization will lead to surprises. "Incremental" meaning that as soon as new information becomes available, it is shared and integrated into the design.
Cross-functional teams are important to the effective sharing of in
A concurrency in a road network is an instance of one physical roadway bearing two or more different route numbers. When two roadways share the same right-of-way, it is sometimes called commons. Other terminology for a concurrency includes overlap, duplex, multiplex, dual routing or triple routing. Concurrent numbering can become common in jurisdictions that allow it. Where multiple routes must pass between a single mountain crossing or over a bridge, or through a major city, it is economically and advantageous for them all to be accommodated on a single physical roadway. In some jurisdictions, concurrent numbering is avoided by posting only one route number on highway signs. Most concurrencies are a combination of two route numbers on the same physical roadway; this is practically advantageous as well as economically advantageous. Some countries allow for concurrencies to occur, others do not allow it to happen. In those nations which do permit concurrencies, it can become common. In these countries, there are a variety of concurrences.
An example of this is the concurrency of Interstate 70 and I-76 on the Pennsylvania Turnpike in western Pennsylvania. I-70 merges with the Pennsylvania Turnpike so the route number can continue east into Maryland. A triple Interstate concurrency is found in Wisconsin along the five-mile section of I-41, I-43, I-894 in Milwaukee, Wisconsin; the concurrency of I-41 and I-43 on this roadway is an example of a wrong-way concurrency. The longest Interstate highway concurrency is I-90 for 265 miles across Indiana and Ohio. There are examples of eight-way concurrencies: I-465 around Indianapolis and Georgia State Route 10 Loop around downtown Athens, Georgia. Portions of the 53-mile I-465 overlap with I-74, US Highway 31, US 36, US 40, US 52, US 421, State Road 37 and SR 67—a total of eight other routes. Seven of the eight other designations overlap between exits 46 and 47 to create an eight-way concurrency. In the United States, concurrencies are marked by placing signs for both routes on the same or adjacent posts.
The federal Manual on Uniform Traffic Control Devices prescribes that when mounting these adjacent signs together that the numbers will be arranged vertically or horizontally in order of precedence. The order to be used is Interstate Highways, U. S. Highways, state highways, county roads, within each class by increasing numerical value. Several states do not have any concurrencies, instead ending routes on each side of one. There are several circumstances. One example occurs along the Oklahoma–Arkansas state line. At the northern end of this border Oklahoma State Highway 20 runs concurrently with Arkansas Highway 43 and the two highways run north–south along the boundary. Concurrencies are found in Canada. British Columbia Highway 5 continues east for 12 kilometres concurrently with Highway 1 and Highway 97, through Kamloops; this stretch of road, which carries Highway 97 south and Highway 5 north on the same lanes, is the only wrong-way concurrency in British Columbia. In Ontario, the Queen Elizabeth Way and Highway 403 run concurrently between Burlington and Oakville, forming the province's only concurrency between two 400-series highways.
The concurrency was not in the original plan which intended for both the QEW and Highway 403 to run parallel to each other, as the Hamilton–Brantford and Mississauga sections of Highway 403 were planned to be linked up along the corridor now occupied by Highway 407. It was planned for the Mississauga section of Highway 403 would be renumbered as Highway 410 but this never came to pass. Highway 403 was signed concurrently along the Queen Elizabeth Way in 2002, remedying the discontinuity to avoid confusing drivers that wanted to travel between the two segments without using the toll Highway 407. Nonetheless, many surface street signs referring to that section of freeway with the QEW/Highway 403 concurrency still only use the highway's original designation of QEW, although the MTO has updated route markers on the QEW to reflect the concurrency. In the United Kingdom, routes do not run concurrently with others. Where this would occur, the roadway takes the number of only one of the routes, while the other routes are considered to have a gap and are signed in brackets.
An example is the meeting of the M60 and the M62 northwest of Manchester: the motorways coincide for the seven miles between junctions 12 and 18 but the motorway between those points is only designated as the M60. European route numbers as designated by UNECE may have concurrencies, but since the E-route numbers are unsigned and unused in the UK, the existence of these concurrencies is purely theoretical. In Sweden and Denmark, the most important highways use only the European route numbers that have cardinal directions. In Sweden the E6 and E20 run concurrently for 280 kilometres. In Denmark the E47 and E55 run concurrently for 157 kilometres. There are more shorter concurrencies. There are two stretches in Sweden
Concurrency (computer science)
In computer science, concurrency refers to the ability of different parts or units of a program, algorithm, or problem to be executed out-of-order or in partial order, without affecting the final outcome. This allows for parallel execution of the concurrent units, which can improve overall speed of the execution in multi-processor and multi-core systems. In more technical terms, concurrency refers to the decomposability property of a program, algorithm, or problem into order-independent or partially-ordered components or units. A number of mathematical models have been developed for general concurrent computation including Petri nets, process calculi, the parallel random-access machine model, the actor model and the Reo Coordination Language; as Leslie Lamport notes, "While concurrent program execution had been considered for years, the computer science of concurrency began with Edsger Dijkstra's seminal 1965 paper that introduced the mutual exclusion problem.... The ensuing decades have seen a huge growth of interest in concurrency—particularly in distributed systems.
Looking back at the origins of the field, what stands out is the fundamental role played by Edsger Dijkstra". Because computations in a concurrent system can interact with each other while being executed, the number of possible execution paths in the system can be large, the resulting outcome can be indeterminate. Concurrent use of shared resources can be a source of indeterminacy leading to issues such as deadlocks, resource starvation. Design of concurrent systems entails finding reliable techniques for coordinating their execution, data exchange, memory allocation, execution scheduling to minimize response time and maximise throughput. Concurrency theory has been an active field of research in theoretical computer science. One of the first proposals was Carl Adam Petri's seminal work on Petri nets in the early 1960s. In the years since, a wide variety of formalisms have been developed for modeling and reasoning about concurrency. A number of formalisms for modeling and understanding concurrent systems have been developed, including: The parallel random-access machine The actor model Computational bridging models such as the bulk synchronous parallel model Petri nets Process calculi Calculus of communicating systems Communicating sequential processes model π-calculus Tuple spaces, e.g. Linda Simple Concurrent Object-Oriented Programming Reo Coordination LanguageSome of these models of concurrency are intended to support reasoning and specification, while others can be used through the entire development cycle, including design, proof and simulation of concurrent systems.
Some of these are based on message passing. The proliferation of different models of concurrency has motivated some researchers to develop ways to unify these different theoretical models. For example and Sangiovanni-Vincentelli have demonstrated that a so-called "tagged-signal" model can be used to provide a common framework for defining the denotational semantics of a variety of different models of concurrency, while Nielsen and Winskel have demonstrated that category theory can be used to provide a similar unified understanding of different models; the Concurrency Representation Theorem in the actor model provides a general way to represent concurrent systems that are closed in the sense that they do not receive communications from outside. The mathematical denotation denoted by a closed system S is constructed better approximations from an initial behavior called ⊥S using a behavior approximating function progressionS to construct a denotation for S as follows: DenoteS ≡ ⊔i∈ω progressionSiIn this way, S can be mathematically characterized in terms of all its possible behaviors.
Various types of temporal logic can be used to help reason about concurrent systems. Some of these logics, such as linear temporal logic and computation tree logic, allow assertions to be made about the sequences of states that a concurrent system can pass through. Others, such as action computational tree logic, Hennessy–Milner logic, Lamport's temporal logic of actions, build their assertions from sequences of actions; the principal application of these logics is in writing specifications for concurrent systems. Concurrent programming encompasses programming languages and algorithms used to implement concurrent systems. Concurrent programming is considered to be more general than parallel programming because it can involve arbitrary and dynamic patterns of communication and interaction, whereas parallel systems have a predefined and well-structured communications pattern; the base goals of concurrent programming include correctness and robustness. Concurrent systems such as Operating systems and Database management systems are designed to operate indefinitely, including automatic recovery from failure, not terminate unexpectedly.
Some concurrent systems implement a form of transparent concurrency, in which concurrent computational entities may compete for and share a single resource, but the complexities of this competition and sharing are shielded from the programmer. Because they use shared resources, concurrent systems in general require the inclusion of some kind of arbiter somewhere in their implementation, to control access to those resources; the use of arbiters introduces the possibility of indeterminacy in concurrent computation which has major implications for practice including correctness and performance