Abstraction level

The next abstraction level of reaction retrieval is a so-called reaction substructure search in which both query structures arc considered as substructures. In the case of a reaction substructure search, no hydrogen atoms arc added internally during the execution of the search. Atoms which have their valencies not completely saturated are considered as open sites, where any hind ofelement could be bonded. 

The purpose of defining these classes of constraints and variables is that this will enable us to conveniently express general notions of equivalence and dominance, without explicit reference to the flowshop domain, but at a more abstract level. 

We can show separately how these objects and actions are part of what we ve already seen. Some objects and actions, such as those associated with the system management tasks, may not be relevant to what we ve seen at the abstract level (see Figure 1.18). 

An operation is a procedure, function, or subroutine. The traditional OO term is method, but we prefer to avoid confusion with the method you follow (hopefully) to develop a program. In analysis, and at a more abstract level of design, we talk about actions an action occurrence may be one or more operation invocations. 

Sequence diagrams illustrate sample occurrences of actions, but an action type can be drawn with the types of its participants and a postcondition written in terms of the participants attributes (again, whether the types represent software or domain objects), as shown in Figure 6.7. The ability to define the effects even at an abstract level is what makes it worth doing. Abstraction without precision is often just waffle until some precision is used, it is typically not reliable. 

Action refinement is about taking a large interaction with many parameters and breaking it into several steps with fewer and simpler parameters. For example, get cash(ATM, person, account, )breaks down to several steps, such as insert card(ATM pard) and enter amount(, )each of which identifies only a few parameters at a time. After the first step, the ATM system must remember whose card has been inserted so that when the later step happens, it knows which account to debit (see Figure 6.27). The association of Account x currently using ATM y is not needed at the more abstract level. Ultimately, the process can be taken down to individual keystrokes and mouse clicks. 

Let us revisit the example in Section 4.2.2, Preview Documenting a Refinement, on restocking of a vending machine (see Figure 8.4). Suppose that the warehouse inlet door for a product can jam when closed. If this outcome is an interesting exception at the abstract level, it could have been specified as such on the joint action. In the refinement, the appropriate sequence can be mapped to this abstract exception action. 

The spiral model works well in any context in which the current plan must depend on the outcome of earlier work expenditure increases along the spiral each cycle includes a review of results and risks, and it drives a refinement of the goals and plans of the next cycle. An early spiral typically covers a much broader area in requirements and a much narrower piece of design the situation reverses in later cycles. Lessons learned from any spiral feed back into the most abstract level of models that are affected. There are... 

Section 14.3 shows how some of these patterns have been applied to the case study of a video rental business at an abstract level. Section 14.4 details this model using action refinement, showing the finer-grained actions involved in the business. 

In general, the different parties that interact with an object each have a separate view of its concerns. A context model should cover all external roles and interactions, at least at an abstract level, even if split across multiple collaborations. 

In some cases, we may immediately decide that some information is not required — for example Librarian in the reserve operation. This doesn t stop you putting that information back in a later refinement —the refinement rules allow you to add parameters, but not to take them away so by paring down the parameter list at the most abstract level, you are keeping your options open. 

In identifying the system context and use cases, we have actually considered some details of user-interfaces and fine-grained interactions yet the system context seems to step back to a more abstract level of use case. This process can be rationalized as follows ... 

Grossmann (1992 65) adapts the Bauer model with the explicit aim of forming a theory of crisis from the essence of capitalist production . Following Marx s employment of the reproduction schemes, prices are assumed to be identical to values, so that deviations of demand from supply are not considered in Grossmann s abstract theory of crisis. Similarly, problems associated with credit, that in practice are always present in economic crises, are not considered relevant at this abstract level of analysis. 

This needs to be done at two levels firstly, at the level of the particular events that occurred and secondly, at a more abstract level, describing events and processes in terms of more general concepts or categories than those you used to describe the particular. In moving to this more general or abstract level, you can draw on concepts and explanatory... 

Most of the time, companies that misrepresent job openings do so unintentionally. When discussing a job opportunity with a potential employer, you can t stay on the abstract level. Early on, ask what the specific responsibilities of the job are. If the interviewer uses descriptive phrases like, "work in a low-stress environment" or "flexible work hours," ask the interviewer to define exactly what that means. Often, how an employer defines terms in its job descriptions is different from how the applicant defines them. This leads to misunderstandings. 

Design by Interface helps to remove the second obstacle by hiding the complexity of the component with simple and intuitive interfaces. Design by Interface helps to remove the third obstacle by keeping the dependencies at the abstraction level. 

Ij - abstract level, I2 - concrete level F - operator, R and A refinement modules)... 

In thinking about how to calculate the internal representation of a signal one could dream of a method where all the transformation characteristics of the individual elements of the human auditory system would be measured and modelled. In this exact approach one would have the, next to impossible, task of modelling the ear, the transduction mechanism and the neural processing at a number of different abstraction levels. 

One can doubt whether it is necessary to have an exact model of the lower abstraction levels of the auditory system (outer-, middle-, inner ear, transduction). Because audio quality judgements are, in the end, a cognitive process a crude approximation of the internal representation followed by a crude cognitive interpretation may be more appropriate then having an exact internal representation without cognitive interpretation of the differences. 

Support of different abstraction levels. The composition language should highlight the different components and their interplay at different levels of abstraction. This is important to i) facilitate specification analysis and design ii) facilitate cooperative administration and agreement on global policies Hi) support incremental specification by refinement. 

The merger is between Special Theory of Relativity and abstract quantum states through rigged Hilbert spaces the inertial frame is used to set up an abstract configuration space in laboratory space. At the abstract level, both formalisms are required. 

This approach for the development of multiple-pulse sequences is only practical if a large number of sequences can be assessed in a short period of time. The final assessment of the quality of a multiple-pulse sequence must always be based on experiments. However, for the optimization of multiple-pulse sequences, experimental approaches are, in general, too slow and too expensive (instrument time ). An attractive alternative to experiments at the spectrometer is formed by numerical simulations, that is, experiments in the computer. In simulations it is also possible to take relaxation and experimental imperfections such as phase errors or rf inhomogeneity into account. In addition to the direct translation of a laboratory experiment into a computer experiment, it is possible to numerically assess the properties of a multiple-pulse sequence on several abstract levels, for example, based on the created effective Hamiltonian. If simple necessary conditions can be defined for a multiple-pulse sequence with the... 

Fig. I. Three abstraction levels for the representation of a processing scheme.

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