The Nature of Classification

The greatest enemy of the truth is not the lie—deliberate, contrived, and dishonest, but the myth—persistent, pervasive and unrealistic. 

The organization of information is a necessary and critical function, but it is also an intrinsically appealing and satisfying enterprise that is required to master our environs. The world is overwhelmingly complex. At a mundane level, obtaining understanding of these complexities is an automatic, essential, and basic process that is necessary for survival. As a scientific enterprise, attempting to determine order in the universe rests at the core of all endeavors. 

The central tenet of this book is that the current diagnostic system is questionable because diagnostic entities have not received the type of empirical scrutiny that should be applied to them. Without further scrutiny there is a risk that psychiatric entities will attain mythic legitimacy, based largely on their codification within the DSM. This is not a small problem, and we would suggest that mental health researchers and practitioners be very concerned about this because we have quite possibly constructed a nosologic house of cards.  

Classification also facilitates communication. A classification system represents the development of a common language that allows for consistency in communication. Clinicians can be confident that they are talking about the same thing when they use classification labels for disorders x, y, or z- 

Instead, Cronbach and Meehl (1955) suggested that classification should be based on a construct validation approach. Construct validation involves developing a theory about a construct that is defined by a set of interconnected laws. These laws are ideas that relate constructs to one another as well as to observable behaviors. The set of constructs, laws, and observable behaviors is called a nomological network. 

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The header delivers any relevant additional information helpful to define the nature of the task and its peculiarities. The body contains the variables, which are usually floats. Next, there are the integers defining the class to which the patterns belong (indispensable for classification tasks) and pattern names. 

Drilling fluids are classified as to the nature of the continuous phase gas, water, oil, or synthetic. Within each classification are divisions based on composition or chemistry of the fluid or the dispersed phase. 

Alkyd resins are usually referred to by a brief description based on certain classification schemes. Erom the classification the general properties of the resin become immediately apparent. Classification is based on the nature of the fatty acid and oil length. 

The nature of a toxic effect and the probabiUty of its occurring are often related to the number of exposures. The classification of toxic effects, and descriptions of toxicology tests, may be dictated by the number of exposures that eUcit toxic effects. The following terms are convenient in this respect. 

Enzyme Nomenclature. The number of enzymes known exceeds two thousand. A system of classification and nomenclature is required to identify them unambiguously. During the nineteenth century, it was the practice to identify enzymes by adding the suffix -in to the name of their source. Names such as papain, ftcin, trypsin, pepsin, etc, are still in use. However, this system does not give any indication of the nature of the reaction catalyzed by the enzyme or the type of substrate involved. 

These methods of classification are not mutually exclusive. Thus filters usually are divided first into the two groups of cake and clarifying equipment, then into groups of machines using the same land of driving force, then further into batch and continuous classes. This is the scheme of classification underlying the discussion of filters of this subsection. Within it, the other aspects of operating cycle, the nature of the sohds, and additional factors (e.g., types and classification of filter media) will be treated explicitly or implicitly. 

The method used for grinding pressed cakes depends upon the nature of the cake, its purity, residual oil, and moisture content. If the whole cake is to be pulverized without removal of fibrous particles, it may be ground in a hammer mill with or without air classification. A 15-kW (20-hp) hammer mill with an air classifier, grinding pressed cake, had a capacity of 136 kg/h (300 Ib/h), 90 percent through No. 200 sieve a 15-kW (20-lm) screen-hammer mill grinding to 0.16-cm (Vi6-in) screen producea 453 kg/h (1000 Ib/h). In many cases the hammer mill is used merely as a preliminaiy disintegrator, followed by an attrition mill. Typical performance of the attrition mill is given in Table 20-25. A finer product may be obtained in a hammer mill in closed circuit with an external screen or classifier. 

Kinds of Catalyzed Organic Reactions A fundamental classification of organic reactions is possible on the basis of the lands of bonds that are formed or destroyed and the natures of eliminations, substitutions, and additions of groups. Here a more pragmatic hst of 20 commercially important lands or classes of reactions will be discussed. In all instances of sohd-catalyzed reactions, chemisorption is a primary step. Often molecules are dissociated on chemisorption into... 

A classification of processes can be made with respecl to the nature of the reaction product, as follows ... 

All the well-characterized proteinases belong to one or other of four families serine, cysteine, aspartic, or metallo proteinases. This classification is based on a functional criterion, namely, the nature of the most prominent functional group in the active site. Members of the same functional family are usually evolutionarily related, but there are exceptions to this rule. We... 

The external error mode is the observable form of the error. This can often be classified in several ways. In the current example the external error modes were "right action on wrong object" (wrong valve closed) and "action omitted" (the correct valve was not closed). The exact form of the external error mode will obviously depend on the nature of the task. A comprehensive classification of external error modes is provided in Chapter 4. 

The classification structure for PIFs used in this chapter is based on the model of human error as arising from a mismatch between demands and resources which was described in Chapter 1, Section 1.6 (Figure 1.6). In this model demands were seen as requirements for human performance which arise from the characteristics of the process environment (e.g., the need to monitor a panel or to be able to fix a seal in a flange) and the nature of the human capabilities to satisfy these demands (e.g., skills of perception, thinking, and physical action). These demands are met by the individual and group resources of personnel and the extent to which the design of the task allows these resources to be effectively deployed. Where demands exceeded resources, errors could be expected to occur. 

This analysis is applied to each operation at the particular level of the HTA being evaluated. In most cases the analysis is performed at the level of a step, for example. Open valve 27B. For each operation, the analyst considers the likelihood that one or more of the error types set out in classification in Figure 5.7 could occur. This decision is made on the basis of the information supplied by the PIF analysis, and the analyst s knowledge concerning the types of error likely to arise given the nature of the mental and physical demands of the task and the particular configuration of PIFs that exist in the situation. The different error categories are described in more detail below ... 

Two-phase suspension systems produce beaded products with broader particle-size distribution (e.g., 1-50 /rm). The microspherical particles usually need to be classified repeatedly to reduce the particle-size distribution in order to improve the resolution and efficiency in the separation for use in chromatography. The actual classification process depends on the size range involved, the nature of the beaded product, and its intended applications. Relatively large (>50 /rm) and mechanically stable particles can be sieved easily in the dry state, whereas small particles are processed more conveniently in the wet state. For very fine particles (<20 /rm), classification is accomplished by wet sedimentation, countflow setting, countflow centrifugation, or air classification. 

The classification given in Table 1.2 is based on the various forms that corrosion may take, but the terminology used in describing corrosion phenomena frequently places emphasis on the environment or cause of attack rather than the form of attack. Thus the broad classification of corrosion reactions into wet or dry is now generally accepted, and the nature of the process is frequently made more specific by the use of an adjective that indicates type or environment, e.g. concentration—cell corrosion, crevice corrosion, bimetallic corrosion and atmospheric corrosion. 

The Natural Durability Classification of Timber. 1981. Tech. Note 40. BRE. 

The old classification of bodies into solids, liquids, and gases, based on differences in viscosity and elasticity, is not altogether satisfactory. We shall therefore adopt a method in which bodies are divided into two classes according to the nature of their... 

Another classification system, first suggested by Carothers in 1929, is based on the nature of the chemical reactions employed in the polymerisation. Here the two major groups are the condensation and the addition polymers. Condensation polymers are those prepared from monomers where reaction is accompanied by the loss of a small molecule, usually of water, for example polyesters which are formed by the condensation shown in Reaction 1.1. 

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