Component-based approaches

The aim must be to invest in the development of a component library as a capital asset (see Figure 10.1). Like any investment, this one requires money to be spent for a while before any payback is seen. A conventional software development organization requires a considerable shift of attitudes and strategy to adopt a component-based approach. Like all... 

Components and component-based development are rapidly becoming buzzwords like those before them, they bring a mixture of hype and real technical promise. The main advantages of adopting a component-based approach to overall development are as follows. 

Reuse Lemmas (1) If you reuse a specification, try a component-based approach Implement against the interface and defer binding to the implementation. 

Reuse Lemmas (1) If you reuse a specification, try a component-based approach implement against the interface and defer binding to the implementation. (2) Reuse of specifications leads to reuse of implementations. In particular, whenever you can implement standardized interfaces, whether domain-specific or for infrastructure services, you enable the reuse of all other implementations that follow those standards. (3) Successful reuse needs thorough interface specifications. (4) If you can componentize your problem domain descriptions themselves and reuse domain models, you greatly enhance your position to reuse interface specifications and implementations downstream. 

Component-Based Approaches, Test Designs, and Methods.132... 

Case Study 2 A Component-Based Approach from Human ... 

In each of these disciplines several more specific goals can be identified (see text box). Because of this, a diverse set of approaches has been developed for analyzing and assessing the toxicities of chemical mixtures, which can be grouped into 3 major classes 1) mixture experiments in which the toxicity of the mixture is characterized without making any effort to connect it to the toxicities of the components 2) whole mixture approaches, that is, inferring from mixture effects the toxicity contributions of the individual components and 3) component-based approaches, that is, inferring from the mixture components their joint toxicity. 

Component-based approaches are used as prognosis instruments, to predict the effects of chemical mixtures, or to unravel interactions between mixture components. They are restricted to mixtures with a defined chemical composition. As component-based approaches allow predicting the toxicity of mixtures that are not yet found in the environment, they are the fundamental option for prospective assessments, such as the setting of environmental quality standards. 

Fundamental for both the whole mixture and component-based approaches are 2 concepts of mixture toxicity, the concepts of CA and IA or response addition (RA). CA assumes similar action of the chemicals in the mixture, while IA takes dissimilar action as the starting point. In practice, this means that CA is used as the reference when testing chemicals with the same or similar modes of action, while IA is the preferred reference in case of chemicals with different modes of action. 

Component-based approach. This is an option if the mixture composition can be determined, for example, by means of chemical analysis, and if a mixture model is available that can predict the mixture effects. The mixture model can either be simple, for example, summation of PEC/PNEC ratios over all compounds into a hazard index (HI) moderately complex, for... 

Figure 5.3 Three alternative options to assess the risk of mixtures 1) mixtures can be tested in the field or the laboratory, particularly completely unknown mixtures 2) if toxicity data on (sufficient) similar mixtures are available, the mixture can be evaluated using a reference value, for example, in a PEC/PNEC ratio and 3) mixtures of which the components are known can be evaluated using component-based approaches (mixture algorithms). PEC = Predicted Environmental Concentration, PNEC = Predicted No Effect Concentration.

This section outlines the current scientific state of the art in the assessment of human health risks for chemical mixtures. It focuses on the gathering, assessment, and evaluation of effect data. The reader is referred to Chapter 1 for detailed information on exposure assessment of chemical mixtures. The section starts with an overview of methods commonly used to obtain effect data on chemical mixtures. This is followed by an overview of the current mixture approaches in human health assessments, that is, the whole mixture approach for common mixtures and the component-based approach. The section concludes with a paragraph on uncertainties in human health assessments of chemical mixtures. 

Of the 3 mixture approaches outlined in Section 5.2 (i.e., the common whole mixture, unique whole mixture, and component-based approaches), the first and the last are widely used in the assessment of human health effects. Common whole mixture approaches are generally referred to as whole mixture approaches in human health assessments, emphasizing the fact that the toxicity data relate to the mixture as a whole, instead of its components (USEPA 1986, 2000b ATSDR 2004a). However, because the term whole mixture equally applies to the assessment of unique mixtures—which are rarely addressed in human health assessment procedures—the term common whole mixture approach is used here. 

Component-Based Methods. Component-based approaches (Figure 5.5) are generally used to evaluate human health risks from exposure to a limited number of chemicals as a mixture. Key issues for component-based assessments include similarity in dose-response curves and similar vs. independent toxic modes of action (MOAs) among mixture components. A distinction can be made between 1) assessments using relatively simple additivity methods without the consideration of potential interaction effects, and 2) assessments that include data on toxicological interactions. Both types of assessments are discussed in more detail below. 

Component-based approaches are based on the assumption that the toxicity of a mixture can be assessed based on knowledge of the individual components in combination with the application of a mixture model. A component-based approach is generally applied to mixtures with relatively few chemical components that have all or partially been identified. If only partial information is available, the approach corresponds to the partially characterized boxes in Figure 5.11. 

Distinction is made between approaches for assessment of whole mixtures and component-based approaches. The most accurate assessment results are obtained by using toxicity data on the mixture of concern. If these are not available, alternatives can be used, such as the concept of sufficient similarity, (partial) characterization of mixtures, and component-based methods. Which method is most suitable depends on the situation at hand. A single mixture assessment method that always provides accurate risk estimates is not available. 

Component-Based Approaches The design and implementation of a complex mixture toxicity testing regimen is a laborious undertaking [12]. Once... 

The development of AL values can aid the component-based approaches to risk assessment based on dose addition. AL values can be developed for the critical effect and for secondary effects. For chemicals with older AL values developed from point estimates of the POD (e.g., NOAEL values), when more recent and more thorough dose response data are available, the AL should be re-derived using more advanced (i.e., benchmark dose analysis) approaches to estimating the POD. 

Process integration offers the potential to couple different tools more flexibly and to provide high quality support for the developer at the same time. Explicit, easily modifiable method fragments guide the developer during activities across multiple tools, while the tools themselves only cover a limited scope. In this way, process integration complements data integration mechanisms, which maintain structural consistency between documents of different tools, and component-based approaches such as the CAPE-OPEN approach [72]. 

The European process industries have therefore embarked on the CAPE-OPEN initiative [71] in order to accomplish a standardization of simulation interfaces, such that a component-based approach can be followed. This standard has been defined at the conceptual level through UML models. At the middleware implementation level, the standard is both defined in DCOM [847] and CORBA [877]. In IMPROVE, the CORBA version is used. 

A Hierarchical, Component Based Approach to Screening Properties of Soft Matter... 

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