Database tier

Database Tier. In a three-tier programming architecture, the database tier resides on a server computer with access to the databases and the programs that manage them. 

Chemical inventory system for Tier I/II information. Includes capacity to inventory quantity and location information. Contains database of 3100 hazardous chemicals. 

Primarily recordkeeping system for individual facilities. Includes information on chemicals and manufacturers and records of accidents and training. Chris Plus adds capability of storing and printing MSDS information and assists with the preparation of Tier I and Tier II reports and right-to-know requests. Doth systems contain database of 600 toxic substances and synonyms. 

In our view, architecture is not only about Gothic-scale structures but is also about all structures and relationships used down to the level of code.1 The decision to use a four-tier structure, with a thin client, a Web server, a business application server, and a database, is architectural. But, in the extreme, we consider a consistent use of getXQ and setX(x) methods also to be part of the (detailed) architecture. This view leads to a somewhat less formal definition of architecture. 

Cumulative distributions of the logarithms of NOELs were plotted separately for each of the stmcmral classes. The 5th percentile NOEL was estimated for each stmctural class and this was in mrn converted to a human exposure threshold by applying the conventional default safety factor of 100 (Section 5.2.1). The stmcmre-based, tiered TTC values established were 1800 p,g/person/ day (Class I), 540 pg/person/day (Class II), and 90 pg/person/day (Class III). Endpoints covered include systemic toxicity except mutagenicity and carcinogenicity. Later work increased the number of chemicals in the database from 613 to 900 without altering the cumulative distributions of NOELs (Barlow 2005). 

The data development effort planned by the EPA has the potential to add significantly to the database on endocrine disruption. The use of standardized laboratory protocols and careful evaluation procedures will maximize the value of the results. In addition to providing data relevant to the regulation of the chemicals being tested, the data will also be useful for understanding the relationship between the relatively simple endpoints examined in some of the Tier I screens (such as receptor binding) and the development of more toxicologically relevant apical endpoints noted in the Tier II tests. 

A three-tiered architecture includes one more node between the client and the database server—the middle tier. In a three-tiered architecture, business logic is offloaded from the client and the database server nodes to the middle tier. In fact, you can choose to further distribute the business logic among more than one middle tier node and still call it a three-tiered (or K-tiered) architecture because the idea is similar. Note that the tiers do not have to be physically separated. You can have both the middle tier server and the database server collocated on the same physical computer but running in different processes with separate memory spaces. Modem hardware architecture can partition a single hardware box into multiple virtually separate computers or domains. Typically, a three-tiered architecture supports a Web-based thin client although it can also work with a rich client. 

Expensive system resources can be more effectively managed. For example, the middle tier can create a pool of database connections that is shared by all clients. It can also implement a complex data caching capability to boost performance. 

Tier 2 PRA process involved developing environmental exposure data and chronic toxicity data distributions for individual POPs. The mean concentrations of POPs in local marine water measured at various locations were used as exposure data in the construction of the exposure distribution. The chronic toxicity data distribution was established based on published international acute toxicity data (LC50, EC50) on a variety of aquatic organisms tested in many jurisdictions, drawn primarily from the USEPA ECOTOX database (2002) (available at http //www.epa.gov/ ecotox). If the upper 5th centile of the measured chemical exposure data distribution did not exceed the lower 5th centile of its estimated chronic toxicity distribution, the potential ecological risk posed by the chemical was judged to be tolerable (Hall and Giddings, 2000). 

Wauchope, R.D., Hornsby, A G., Goss, D.W., Burt, J.P. (1991) The SCS/ARS/SCS Pesticides Properties Database A set of parameter values for first-tier comparative water pollution risk analysis. Proceedings, National Pesticide Conference, Brookfield, Virginia, November 8-9, 1990, pp. 455 -70. 

Current efforts to extrapolate mixture effects are dominated by TU-based approaches, which result in prediction error when the models are used for situations where the concentrations deviate from the original effect level that is used to define TU. Provided that the data are available, mixture extrapolation at the species level may improve by using the proposed higher tier protocols. It should be acknowledged, however, that the data needed for such an enterprise at the species level are not systematically stored in databases, as is the case for the databases available to construct SSDs (see Section 5.6.1). For a significant advancement, researchers therefore should strive for full-curve modeling over point-estimate models (i.e., to model at Tier-2 and Tier-3). The major requirement would therefore be to not only produce but also report systematically on concentration response functions for individual compounds, as this would allow prediction of any yet untested mixture for the same biological response. 

The web clients are often called thin clients in the enterprise application, because they do not directly query databases, execute complex business logic, or connect to legacy applications. Such heavyweight operations are off-loaded to the components in the web tier or business tier underneath in order to utilize the security, speed, service, and reliability provided by J2EE server-side technologies. The thin-client design makes the enterprise application scalable, and the development process simple and flexible. 

In order to improve performance, business logic, such as processing user and job information, is removed from the web tier and handled by the business tier. In the business tier, EJB components receive information from the web-tier components, process the format, and send the information to the database in the resource tier for storage. EJBs also retrieve data from the database in the resource tier, process them if necessary, and send them back to the web tier for display. 

COMPARISON OF DATABASES/MODELS AND THEIR USE IN RIS K AS S ES SMENT WITH A TIERED APPROACH 194 Comparison of Databases/Models 194 Case Studies A Limited Comparison 196 A Tiered Approach for Risk Assessment 198 GENERIC USE OF BIOLOGICAL MONITORING DATA 199 CONCLUSIONS AND RECOMMENDATIONS 200... 

COMPARISON OF DATABASES/MODELS AND THEIR USE IN RISK ASSESSMENT WITH A TIERED APPROACH... 

Risk notification accompanied by generic reasonable worst-case exposure with a default value of dermal absorption rate, which is a specific percentage penetration value via the dermal route. This screening tier should be quite simple, checking for the kinds of users and product use. Exposure estimates are retrieved from high-end indicative values (from databases or models) or from reasoned cases. Models suited to aid the process are EUSES/USES, SCIES/MCCEM, THERdbASE and the simple models in CONSEXPO and InPest with reasonable worst-values . 

Tiered approaches to dermal exposure and risk assessment have been developed (OECD, 1997 de Heer et al, 1999 Harney, 2000 EC, 2002). Although the number of tiers differ depending on the specific approach, common to all approaches is the sequential refinement of the value used for dermal absorption in the risk assessment. For example, in a Tier 1 risk assessment, a conservative value of 100 % dermal absorption is often used. If required, a more refined default may be justifiable, based on a number of considerations such as the physico-chemical properties of the substance and the toxicological database. Use of dermal absorption data would be the third tier. Biological monitoring data would be a potential fourth tier, if required. 

If the results of a preliminary risk assessment, using a Tier 1 approach, do not generate acceptable risk levels, an examination of the physico-chemical properties of the substance, as well as the toxicological database of the product, may yield a justification for a lower dermal absorption default. A weight-of-evidence approach should be used, e.g. both the physico-chemical information and the toxicological database should support the reduced default. 

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