现实世界的实体间往往存在着复杂的语义关系,而且实体间的关系往往是相互的。现有数据库无论是扩展了对象关系模型的Oracle,还是首次提出逆向关系定义的ODMG(object data management group),它们对现实世界中实体之间复杂语义关系及其...现实世界的实体间往往存在着复杂的语义关系,而且实体间的关系往往是相互的。现有数据库无论是扩展了对象关系模型的Oracle,还是首次提出逆向关系定义的ODMG(object data management group),它们对现实世界中实体之间复杂语义关系及其逆向关系的描述和处理依然存在着很大的不足。为了更好地表述和处理现实世界中实体间复杂的语义关系,提出了一种能够简易描述实体间复杂语义的新方法。介绍了该方法如何针对复杂语义关系建立模型和插入对象,指出了该方法相对于传统模型的优越性,设计实现了实体间逆向关系和目标对象类的自动创建和生成机制,分析了数据库一致性维护问题。比较了基于新方法实现的DBMS(data base management system)和Oracle的性能,指出了基于新方法的DBMS存在的问题。展开更多
Most manufacturers of solar modules guarantee the minimum performance of their modules for 20 to 25 years, and 30-year warranties have been introduced. The warranty typically guarantees that the modules will perform t...Most manufacturers of solar modules guarantee the minimum performance of their modules for 20 to 25 years, and 30-year warranties have been introduced. The warranty typically guarantees that the modules will perform to at least 90% capacity in the first 10 years and to at least 80% in the following 10 - 15 years. Early degradation resulting from design flaws, materials or processing issues is often apparent from startup to the first few years in service. Importantly, many module failures and performance losses are the result of gradual accumulated damage resulting from long-term outdoor exposure in harsh environments, referred. Many of these processes occur on relatively long time scales and the various degradation processes may be chemical, electrical, thermal or mechanical in nature. These are either initiated or accelerated by the combined stresses of the service environment, in particular solar radiation, temperature and moisture, and other stresses such as salt air, wind and snow. Accelerated Life Testing (ALT) test methodology is normally predicated on first being able to reproduce a specific degradation or failure mode without altering it (correlation);and, second, to produce that result in less than real-time acceleration. Degradation and failure may result when an applied stress exceeds material or product strength. This may be a one-time catastrophic event, the result of cyclic fatigue, or a gradual decline in requisite properties due to ageing mechanisms. Engineers in the manufacturing industries have used accelerated test (AT) experiments for many decades. The purpose of AT experiments is to acquire reliability information quickly. Test units of a material, component, subsystem or entire systems are subjected to higher-than-usual levels of one or more accelerating variables such as temperature or stress. Then the AT results are used to predict life of the units at use conditions. The extrapolation is typically justified (correctly or incorrectly) on the basis of physically motivated models or a combin展开更多
文摘现实世界的实体间往往存在着复杂的语义关系,而且实体间的关系往往是相互的。现有数据库无论是扩展了对象关系模型的Oracle,还是首次提出逆向关系定义的ODMG(object data management group),它们对现实世界中实体之间复杂语义关系及其逆向关系的描述和处理依然存在着很大的不足。为了更好地表述和处理现实世界中实体间复杂的语义关系,提出了一种能够简易描述实体间复杂语义的新方法。介绍了该方法如何针对复杂语义关系建立模型和插入对象,指出了该方法相对于传统模型的优越性,设计实现了实体间逆向关系和目标对象类的自动创建和生成机制,分析了数据库一致性维护问题。比较了基于新方法实现的DBMS(data base management system)和Oracle的性能,指出了基于新方法的DBMS存在的问题。
基金supported by grants from the National Natural Science Foundation of China (No. 81570728)the Natural Science Foundation of Hebei Province,China (No. H2018206358)。
文摘Most manufacturers of solar modules guarantee the minimum performance of their modules for 20 to 25 years, and 30-year warranties have been introduced. The warranty typically guarantees that the modules will perform to at least 90% capacity in the first 10 years and to at least 80% in the following 10 - 15 years. Early degradation resulting from design flaws, materials or processing issues is often apparent from startup to the first few years in service. Importantly, many module failures and performance losses are the result of gradual accumulated damage resulting from long-term outdoor exposure in harsh environments, referred. Many of these processes occur on relatively long time scales and the various degradation processes may be chemical, electrical, thermal or mechanical in nature. These are either initiated or accelerated by the combined stresses of the service environment, in particular solar radiation, temperature and moisture, and other stresses such as salt air, wind and snow. Accelerated Life Testing (ALT) test methodology is normally predicated on first being able to reproduce a specific degradation or failure mode without altering it (correlation);and, second, to produce that result in less than real-time acceleration. Degradation and failure may result when an applied stress exceeds material or product strength. This may be a one-time catastrophic event, the result of cyclic fatigue, or a gradual decline in requisite properties due to ageing mechanisms. Engineers in the manufacturing industries have used accelerated test (AT) experiments for many decades. The purpose of AT experiments is to acquire reliability information quickly. Test units of a material, component, subsystem or entire systems are subjected to higher-than-usual levels of one or more accelerating variables such as temperature or stress. Then the AT results are used to predict life of the units at use conditions. The extrapolation is typically justified (correctly or incorrectly) on the basis of physically motivated models or a combin
