串的转换先计算所包括的表达式表的值，然后按照其结果类型所特定的规则转换其结果对象为字符串。
A string conversion evaluates the contained expression list and converts the resulting object into a string according to rules specific to its type.
ASQL是基于对象代数的查询语言，本文讨论了对象代数表达式的等价变换规则，利用这些规则进行查询优化。
ASQL is a query language based on object algebra. Also we discuss the rules of equivalence transform and can use these rules to process query optimization.
将组成系统的对象分解为多层，用逻辑规则表达式来描述系统对象之间的逻辑控制关系，用消息来传递控制关系。
The objects of the system are divided into several layers, and the logic control relations among different objects of the system are described with logic rule expressions and transferred by messages.
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