Like system properties, global property descriptions are stored in the global item class by the connector.
与系统属性相似，连接器将全局属性描述存储在一个全局条目类中。
Property descriptions are organized into item classes, which were discussed in some detail in the last article.
属性描述组织成条目类，这在前一篇文章中详细讨论过。
Because the example connector cannot know about the existence of the ad-hoc properties ahead of time, it does not store their property descriptions in the global item class.
因为示例连接器无法提前知道专用属性的存在，所以不在全局条目类中存储它们的属性描述。
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