Defining properties is optional, though they do allow to declaratively control the different properties characteristics, including the ability to associate one with a converter.

定义属性是可选的，尽管他们允许声明式的控制不同属性的特征，包括和一个转换器关联。

youdao

The optional match section of the iptables command specifies the characteristics that a packet should have to match the rule, such as source and destination address, protocol, etc.

iptables 命令的可选 match 部分指定信息包与规则匹配所应具有的特征（如源和目的地地址、协议等）。

youdao

These characteristics can be found in requirements and SOA solutions in various organizations today, although these characteristics are optional for SOA and mandatory for cloud.

这些特征可在当今很多组织的SOA解决方案及需求中找到，只不过在SOA中它们是可选的，而在云计算中它们是必需的。

youdao