统一架构 第8部分：数据访问

[中文适用范围]： IEC 62541-8:2025规定了与数据访问（DA）相关的信息模型。它特别包括用于数据访问的附加VariableTypes以及NodeClasses和Attributes的补充描述，附加的Properties以及其他信息和行为。完整地址空间模型，包括所有NodeClasses和Attributes，在IEC 62541-3中进行了规定。用于检测和访问数据的服务在IEC 62541-4中进行了规定。附录A规定了如何将从OPC COM数据访问（DA）服务器接收到的信息映射到数据访问模型。本第四版取消并替代了2020年发布的第三版。本版构成技术修订。与前一版相比，本版包括以下重大技术变更：a) 增加了一个“量模型”，该模型可以从EngineeringUnit Properties中引用。该模型定义了量及其分配的单位。此外，它还提供了替代单位及其转换规则。b) 增加了ValuePrecision Property的规则：- 也可用于其他子类型，如Duration和Decimal。- 当ValuePrecision具有负值时，增加了相关规则。 [外文原描述]： IEC 62541-8:2025 defines the information model associated with Data Access (DA). It particularly includes additional VariableTypes and complementary descriptions of the NodeClasses and Attributes needed for Data Access, additional Properties, and other information and behaviour. The complete address space model, including all NodeClasses and Attributes is specified in IEC 62541‑3. The services to detect and access data are specified in IEC 62541‑4. Annex A specifies how the information received from OPC COM Data Access (DA) Servers is mapped to the Data Access model. This fourth edition cancels and replaces the third edition published in 2020. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) addition of a "Quantity Model" which can be referenced from EngineeringUnit Properties. The model defines quantities and assigned units. In addition it provides alternative units and the conversion to them. b) addition of rules for ValuePrecision Property: - can also be used for other subtypes like Duration and Decimal. - rules have been added when ValuePrecision has negative values.