Figure 4 depicts the main ObjectTypes of the base device model and their relationship. The drawing is not intended to be complete. For the sake of simplicity only a few components and relations were captured to give a rough idea of the overall structure.
Figure 4 – Device model overview
The boxes in this drawing show the ObjectTypes used in this specification as well as some elements from other specifications that help understand some modelling decisions. The upper grey box shows the OPC UA core ObjectTypes from which the TopologyElementType is derived. The grey box in the second level shows the main ObjectTypes that the device model introduces. The components of those ObjectTypes are illustrated only in an abstract way in this overall picture.
The grey box in the third level shows real-world examples as they will be used in products and plants. In general, such subtypes are defined by other organizations.
The TopologyElementType is the base ObjectType for elements in a device topology. Its most essential aspect is the functional grouping concept.
The ComponentType ObjectType provides a generic definition for a Device or parts of a Device where parts include mechanics and/or software. DeviceType is commonly used to represent field Devices.
Modular Devices are introduced to support subdevices and Block Devices to support Blocks. Blocks are typically used by field communication foundations as means to organise the functionality within a Device. Specific types of Blocks will therefore be specified by these foundations.
The ConfigurableObjectType is used as a general means to create modular topology units. If needed an instance of this type will be added to the head object of the modular unit. Modular Devices, for example, will use this ObjectType to organise their modules. Block-oriented Devices use it to expose and organise their Blocks.