A Descriptor is based on the AML Container format and the Open Packaging Conventions standard. It has the file name extension “.amlx”.
A descriptor comprises up to five kinds of files (see Figure 6). It contains a Descriptor manifest file and Information Model file(s) and can contain attachment files, embedded Descriptors, or Common Services .
Figure 6 – Organization of the files in a Descriptor
The Descriptor manifest contains metadata information such as an identifier, a version number for the content and a version number for the format.
The Information Model files contain AML representations of UAFX Information Models.
Attachment files contain information useful for understanding and using the AutomationComponent in engineering, operation, or another phase of the AutomationComponent life cycle. This information can be considered supplemental to the information from the Information Model files. There is no specific format required for these files – these could be PDF, XML, image files, certificates, or even software binaries (e.g., for firmware updates).
Embedded Descriptors are useful for including information that is available in other Descriptors. For example, product-specific information could be available as a Descriptor created by the AutomationComponent vendor and embedded in a Descriptor created by an engineering tool.
Common Services files support the organization of the Descriptor content as specified by the Open Packaging Conventions standard. The Common Services can also be vendor-specific. They describe the file types present in the AML Container, the relationships between files, and the digital signatures.
A Descriptor has one or more Root AML Files. Root AML Files are the entry points from where engineering tools can parse and browse the content. The path of a Root AML File can be found by looking up a special Open Packaging Conventions relationship in the package relationship file of the Descriptor. This is explained further in 7.4.
More than one Root AML File can be used, for example, if more than one AutomationComponent is defined in a Descriptor.