Introducing JSON schemas for OCA
If you have been already using the Semantic Engine to write your schemas you will have come across the .zip schema bundle. This is the machine-readable version of your schema written in JSON where each component of you schema is a separate file inside a .zip folder.
Overlays Capture Architecture has transitioned now to a schema package that has the same content with a few extra pieces of information and a new way to extend the functionalities of schemas. First, rather than each component of the schema being in a separate file inside a .zip, they are listed one after another inside a single .json file. The content of each schema component is the same and exists as the schema bundle. We found .zips were a problem for our Mac users especially and they were also challenging to include in repositories. The change to a single JSON object will address these challenges.
Second, ADC has extended the functionality of OCA to cover use cases that aren’t included in the original specification such as attribute ordering. These extra overlays follow the same syntax and structure of OCA and are in a second object called extensions. Both the OCA bundle and its extensions are included in a JSON file called OCA Package. You can read more about this update on the OCA Package specification.
Because OCA uses derived identifiers, this structure means we can give a derived identifier to the OCA Bundle which contains standard, well specified overlays. We also give researchers and developers flexibility to add their own functionalities via the OCA extensions where new additions won’t change the core bundle derived identifier. Finally, the entire OCA Package is given a derived identifier thus binding all the content together. When you reference your OCA schema you should use the Package identifier.
One of the first extensions we have added to an OCA schema is the ability to keep ordering of attributes. You may have noticed that in an OCA schema all the attributes are ordered alphabetically. Now with the ordering overlay we support user-entered ordering and this functionality is included now in all Semantic Engine tools.
The Semantic Engine can continue to consume and use .zip schema bundles but now the default will be to export .json schema packages. The .json packages will continue to be developed and so if you are using any .zip schema bundles you can open them using the Semantic Engine and export them to obtain the .json version.
Written by Carly Huitema
