JSON schema semantics

JSON schema semantics:

1. $ref: Foreign keys
2. _primary_key: If true indicates that the data item is a primary key
3. type: Indicates the type of data (string, integer, number)
4. examples: Examples of the data item (shown while hovering on column name)
5. description: Description of the data item (shown while hovering on column name)
6. rcsb_description: Same as description; redundant
7. attribute_groups: Group together data items that form composite keys. The id and labels within the attribute groups differentiate the multiple instances of the composite foreign keys. These are used along with $ref.
8. enum: Controlled vocabulary of allowed values for a data item
9. rcsb_enum_annotated: Same as enum; redundant
10. required: List of mandatory data items in a table

Each table has a structure_id data item that points to the entry_id, which is the PDB accession code.

The JSON schema is generated from the IHM-dictionary. This is an extension of the PDBx/mmCIF data dictionary.