ODF Metadata API

ODF provides a very simple API for searching, retrieving, and (to a limited extent) for creating new metadata objects. This API abstracts away specifics of the underlying metadata store. See the REST resource metadata, e.g., here or look at the Java interface org.apache.atlas.odf.core.metadata.MetadataStore.

In this API we distinguish between MetaDataObjects and MetadataObjectReferences. Where the former represent an object as such, the latter is just a reference to an object. You may think of the MetaDataObjectReference as a generalized XMeta RID.

Simply put, metadata objects are represented as JSON where object attributes are represented as JSON attribute with the same name. Simple types map to JSON simple types. References to another object are represented of JSON objects of type MetadataObjectReference that has three attribute:

1. id: the object ID
2. repositoryId: the ID of the repository where the object resides
3. url (optional): A URL pointing to the object. For Atlas, this is a link to the object in the Atlas dashboard.

The API is read-only, the only objects that can be created are annotations (see section Data model and extensibility.

Here is an example: suppose there is a table object which has a name and a list of columns. The JSON of this table would look something like this:

{
   "name": "CUSTOMERS,
   "columns": [
                 {
                    "id": "1234-abcd",
                    "repositoryId": "atlas:repos1"
                 },
                 {
                    "id": "5678-efgh",
                    "repositoryId": "atlas:repos1"
                 }
              ],
   "reference": {
                  "id": "9abc-ijkl",
                  "repositoryId": "atlas:repos1"
                },
   "javaClass": "corg.apache.atlas.odf.core.metadata.models.Table"              
}

The reference value represent the reference to the object itself where as javaClass denotes the type of object (table in this case). The name attribute contains the table name where the columns value is a list of references to two column objects. These references can be retrieved separately to look at the details.