This article describes the use of annotations to document our database objects in Oracle database 23c.
What's the Point?
We can think of annotations as an extension of database comments. With comments we were able to add free text to objects such as tables and columns, allowing us to describe their purpose and usage. Annotations take this a step further, allowing us to associate name-value pairs to most database objects, which can be used to describe or classify them. The names and values are free text, so we can pick anything that is meaningful to us.
You may see annotations described as "application usage annotations". This simply emphasizes that annotations are mean to help the documentation of your application.
Using Annotations
If an object supports annotations, the annotations clause typically follows this format.
ANNOTATIONS ( {ADD|DROP} annotation_name {'annotation_value'} {,} )
Here is a simple example of adding annotations to a table. Notice we don't use the optional ADD keyword while adding these annotations.
create table fruit (
id number annotations (SurrogateKey, UI_Display 'Fruit ID', Classification 'Fruit Info'),
name varchar2(50) annotations (UI_Display 'Fruit Name', Classification 'Fruit Info'),
description varchar2(50) annotations (UI_Display 'Description', Classification 'Fruit Info')
)
annotations (UI_Display 'Fruit Table', Classification 'Fruit Info');
Let's look at each in turn.
◉ SurrogateKey: This annotation tells us the column is a surrogate key. Notice this annotation has no value, as the name is sufficient to provide meaning.
◉ UI_Display: This annotation gives the preferred display name in any UI.
◉ Classificaton: This annotation allows us to classify the type of information present. In this case we classify it as "Fruit Info".
Remember, all these annotations are just free text we have made up. They have no meaning to the database or any tool other than the meaning we associate with them. If we need spaces in the key names we must double-quote them. This is true of reserved words also.
We can modify the annotations by adding or dropping annotations. In these examples we add a new annotation to the table without using the optional ADD keyword, we drop the annotation using the DROP keyword, and we add it again, this time using the optional ADD keyword.
alter table fruit annotations (Visibility 'Everyone');
alter table fruit annotations (drop Visibility);
alter table fruit annotations (add Visibility 'Everyone');
We can do a similar thing with the column level annotations.
alter table fruit modify (id annotations (Visibility 'Hidden'));
alter table fruit modify (id annotations (drop Visibility));
alter table fruit modify (id annotations (add Visibility 'Hidden'));
Views
There are two main views associated with annotations. They are the USER_ANNOTATIONS and USER_ANNOTATIONS_USAGE views, but you will probably only use the USER_ANNOTATIONS_USAGE view.
set linesize 150
column object_name format a12
column object_type format a12
column column_name format a12
column domain_name format a12
column domain_owner format a12
column annotation_name format a14
column annotation_value format a20
select object_name,
object_type,
column_name,
domain_name,
domain_owner,
annotation_name,
annotation_value
from user_annotations_usage
order by annotation_name, annotation_value;
| OBJECT _NAME |
OBJECT _TYPE |
COLUMN _NAME |
DOMAIN _NAME |
DOMAIN _OWNER |
ANNOTATION_NAM | ANNOTATION _VALUE |
| FRUIT | TABLE | ID | CLASSIFICATION | |||
| FRUIT | TABLE | DESCRIPTION | CLASSIFICATION | |||
| FRUIT | TABLE | NAME | CLASSIFICATION | |||
| FRUIT | TABLE | CLASSIFICATION | ||||
| FRUIT | TABLE | ID | SURROGATEKEY | |||
| FRUIT | TABLE | DESCRIPTION | UI_DISPLAY | |||
| FRUIT | TABLE | ID | UI_DISPLAY | |||
| FRUIT | TABLE | NAME | UI_DISPLAY | |||
| FRUIT | TABLE | UI_DISPLAY | ||||
| FRUIT | TABLE | VISIBILITY | ||||
| FRUIT | TABLE | ID | VISIBILITY |
11 rows selected.
SQL>
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