JIRA stores its configuration and data in a database; if you are evaluating JIRA, it's possible to use the embedded Hyper SQL Database (HSQLDB) written in Java. This is suitable for small applications, and JIRA uses it only in its evaluation version. HSQLDB is not recommended for production usage. For that, JIRA recommends MySQL or PostgreSQL.
No matter what type of database is used, the database schema that is, the tables and the relationship between them, is the same. If you want to take a look at the schema, you can refer to JIRA_INSTALL/atlassian-jira/WEB-INF/classes/entitydefs/entitymodel.xml
.
The contents of the file are as displayed in the following screenshot:
This is an XML file that contains the definition of all the tables in JIRA and their relationship with other tables.
Alternatively, you can also check the database schema on the Atlassian website, at https://developer.atlassian.com/display/JIRADEV/Database+Schema.