Oracle Synonyms 

Administration and Creation of Synonyms

Synonyms are a very powerful feature of Oracle and other SQL-compliant relational database systems. They are used as a database shorthand. They make it possible to shorten the specification of long or complex object names. This is especially useful for shared tables or views. In addition, the use of DATABASE LINKS in synonyms allows transparent access to other databases on other nodes or even other entire systems halfway around the globe.

Synonyms are created using the CREATE SYNONYM command. Synonyms can be either PRIVATE (the default) or PUBLIC. Private synonyms can only be used by the user creating them. You must have a specific grant or one of the special ROLES assigned to you before you can create synonyms. Only users with appropriate privileges (usually DBAs) can create PUBLIC synonyms. Since only the owner can use them, PRIVATE synonyms are more secure.

Monitoring Synonyms Using the V$ and DBA_ Views

Synonyms remain the same in Oracle8, Oracle8i, and Oracle9i. The major changes that have affected Oracle synonyms are those to the structure of the connection strings from SQL*NET V1 to V2 to NET8. Despite the fact that synonyms are the key to providing cross-database access for queries, and a means of implementing distributed data across nodes, systems, and databases, in all the reports reviewed for this book, not one seemed to cover synonyms. Recall that a synonym allows a shorthand version of an object name to be specified. The parts of a synonym are the object name (which usually includes an owner) and, possibly, a database link that will also provide an Oracle user name and password to a remote system. A complete report will show all of these items.

Why is it important to monitor Oracle synonyms? Oracle synonyms can be used to access data, sometimes data that shouldn’t be accessed if object grants have been too widely granted. In addition, they are the means for reaching other nodes and databases. If a connect string becomes invalid, a user name is disconnected or its password changes or node name changes, it is good to be able to see which object synonyms will be affected.

You may also want to create private synonyms for the objects you are going to replicate with the create synonym command. You can use this command to create private Oracle synonyms as seen in this example:

CREATE SYNONYM my_tab FOR tab_own.my_tab;