Hard references to database objects, Synonyms and ETL

1. Any time hard references are made to a database object it is an invitation to trouble. Especially in ETL where the object (table /view /procedure) can belong to schema.

2. Oracle has –> Database server name –> Schema –> Object

3. SCHEMA_NAME.TABLE_NAME is a bad way of referencing objects from the ETL architecture point of view as well as from data warehouse architecture point of view. The reason being any hard coding of the objects will cause trouble when they are moved from one schema to another.

4. An alternative could be to log in with the same SCHEMA_NAME where the objects exists.  But this will create a security hazard.  As ETL processes in will be in the same schema as that of the data warehouse structures and processes.

5. Also refereeing a object directly can also be issue because if the table name is changed or the column name is changes it will result in immediate code change.

6. Much argument can made that it’s not really an issue but just a little work or little more work. But what most people don’t understand is it is not how much work but when this work can come up. Most likely when you are migrating/ production run, or when the team is really at short of time.

7. Hard coded references also reduce flexibility… what if ETL wants to read data from some other schema to test an ETL process? What then?

Ok! What’s the solution then… 



A better way would be to have a dedicated schema for ETL user. And all the objects tables /views /procedures can be references by public synonyms. This way any object can be replaced by a new reference, temporary object, view or private synonym without; ever changing the code. It’s a much better way there are many more advantages but of course there will be more maintenance.

NOTE: This post is applicable to all etl tools or databases like Informatica, DataStage, Syncsort DMExpress, Sunopsis  or Oracle, Sybase, SQL Server Integration Services (SSIS)/DTS, Ab Initio,   MS SQL Server, RDB, etc.

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