How do Catalogs, Schemas, Users, and Database Instances Relate in Different Database Vendors?

Understanding the Relationships between Catalogs, Schemas, Users, and Database Instances

Identifying database objects across different database vendors can be challenging due to varying terminology and object definitions. This article provides a comprehensive overview of these concepts in the context of Oracle, SQL Server, DB2, MySQL, and PostgreSQL.

Identifying Objects Uniquely

For Oracle, an object can be identified using the schema name and object name. In PostgreSQL, a database name is also required, while in MySQL, only the database name and object name suffice. SQL Server requires the database name, owner, and object name.

Abstraction of Data Storage

A catalog is an abstraction of data storage that organizes and manages the logical structure of a database. It typically provides metadata about the database's objects and their relationships.

Vendor-Specific Implementations

Oracle:

• Database = Catalog
• Schema = User Account
• User = Schema Owner

PostgreSQL:

• Database = Catalog
• Schema = Namespace within Database
• User = Account with Access to Databases

MySQL:

• Database = Schema = Catalog
• User = Account with Access to Databases

Microsoft SQL Server:

• Database = Namespace Qualifier
• Schema = Owner
• User = Account with Access to Databases

Conclusions

• Identifying database objects requires understanding the vendor-specific definitions of catalogs and schemas.
• A catalog is indeed an abstraction of data storage, although its meaning can vary across databases.
• While databases and schemas have common definitions, catalogs can have varying interpretations.
• Schemas are particularly useful for organizing database artifacts and managing access control.

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