In an Oracle database, a schema is a collection of logically related database objects such as tables, indexes, views, etc. The schema can be further divided into logical schema and physical schema.
A logical schema is a conceptual view of the entire database or a subset of the database. It defines how data is organized and how the data is related to one another. It is represented by a data model, which describes the structure of the database and the relationships between the database objects. A logical schema is independent of any specific physical implementation.
On the other hand, a physical schema is a representation of the logical schema in terms of files and indexes on disk. It describes how the data is stored, accessed and managed on the physical storage devices such as hard disks, SSDs, etc. A physical schema is specific to a particular database system and its implementation.
To illustrate the difference between a logical schema and a physical schema, let’s consider an example of a simple ecommerce database. The logical schema for such a database may include tables such as Customers, Orders, Products, and Suppliers. The relationships between these tables may be represented using a data model such as an Entity-Relationship (ER) diagram.
The physical schema for the same ecommerce database may comprise of actual data files containing the data of the tables, indexes for these tables, and configuration parameters that specify how the database engine interacts with the storage devices. The storage devices themselves may include hard disks, SSDs, or other storage media.
In summary, the logical schema defines the concepts and relationships between the data, while the physical schema defines how the data is stored and accessed on disk. Understanding the difference between these two is essential for efficient and effective database design and administration.