2.5.2 Schemas
A schema is a logical concept that includes tables and indexes. Each HADB user can own a single schema only. Elements that can be defined in a schema are called schema objects.
In HADB, a user (the HADB user with the authorization identifier that was used for the current connection to the HADB server) can define schema objects only in a schema which that user owns. He or she cannot define schema objects in schemas owned by other HADB users.
The following figure shows the concept of schema.
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![[Figure]](GRAPHICS/F0000026.GIF)
The following lists the schema objects that can be handled in HADB.
- ▪ List of schema objects
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Base table
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Viewed table
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B-tree index
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Text index
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Range index
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HADB manages the definition information for tables and indexes in tables that are called dictionary tables. It also manages the cost information and chunk information for tables and indexes in table format. These tables are called system tables. Once HADB's initial setup has been completed, a schema (called the MASTER schema) that owns the dictionary tables and system tables is created automatically.
The name of a schema is called a schema name. One schema name is assigned to each HADB user. A schema name uniquely identifies a group of tables and indexes in the HADB database.
In HADB, the user ID (authorization identifier) that identifies an HADB user who is accessing the HADB server is the same as that user's schema name.