Release 10.1A: OpenEdge Getting Started:
Database Essentials

Database schema and metaschema

The logical structure of the OpenEdge database consists of the elements of a relational database that you just read about: tables, columns, and indexes. The description of the database’s structure, the tables it contains, the columns within the tables, views, etc. is called the database schema or the data definitions.

The underlying structure of a database that makes it possible to store and retrieve data is called the metaschema. That is, the metaschema defines that there can be database tables and columns and the structural characteristics of those database parts. All metaschema table names begin with an underscore ( _ ). The metaschema is called the metaschema because it is data about the data.

Note: The metaschema is a set of tables that includes itself. Therefore, you can do ordinary queries on the metaschema to examine all table and index definitions, including the definitions of the metaschema itself.

The physical structure of the database and its relationship to the logical structure is discussed in Chapter 3, " OpenEdge RDBMS."