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DataServer for Oracle
Introduction : DataServer components : The schema holder

The schema holder

The schema holder contains information about the data definitions for one or more Oracle databases, or from any other data manager supported by the OpenEdge DataServer for Oracle architecture. The schema of a database is a description of its structure, the tables, the fields within the tables, the indexes, stored procedures, and other objects. That information in the schema holder is called the schema image. When you use an OpenEdge client with an Oracle database, the DataServer uses the schema image to translate OpenEdge database requests into a format that can be used to access the data in the Oracle database.
The schema image contains all the database information for developing an OpenEdge application for the DataServer, which lets you develop and compile applications for an Oracle database without being connected to it.
OpenEdge accesses the schema holder only when it compiles procedures and at the beginning of a run-time session for schema caching. Schema caching occurs when data definitions are loaded into memory. Typically, the schema holder is idle during a run-time session after the initial schema caching.
Before an OpenEdge client can access Oracle data, you must create a schema holder and load the Oracle database definitions—the schema image—into the schema holder. Then you can use the Data Dictionary to add OpenEdge database features, such as validation expressions or messages.
The following figure illustrates the schema-loading process.
Figure 3. The schema-loading process