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Joined Tables and Extension Tables of Business Components

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Not every table used by a business component is a base table. In addition to columns from the base table, columns may also be included from joined tables and extension tables. For further information on tables see chapter on Using Extension Tables and Columns.

Joined Tables

A joined table provides rows on a one-to-one basis to the business component as a result of a foreign key relationship between the joined table and the business component's base table. That is, for every record in the business component (which corresponds to a row in the base table) there can be a corresponding row in the joined table. However, not every record in the base table will have a record in the joined table.

The data obtained by a business component through a join (other than to an extension table) is read-only in that business component.

The use of fields from both the base table and joined tables is illustrated in Figure 83.

Figure 83. Fields from the Base Table and a Joined Table

Using the contact example, most contacts belongs to an account. Account information is stored in another table, S_ORG_EXT. The account is uniquely identified in each contact record (S_CONTACT row) by means of a foreign key, the Account Id field (the PR_DEPT_OU_ID column). A join uses these relationships to make account data columns available to the Contact business component for each contact. This is illustrated in Figure 84.

Figure 84. Fields from a Joined Table

Extension Tables

Extension tables are a special kind of joined table. Like other joined tables, extension tables provide rows on a one-to-one basis in parallel with base table rows. Extension tables are identified by the _X suffix in the table name, such as S_ORG_EXT_X, which extends S_ORG_EXT.

Extension tables are provided specifically to allow columns to be virtually added to a base table rather than physically added. This provides the means to expand base tables without violating DBMS or database design restrictions, and without the need to perform complicated database restructuring operations. Extension table data, unlike the data in other joined tables, can be updated in the business component.

Extension tables are discussed in greater detail in Extension Tables.

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