The Joins in BOBJ.
You have several approaches to creating joins in Business Object - Universe Designer:
- Tracing joins manually in the schema (Drag and drop)
- Defining join properties directly ( Menu Select Insert > Join )
Types of joins
You can define the following types of joins in Business Object - Universe Designer :
| Equi-joins in BOBJ |
(includes complex equi-joins)
|Link tables based on the equality between the values in the column of one table and the values in the column of another. Because the same column is present in both tables, the join synchronizes the two tables. You can also create complex equijoins, where one join links multiple columns between two tables.|
| BOBJ - Theta joins |
|Link tables based on a relationship other than equality between two columns.|
|BOBJ - Outer Join||Link two tables, one of which has rows that do not match those in the common column of the other table.|
|Shortcut joins||Join providing an alternative path between two tables, bypassing intermediate tables, leading to the same result, regardless of direction. Optimizes query time by cutting long join paths as short as possible.|
|Self restricting joins||Single table join used to set a restric tion on the table.|
Join path problem
A Semantic Layer - Join Path (or Query Path) is a series of joins that a query can use to access data in the tables linked by the joins.
Semantic Layer - Join Path (or Query Path) problems can arise from the limited way that lookup and fact tables are related in a relational database. The three major join path problems that you encounter when designing a schema are the following:
You can solve all these problems by creating BOBJ - Alias (a copy of a base table), BOBJ - Context (a defined join path), and using features available in Business Object - Universe Designer to separate queries on measures or contexts.
You can display primary and foreign keys in all tables in the Structure pane.
When you display underlined key columns, the information is stored in the .UNV file. This information is lost when you export a universe to the Central Management Server ( CMS ) (CMS) repository. You have to re-display keys for a universe, each time it is imported.
To display keys:
- Select Tools > Options. The Options dialog box opens to the General page.
- Click the Graphics tab. The Graphics page appears.
- Select the Underline Keys check box in the Columns group box.
- Click OK and you need to refresh the structure before key columns appear underlined.
- Select View > Refresh Structure.
What tables do not have to be joined?
You should join all tables in the schema that are inferred in the SQL generated by objects in SAP BO - Web Intelligence queries run against the SAP BOBJ - Universe. The only exceptions to these are the following types of tables:
- Base tables from the schema that have been aliased for each use. These are the original tables for which you have created aliases either for renaming, or join problem resolution reasons. These base tables are typically not used in any object definition.
- Tables that are the target of table mapping for Supervisor.
- Tables that are the target of aggregate awareness syntax (although this has to be taken on a case-by-case basis). For example the two aggregate tables in the sample efashion universe are not joined to any table in the schema.