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Recursive Data Relationships

Oracle Tips by Burleson Consulting

The Data Warehouse Development Life Cycle

Oracle Data Warehouse Design

Dealing With Recursive Data Relationships

Clearly, we compound the problem of recursive relationships by adding this additional construct--namely, a class hierarchy (see Figure 4.12). Unfortunately, these types of challenges are very common. While it is true that "parts are parts," the different parts have subtle variations, leading to different data items depending on part type. For example, a food-related part might have a shelf_life column, but that column does not apply to a nonfood-related part. The class hierarchy design in Oracle tables is covered later in this chapter.

Figure 4.12  A recursive many-to-many relationship with the addition of an IS-A hierarchy.

With an understanding of the nature of recursive relationships, the question becomes one of implementation--What is the best way to represent a recursive relationship in Oracle and navigate the structure?

The following Oracle table definitions describe the tables for the part-component example:

   part_nbr     number,
   part_name    varchar2(10)
   part_desc    varchar2(10),
   qty_on_hand  number); 

   Has_part     number,
   Is_a_part    number,
   qty          number);

Look closely at the COMPONENT example. Both the Has_part and Is_a_part fields are foreign keys for the part_nbr field in the PART table. Therefore, the component table is all keyed except for the qty field, which tells how many parts belong in an assembly. Look at the following SQL code that is required to display the components in a Big_Meal:

SELECT part_name

This type of Oracle SQL query requires joining the table against itself. Unfortunately, because all items are of the same type (namely, PART), no real substitute exists for this type of data relationship.

This is an excerpt from "High Performance Data Warehousing", copyright 1997.
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