Database modernization entails the migration of hierarchical data structures (IMS/DB (DL/I)), data and logic to a relational database system (e.g. SQL DB2, Oracle, etc).
Converting an organization's database from hierarchical brings with it many advantages including cost, stability and efficiency. Ensuring applications continue to function is one of the key questions which needs to addressed.
Other advantages include:
Traditionally, databases were built based upon hierarchical models consisting of segments. Each segment had a "Parent" and "Children". Where the parents can have many children, each child can have only one parent there is only one route to and from that child. IMS/DB is based upon the hierarchical database.
Following is an excerpt of an employee hierarchical database, where each employee is a segment, containing attribute fields such as department, qualification level and personal data. On the other hand, Relational Databases (e.g. Oracle, SQL and DB2) have flat structures, enabling each attribute to have a multitude of relationships. In the same example, the Employee master table, is complimented by tables listing the attributes. Each employee, department and qualification have their own dataset and the tables are linked by through common ids (hence relational).
Many organizations are embarking on project to move to relational databases - the challenge is to preserve the considerable investment made to date.
The migration of IMS/DB to a relational environment requires three main steps.