Data Conversion - Information Systems Reengineering, Integration and Normalization - page 147

hierarchical database to a relational database, and from a relational database to an
object-oriented or XML database.

4.5 Data Conversion from Network to Relational

As described before, the logical approach consists of an unload step and an upload
step. For the purpose of automation, we must convert data from a network database
to a semantically richer relational database. The primitive semantics of record types
and record keys in network schema can be mapped into relations and relation keys
in relational schema. Other more advanced semantics such as generalization and
categorization are not considered the main component of the database and can be
handled later. Thus, a preprocess of direct schema translation from network to rela-
tional is needed before the data conversion. These steps are shown in Fig. 4.7 (Fong
and Bloor 1994 ).
Conversion is automated by database navigation. The process includes unload-
ing the network database into sequential files. The unload process reads all the
records of the network database, and writes them to the files.
The procedure to convert the network database into relational is:
Preprocess step 1—Direct schema translation from network to relational.

• Rule1.Mapeachrecordtypetoarelation.
• Rule2.Mapeachrecord“Navigational”key(i.e.,concatenateownerrecordkey
to member record key) to the relation key.

The translated relational schema will then be used as a template to map the network
database content to a target relational database.
Step 1—Create a template file to define the network database and its translated
relational schema.

network
database
template

relational
schema

(optional)

Unload
process

Upload
process

Ta rget
sequential
files

Transfer

Network
database

sequential
files

Relational
database

Fig. 4.7 System flow diagram for data conversion from network to relational