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5.1
Rewriting
This approach requires the entire database system be redeveloped from scratch in a
relational format. One must translate the nonrelational schema into relational sche-
ma, rewrite all the application programs to run on the relational database, and throw
away the old application programs.
5.2
Software Interface
Vendors may provide relational interface software to their nonrelational database
management systems (DBMSs). For example, logical record facility (LRF), a soft-
ware tool from Computer Associates (CA
1992a
), is a run-time facility that allows
application programs to access IDMS (a network database) data without knowing
the physical structure of the database. It converts IDMS into IDMS/R, a relational-
like database. Under LRF, programmers do not use database navigation statements
to access the database. It is possible to combine processes in a macro that acts like
a relational DML statement. Views are defined by the relational operators select,
project, and join. A view is implemented as a logical record. Figure
5.1
shows a
diagram of the processing retrieval paths of LRF.
As an example, to implement a join operation for three records (Department, Of-
fice, and Employee) in a company's network database, using the foreign key, Em-
ployee-ID, the database administrator (DBA) must define the paths table as shown
in Fig.
5.2
(CA
1992b
). Only after this table has been defined in the subschema can
the user retrieve the rows from the results of the join operation.
A logical path EMP-LR using LRF is defined in subschema below:
Step 1- Logical-Record
Request
Step 2- Logical-Record
Path
LRC
BLOCK
LRF
SUBSCHEMA
Step 6 - Path
Information
data items
Program
Variable Storage
Step 3 - Database Request
(path statement)
Step 5 - Database
Response
DBMS
IDMS/R
DATABASE
Step 4 - Database
Retrieval
Fig. 5.1
LRF processing retrieval path (step 3, 4, 5 are repeated until all path-DML statements
have been executed)
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