Information Technology Reference
In-Depth Information
Orignal
network
program
Original
relational
program
Network
DDL
NETMAP
RELMAP
Generated
network
program
Generated
relational
program
Incremental
file
Network
DBMS
Relational
DBMS
Fig. 5.4
Incrementally converting network to relational database system
program reads the data in the temporary file and inserts them into the relational
database.
At the network site, DML statements that update the database are monitored.
Every time an update operation changes the database, the changes are also recorded
in the differential file. This transformer is referred to as NETMAP.
At the relational site, all DML statements are monitored. Before a retrieval oper-
ation retrieves data from the database or an update operation changes the database,
all changes recorded in the differential file, but not yet installed in the database, are
first installed in the database. This transformer is referred to as RELMAP.
5.6
Adding a Relational Interface to a Network Database
Emulation adds more workload to the DBA because of the pre-compile macro call
design of each database access. Decompilation is not feasible because of the na-
ture of reverse engineering from lower level to higher level database management
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