Database Management System Emulation - Information Systems Reengineering, Integration and Normalization - page 243

Frame model meta-data

OODB API

Object frame
model agent

SQL
gateway

API

Frame
model
constraint
class

OSQL 1
OSQL 2
:
:
OSQL n

SQL

Constraints
verification

Frame
mode
method
class

command OSQL

Call
methods

User

RDBMS

Method 1
Method 2
:
:
Method n

Methods
invoke Method

(stored
procedure)

Fig. 6.5 The architecture of OFMA (object frame model agent)

base system is defined as a loosely coupled federated database architecture using a
platform and vendor independent language and protocol. A standard OODBAPI is
needed to transform heterogeneous RDB systems to homogeneous object relational
database systems.

6.3.1 Object-Oriented Database Application Program Interface

Because of OODBAPI, users can issue OSQL to access each other's RDB via frame
model metadata. After schema mapping from OODB to RDB, OSQL query transac-
tion can be translated into SQL query transaction. The technique is to convert the
database access path from OSQL's navigational query graph to the SQL's relations
join query graph. As shown in Fig. 6.5 , the object frame model agent (OFMA) is
divided into three parts: the command scanner, the method interpreter, and the DML
interpreter. The server API process will first scan the incoming commands, identify
the kind of command: DML or Method. If the command is DML, the server API
will parse the DML command to the RDBMS. The execution and error checking
will be performed by RDBMS. The error or result set will be returned to the caller
after execution. If the incoming command is Method, the stored procedure defined
in the method class of the frame model will be invoked, and the error or result set
will be returned after execution is performed.