异构数据库的数据迁移

Microsoft Access（.mdb）数据库的数据迁移：

Microsoft Access Architecture:

Forms	Reports	Basic
Jet DBMS Engine

 

<------->

.mdb file

Microsoft Jet database engine handles updates by multiple users by using optimistic and pessimistic locks.

Using pessimistic locking,Microsoft Jet database engine places a hard lock on the data page that contains the row being edited. Other users cannot start editing the lock row until the lock is abandoned or the changes are written to disk.

Microsoft Jet database engine employs an optimistic locking scheme when working with Oracle. An optimistic locking scheme does not place a hard lock on the source tables.Instead,when you want to commit a change,Microsoft Jet database engine checks to make sure that another user has not modified the data before it posts the change.

Oracle databases are powerful,flexible,and scalable relational database management system(RDBMS) servers that run on a ranger of computer system,from personal computers to largest mainframes.Oracle is designed to run effectively in a client/server enviroment and supports hundreds to thousand of users.

The Oracle architecture supports advanced server features,such as record locking with version references,(not page lockingas provided by Microsoft Access),advanced query optimization,the PL/SQL programming language,data replication,distributed database management,and other important features.

Triggers and Stored Procedures:

Oracle allows you to wrte and store code in the DBMS along with data.You can associate trigger code with an Update,Insert,or Delete event for each row or for an entire table.You can also set a trigger to run before an event or after an event.For example,you can set a trigger to run after a row is updated.

A stored procedure is a general routine,either function or subroutine,that is stored in pre-compiled form on the server.A trigger may call stored procedures,but triggers are only activated by specific database activity,such as the insertion of a row in a table.

Forms	Reports	Basic
Jet DBMS Engine			<---->	Oracle Database
		ODBC
.mdb file