New Replication Options in Access, Oracle, and Notes

Rick Dobson

The new 32-bit version of Microsoft's Access for Windows 95 database, which is slated to ship this fall, offers a host of new features. But one that should especially appeal to developers supporting remote workers is replication. Made popular by Lotus Notes and introduced for enterprise databases, such as Oracle 7, replication allows Access 95 users to work remotely with a copy of the master database and later incorporate all their changes into the master database.

Based on use of a beta version of Access 95, the easiest way to use the database's replication is through the Windows 95 Briefcase. Making a database replica is as easy as dragging and dropping a database file from a server into the Briefcase of a noteb ook PC that's docked to your network.

Because Windows NT 3.51 does not have the Briefcase interface, users of that OS (as well as Windows 95 users) can control Access replication in two ways: by using the Tools, Replication menu , which provides commands for controlling replication, or by using Visual Basic for Applications, which replaces the Access Basic programming language used in older versions of Access.

Dropping a database file into the Briefcase of a connected portable computer initially creates a regular replica and a design-master replica. The regular replica is used for updating data changes. Database developers use the design-master replica to propagate database-design changes to other replicas.

Access 95 offers replication management tools and automatic conflict resolution. But these tools don't offer quite the level of granularity that other programs, such as Lotus's (Cambridge, MA) Notes 4.0 and an upcoming version of Personal Oracle 7 from Oracle (Redwoo d Shores, CA), do.

Conflict resolution in a replication is the process of reconciling changes to two replicas that are inconsistent. If, for example, in one replica a customer's Bill To address changes, but in another replica the Ship To address of the same record changes, the two records conflict when they're synchronized at the record level.

Access's approach is to assign a "winner" based on which record has changed most often. If both have changed equally often, Access picks a winner randomly. This is in contrast to Personal Oracle 7 for Windows 95, slated to ship this fall, which will be able to take advantage of 10 preprogrammed rules for replication-conflict resolution that are included in Enterprise Oracle. Enterprise Oracle also enables the database developer to write custom conflict-resolution rules.

Unlike the previous version of Personal Oracle 7, which only let you replicate with a server in publish-and-subscribe (aka read-only) mode, the new version will support full symmetric r eplication to let it bidirectionally replicate with the large, mission-critical databases typically developed using the Enterprise Oracle database management system. Access 95 will not directly replicate with Microsoft's SQL Server database, however, officials at Microsoft say that capability might be added to a future version of Access.

Replication Manager, which will be released with the Access Developer's Toolkit, adds functionality and simplifies management. This Access component permits the scheduling of replication for particular times, such as 3:00 a.m., and the setting of synchronization rules for the sequence of replication among replicas. It also provides a "dropbox," a network location for holding replica updates. When replicas become connected to the network, they can update themselves with the dropbox contents.

But neither Oracle nor Microsoft supports field-level replication, which is promised for Notes 4.0, the Lotus groupware platform that's now slated for availability in the four th quarter of this year. Field-level replication accelerates synchronization by reducing the amount of data that's passed in a replication.

For instance, if one field changes in a record (which is actually a document in Notes), then, instead of the whole document being passed in the replication, just a single field is passed. Field-level replication's increased efficiency bodes well for administrators who manage worldwide Notes networks.

Desktop users will have a rich array of replication options available in the fourth quarter of this year. Access 95 provides this functionality to a whole class of department-level developers. Personal Oracle tightly integrates with Enterprise Oracle to deliver some of the rich functionality of its flagship product. Lotus will reduce the time needed to replicate databases with Notes 4 when it rolls out field-level replication.

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Access 95

GOOD FOR:



--  Letting mobile workers
 periodically synchroni
ze their remote
    databases with the home-office version.


--  Letting small businesses
 synchronize database replicas
    across a few offices.


--  Database administrators
 who want to balance the load on a
    database by directing users to replicas.


--  Developers who want
 to distribute design updates
    through Access replication.


--  Database backup
 (only changes are replicated).


BUT NOT FOR:



--  Replicating Access 95
 data directly with Microsoft's SQL Server.

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It Won't Replicate New Computers, But Your Files Will be in Great Shape

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In Access 95's Tools, Replication menu, the items in black-on-gray are for managing replicas after a database is converted to a design-master replica. The options in gray list selections for converting a database to a design-master replica and recovering from a faulty design-master replica.