Ewan a while ago remarked that the receipted delivery of messages which
X400 gives is achievable by applications, and therefore X400 is not
necessary.

Part of my background research produced the example below.

Sounds a useful approach for laptops, branches, and other EMR
applications, does it not.
------------

SQL Anywhere has replication functionalilty built into it. One then
applies that functionality when creating a distributed database. See
below for key points that we used in a demonstration some while ago.
<name> can give you chapter and verse if you need it.

<name>

Replication Facilities
Sybase SQL Anywhere provides built-in facilities for data replication
between a consolidated (or master) database and one or more remote
databases. The consolidated database contains all the data to be
replicated. Remote databases may contain all the data or may contain
just some of the data. Replication is two way:

- changes made at the consolidated database are replicated to remote
databases; while
- changes made at a remote database are replicated to the consolidated
database and thence to other remote databases.

Remote databases can contain data tables that are not present in the
consolidated database so long as these are not involved in the
replication. 

Inter-System Data Transfer
Sybase SQL Anywhere exchanges data between databases using messages
that can be transferred either by e-mail, for databases that have no
direct connection, or by direct file transfer. Recognising that e-mail
systems do not guarantee that messages will reach their destination nor
arrive in the order they were sent, the database system incorporates
protocols to guarantee that all replication updates are received and
are applied in the correct order. 

Database Integrity
Sybase SQL Anywhere incorporates robust methods for ensuring the
integrity of the distributed database. For example:

The relational database management system (RDBMS) maintains a record of
the current status of replication from the master to all subscriber
databases. This enables the software program that initiates
inter-system data transfers to be written so that it will also generate
a log file to report their outcome. 

The RDBMS contains a “guaranteed transmission mechanism”. The
replication process is bi-directional so that a receipt is sent for
each data transfer, corrupt files are detected and failures are
automatically re-transmitted.

Also, by replicating portions of its internal transaction log the RDBMS
ensures that database transactions (additions, updates, deletions) are
replicated atomically, i.e. either a whole transaction is replicated or
none of it is replicated.

These features ensure database integrity throughout the distributed
system.


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%