Once a remote application has gone through the startup synchronization process (as described in Startup Synchronization), and the application files and data are synchronized on both the server and client workstations, it is important to keep the application files and data current. VTS does this by employing a locking scheme that is controlled using the Remote Configuration dialog – a VTS tool that assists you in the online configuration of remote applications.

 

The Remote Configuration dialog ensures that client workstations running a remote application can make changes to the application's files, pages, and tags without having one user overwrite everyone other user’s modifications.

In the remote configuration system, each of the application's files, pages, or tags is referred to as a "resource item”.  Changes made to any resource item using the remote configuration dialog and the locking scheme are known as “configuration changes”. Changes that do not involve the locking scheme are referred to as "operational changes".

 

In order to allow a client workstation to make a configuration change to a resource item, VTS must ensure that no other workstation can make changes to the item at the same time so that data is not lost.  To do this, the first client workstation to attempt to make changes to a resource item must obtain a lock on it. Some locks are obtained automatically when a user attempts to make a change to a resource item.  Other locks are obtained manually when an operator uses VTS's Remote Configuration dialog to lock a specific item, usually before editing it outside the VTS user interface.

 

In either case, once a resource item has been locked by a client workstation, all other workstations on the network are kept informed of the lock, but no other workstation can make changes to the resource until the lock is removed. Locks are removed either by the client that holds the lock, or by another client who forces release of the lock.

The following types of change will cause VTS to automatically lock a resource item:

•    Drawing an object on an application page locks the page;

•    Manipulating a page's properties through the Configure dialog locks the page;

•    Modifying a tag's properties locks the tag;

•    Manipulating a tag through the Tag Browser locks the tag;

•    Manipulating the Page Menu through the Menu Editor locks the menu;

•    Making offline changes to the tag properties database locks the modified tags when the application is run; and

Additionally, clicking the Lock Item button in the Remote Configuration dialog locks a selected resource item.

 

VTS's Remote Configuration dialog stores locking information using the configuration database (see Configuration Database (Config.db).  It should be noted here that the configuration database cannot be manually edited – it is used by VTS exclusively, to handle the remote configuration locking scheme.