Web Messenger: The Basics
Web Messenger is a notification system that sends information in the form of packaged messages from Vernon CMS to another application, such as your online collections website or digital asset management system. Messages are generated when changes are made to records, enabling you to update records in other applications in real time.
In the case of Vernon Browser, Web Messenger generates messages when data changes are saved to records in the Object, Person and Photo/Audio-Visual files. Vernon Browser acts as the listener, then reads these messages and updates the records that have previously been exported to Vernon Browser.
Things to consider about Web Messenger
oTo make use of Web Messenger, you must be using Vernon Browser version 2.0.9 or later
oWeb Messenger does not replace the Browser Export. Initial content will still need to be exported using the Browser Export tool and not Web Messenger. Web Messenger only captures changes to the Object, Person and Photo/Audio-Visual files. You may need to use the Browser Export tool to update changes made to records in other authority files, such as Place.
oWeb Messenger allows you to update Vernon Browser in 'realtime'. Once a record is saved, the changes are immediately recorded in messages and placed in the queue for processing. This means that the Browser records could be updated and the new information made available online before you have a chance to catch any mistakes in data entry.
Other Components
The Packager
oThe packager is a program in Vernon CMS which handles communication between Vernon CMS and the Listener.
oWeb Messenger posts individual messages in a queue so that they can be processed. The packager takes the messages that have been processed in the queue and puts them together in a way that the listener can understand.
oThe packager is specific to the listener, and is specified in the Web Messenger Configuration window.
The Listener
oThe listener can be any application that can receive the messages from Web Messenger.
Web Messenger: The Details
oEach time you save a change in the Object, Person or Photo/Audio-Visual files, Web Messenger captures that change as a message. Capturing can take place on multiple workstations, and is not limited to a particular user or group of users. Generally, the capturing function can be left on so that changes are registered as they occur.
oOnce a message is captured, it is placed in a queue. Queues help to control the volume of messages and they manage the messages if there is a problem with the listener. If the listener is not working, or can't accept the messages for some other reason, the messages will remain in the queue until they are able to be processed.
oQueues can be processed in two ways, synchronous and asynchronous. The queue for Vernon Browser processes messages in asynchronous mode.
oIn the synchronous mode, the order of transaction messages is important as the listener is looking for a particular change in a particular field. A message is created each time a record is saved and the messages are processed in the order they are placed in the queue.
oIn the asynchronous mode, the order of saved changes does not matter. All that matters is that there has been a change to a record and the whole record needs to be updated on the listener. The listener only needs one message per record detailing any change in order to prompt it to update that entire record. Therefore, only one message per record will be posted in the queue. Subsequent messages for the same record are ignored because the listener already knows to update the record with the most recent data.
oAfter processing the queues, Web Messenger then sends the messages, via the packager, to the listener. Sending can only occur on workstations that have been set up as Web Messenger Servers. Not all users need to be able to send messages and communicate with the listener. Sending can be managed by supervisor workstations or an Indexing machine, if applicable. The sending function should be turned off when the listener is down, such as when maintenance is being performed on the Browser.
oThe listener reads each message and checks if it is relevant to its data. If the message is relevant, the listener updates its data according to the message. If the message is not relevant, for example if it applies to a record that has not been exported to Vernon Browser, the listener will ignore it.
