Composite thinking

In the issue of the Lotus developerWorks newsletter that I received in my inbox today there is a link to an article on creating applications using the Property Broker of Lotus Expeditor (Creating collaborative components for IBM Lotus Expeditor Property Broker). This was kind of funny since it coincided with me receiving a Java newsletter with an article on using the PropertyChangeListener of the Java SDK.

For those not in the know, the Property Broker is the middleware which is used in the Lotus Expeditor framework to dispatch property change events between components and hence is the glue that makes the different components of a composite application work together. The Property Broker is configured either declaratively using an UI or using an API.

The approaches described in the two articles are quite similar and both describe how using a declarative approach (much like extension points in Sametime 7.5 development) allows for a much more flexible solutions that are less brittle and prone to breaking caused by API changes. An added benefit is the absence of compile time checks which means that you may develop and deploy components that doesn’t need to know of any other components that acts on the property changes it fire. The alternative to declarative events is the use of the Observer design pattern and Listener-interfaces en masse e.g. like in Swing.

Reading the articles has really got me thinking about how to leverage these capabilities in new and existing applications. I see great possibilities and the possibility of having many applications work together to form a greater whole.

I think the advent of composite applications will mean that the job of the application architect will become more challenging and you need to change the point of view from which applications are designed and developed. Applications will move from being monolithic entities to being composite and hence you need to decide on which properties to expose and how to work with “client” applications. This you need to decide on at design time. Applications should be designed and built as smaller interconnected components and not as the CD-ROM AutoInstall, 7-databases-in-one, applications of today.

Sounds intriguing but challenging…

All these possibilities are exciting and it will be interesting to see how many of the Lotus Expeditor capabilities will be exposed by the Notes 8 client and how many Notes 8 customers will pick up on it.