Activation bar in UML Sequence Diagrams

A lot of folks get confused between the "life-line" concept and "activation bar" concept in Sequence Diagrams.

The vertical lines drawn are called the lifeline of the object. When the object is no longer alive, then we can draw an 'X' at the bottom of the line. So why do we need an activation bar? I have seen a lot of architects choosing not to draw the activation bar to keep the diagrams simple.

The activation bar (a.k.a focus of control) represents the time the object is "active", i.e. doing some processing, computing something, waiting for a response from a sub-routine, etc. So it is possible to model multiple interactions in a single diagram - for e.g. a lifeline can have nultiple activation bars.

Good whitepaper on WSRP Portlets

A friend of mine was confused on the concept of remote portlets and the WSRP protocol. I forwarded him this cool whitepaper that explains the concept of remote portlets in a simple and lucid language.

Some snippets from the whitepaper:

Remote portlets enable dynamic integration of business applications and information sources into portals.
This approach only works if all portlets are physically installed at the employee portal; the process of making new portlets available is tedious and expensive.
 
Instead of just providing raw data or single business functions that still require special rendering on the portal side, Web Services for Remote Portlets (WSRP) are presentation-oriented, interactive web services.
They are easy to aggregate and can be invoked through a common interface using generic portlet-independent code that is built into the portal. In addition, re-implementation of the presentation layer on each portal is avoided. The use of generic portlet proxies consuming all WSRP services conforming to the common interface eliminates the need to develop service-specific portlets to run on the portal.

The big difference between WSRP services and data-oriented web services is that they are presentation-oriented, interactive services that all have one common interface. This means that they simple plug into portal servers and do not require any service-specific code on the consuming portal.

Another point to consider is the comparison of remote portlets with mashups? Are they the same? Remote portlets and WSRP standards can be used to create mashups, but portlets also bring in the advantage of personalization and customization. Mashup's also need not just refer to aggregation of content. Wikipedia describes mashup as "A mashup is a website or Web 2.0 application that uses content from more than one source to create a completely new service. This is akin to transclusion." For e.g. tons of new applications built on top of Google Maps.