Semantic Composition of Web Portal Components - End User Computing Challenges and Technologies: Emerging Tools and Applications - page 171

basis for our approach. While there are several
technical development guides on how to imple-
ment WPCs for specific portal server platforms,
there has been little systematic treatment of the
common conceptual aspects of WPC models. In our
research, we have concentrated on studying WPC
component technologies that support event-based
communication among components. In particular,
we have concentrated on three specific technologies
(Microsoft's WebParts, IBM's Portlets, and DNN's
Modules).
All three platforms support event-based com-
munication; however they vary with respect to
technical details. To date, Microsoft's WebPart
technology is arguably the most advanced, in that
WebParts can exchange events on the client side
in addition to the server-side events provided by
all WPC models. The advantage of using client-side
event communication is that it does not require a
“post-back” operation involving the server, which

often causes undesired time delays during user
interaction. Furthermore, WPC platforms differ
with regard to the degree with which the data
types of event payload are predefined. Microsoft's
WebPart platform defines three standard data types
for event payload, namely primitive values (cells),
tuples of values (rows), and ordered relations
(lists). The conceptual composition model shown
in Figure 2 most closely reflects this WebPart
platform. Still, it can also be realised based on the
other WPC platforms mentioned in this section.
However, these other platforms leave the definition
of data types for event-based information exchange
up to the portal developer.
The composition model in Figure 2 shows
possible types of connections between outgoing
event interfaces (event sources) and incoming
interfaces (event sinks) belonging to different WPC
components. Connections between event sources
and sinks of the same physical data type are called

Figure 2. Composition model for Web portal components

1

Relation Source

-labels[1..*]

*

1

Tuple Source

-labels[1..*]

1

1

Primitive Source

-label

Event Source

* *

WPC Event Interface

Direct Primitive Con

*

-name
-isClientBased : bool

*

Projected Connection

Direct Tuple Connection

* *

*

Event Sink Selected Connection

Direct Relation Con

*

*

*

1

1

Primitive Sink

Direct Connection

Mediated Connection

-label

1

Tuple Sink

-labels[1..*]

*

1

Relation Sink

-labels[1..*]

Connection