Semantic Composition of Web Portal Components - End User Computing Challenges and Technologies: Emerging Tools and Applications - page 183

alisation without impacting its interface,
(4) change to a WPCs realisation impacting
its interface, and (5) change to the end-user
problem domain. In our approach, a change
to the visual layout (Change category 1) does
not have any impact on the functioning of the
portal. In contrast, a visual layout change in
the traditional approach may require further
changes to event interface connections. The
reason for this is the directionality of interface
connections in the traditional approach. Users
(in Western cultures) often fill out forms in
an order influenced by their visual layout
(top to bottom, left to right). Event sinks and
sources should be connected in this direc-
tion to be able to propagate data between the
WPCs that make up the form. If their visual
arrangement is changed, the direction of
these event connections should be changed
to avoid counter-intuitive behaviour. This is
not necessary in our approach, which has a
lower viscosity to this category of change.
A similar consideration is made for the
second category of change (adding/deleting
WPCs to/from portal pages). When a WPC
is removed from a page using the traditional
approach, its removal may cause a gap in a
transitive event data propagation scheme,
requiring changes to source/sink interface
connections of the remaining WPCs. More-
over, adding a new WPC component to a
page may change the page's layout causing
further changes as described in category 1.
Both effects are not present in our approach,
leasing to lower viscosity in this category.
Changes according to category 3 are fully
encapsulated and the viscosity of both ap-
proaches is identical. Changes according to
category 4 can be in one of four subcatego-
ries: (a) technical retyping of interfaces (e.g.,
the change from a primitive event interface
to a tuple event interface); (b) adding event
interfaces mapped to concepts existing in the
PDO; (c) adding event interfaces mapped to

new concepts in the PDO; and (d) deleting
event interfaces. The first subcategory of
change requires end users to redefine interface
connections in the traditional approach. This
is not necessary in our approach, since end
users deal with connections on a higher level
of abstraction (domain concepts). The second
subcategory of changes requires a change in
the CIM only in those cases where the new
WPC interface refers to a PDO concept not
yet instantiated in the CIM. In the traditional
approach, it always requires changes to in-
terface connections. The third subcategory of
changes (c) requires an extension of the PDO
and the CIM in our approach vs. the definition
of new interface connections in the traditional
approach. The final subcategory of changes
(d) requires changes only in the traditional
approach according to the argument made for
change category 1. In summary, the viscosity
of the semantic approach to composition is
lower than the traditional approach except
for subcategory (c), in which case it may be
higher, depending on the severity of the PDO
update. Still, such updates should be rare.

• Visibility and Juxtaposability: Ability to

view components easily respectively to place
any two components side by side. Both the
traditional approach and the semantic ap-
proach proposed in this chapter can visualise
the graphical positioning of WPCs that reside
on the same portal page. However, their
event connections can only be visualised
one connection at a time using a context
menu invoked with the right mouse button.
In addition to this, to semantic approach of-
fers a graphical visualisation of the CIM that
governs the wiring of any given portal page,
resulting in a higher overall visibility.

In summary, the semantic composition ap-
proach described in this chapter has benefits in all
but one cognitive dimension, namely progressive
evaluation. This deficit can be compensated by al-