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(primitive, relation, tuple) event source can
be connected to any (primitive, relation, tuple)
event sink. It is easily possible to make se-
mantic connection errors, for example, match
a patient ID source with a clinician ID sink.
Moreover, errors can be made with respect
to the directionality of event connections,
for example, cycles. The presented semantic
approach is less error-prone with respect to
careless mistakes in composing WPC pages
since interfaces are semantically typed and
users do not have to deal with directional-
ity.
•
Premature commitment:
Do programmers
have to make decisions before they have the
information they need?
As argued earlier, the layout of WPCs on the
portal page has ramifications on the wiring
of the event connections and vice versa. This
dependency may, in some cases, force users
to prematurely commit to a specific interface
wiring or layout. This dependency is not pres-
ent in the semantic composition approach.
•
Progressive evaluation:
Can a partially
complete program be executed to obtain
feedback on “How am I doing?”
•
Hard mental operations:
Are there places
where the user needs to resort to fingers or
penciled annotation to keep track of what
is happening?
Hard mental operations may
be necessary only for very complex and large
portal pages that consist of many WPCs. In
this case, the user of the traditional system
may have to think deeply about how to con-
nect event connections and how to design
the event workflow. This operation is easier
in the newly proposed solution, since the CIM
provides an abstract representation of the
concepts relevant in the composed portal
page, and the user does not have to deal with
setting up event connections manually.
The traditional composition approach has
an advantage when it comes to progressive
evaluation. Portal pages can be executed at
any stage of the composition. This is also
true for the semantic approach, except for
cases where WPC components are deployed,
where the interfaces have not yet been
mapped to concepts in the PDO. (Of course,
it would be possible to simply ignore these
interfaces during portal execution.)
•
Role-expressiveness:
Can the reader see
how each component of a program relates
to the whole?
There is no significant dif-
ference between the two approaches with
respect to role-expressiveness.
•
Hidden dependencies:
Is every dependency
overtly indicated in both directions? Is the
indication perceptual or only symbolic?
•
Secondary notation:
Can programmers use
layout, color, or other cues to convey extra
meaning?
Choosing appropriate identifiers
for event interfaces and WPC components
can be used as an informal way to convey se-
mantics in the traditional approach. The same
is possible using the semantic composition
approach. Here, users do not deal with event
interfaces directly; however, their names are
exploited for deriving names of elements in
the CIM.
In the traditional approach, interface depen-
dencies among WPC components are hidden
from the user. The only way to make them
visible is by inspecting them one by one.
This is done by selecting a WPC on a browser
page and invoking the interface context menu
with the right mouse button. In the proposed
semantic approach to composition, concrete
interface dependencies are hidden in the same
way. However, users do not need to under-
stand them. It is sufficient to understand the
abstract (domain-oriented) dependencies in
the CIM, which are displayed as a graph.
•
Viscosity:
Resistance to change.
We con-
sider the following different categories of
changes: (1) change to the visual layout of
a portal page, (2) adding/removing WPCs
to/from a page, (3) change to a WPCs re-
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