Building systems from off the shelf components

1. Building Systems from
Off-the-Shelf Components
Dr. Himanshu Hora
SRMS College of Engg. & Tech., Bareilly
INDIA

2. Building Systems from Off-the-Shelf
Components:
• Systems are being constructed with more and more
off-the-shelf components, for economic reasons and
because the expertise needed in many technical
areas is so specialized.
• Quality attributes can be maintained in a system,
even if that system is largely integrated from the-off-
shelf components whose design and interaction
mechanisms are not under the architecture.

3. Cont…
• The requirements process needs to be more flexible,
allowing what is available in the marketplace to
modify the requirements to provide a better overall
business solution.
• For systems built from off-the-shelf(OTS)
components, component selection involves a
discovery process, which seeks to identify assemblies
of compatible components,.
• Understand how they can achieve the desired quality
attributes, and deciding whether they can be
integrated the system being built.

4. Architectural Mismatch
• Not all components work together- even if they are
commercial products that claim compatibility.
• Components that were not developed specifically for
your system may not meet all of your requirement.
• Architectural mismatch usually shows up at system
integration time-the system will not compile, will not
link, or will not run.

5. Cont…
• What can you do about interface mismatch? Besides
changing your requirements so that yesterday’s bug
is today’s feature there are three things:
I. Avoid it by carefully specifying and inspecting the
components for your systems.
II. Detect those case you have not avoided by careful
qualification of the components.
III. Repair those cases you have detected by adapting
the components.

6. Techniques For Repairing Interface
Mismatch
• The alternative to changing the code of one or both
mismatched components is to insert code that
reconciles their interaction in a way that fixes the
mismatch.
• There are three classes of repair code:
I. Wrappers
II. Bridges
III. Mediators

7. Cont..
 Wrappers:
• The term wrapper implies a form of encapsulation.
• We can interpret interface translation as including:
• Translating an element of a component interface into
an alternative element.
• Hiding an element of a component interface.
• Preserving an element of a component’s base
interface without change.

8. Cont…
 Bridges:
• A bridge translates some requires assumptions of
one arbitrary component to some provides
assumptions of another.
• The key difference between a bridge and wrapper is
that the repair code constituting a bridge is
independent of any particular component.

9. Cont…
 Mediators:
• Mediators exhibit properties of both bridge and
wrappers.
• The major distinction between bridges and
mediators is that incorporate a planning function.

10. Techniques For Detecting Interface
Mismatch
• Discovering all of the requires assumptions of the
components for each of the services that will be
used by the system.
• Making sure that each requires assumption is
satisfied by some provides assumption in the system.

11. Techniques For Avoiding Interface
Mismatch
• One technique for avoiding interface mismatch is to
undertake, from the earliest phases of design a
disciplined approach to specifying as many
assumptions about a component’s interface as
feasible.
• Assumptions stated assertions about the sufficiency
of the services provided by each module and the
implement ability of each service by identifying
resources necessary to the module.

12. Model problem workflow
• An illustration of the model problem workflow is
shown in Figure. The process consists of the
following six steps that can be executed in sequence:
I. The architect and the engineers identify a design
question.
II. The architect and the engineers define the starting
evaluation criteria.

13. Cont…
III. The architect and the engineers define the
implementation constraints.
IV. The engineers produce a model solution situated in
the design context.
V. The engineers identify ending evaluation criteria.
VI. The architect performs an evaluation of the model
solution against the ending criteria.

15. Thank You
Dr. Himanshu Hora
SRMS College of Engg. & Tech., Bareilly
INDIA