Information Technology Reference
In-Depth Information
requirements, reducing multiplicities in associations to speed up queries, rear-
ranging execution order, and adding derived attributes to improve the access time
to objects.
Object design is not sequential. The activities described occur concurrently.
Interface specifications and reuse activities occur first, yielding an object design
model that is then checked against the use cases. Restructuring and optimization
activities occur next, once the object design model for subsystem is relatively
stable. Focusing on interfaces, components and design patterns result in an object
design model that is easier to modify.
8.1.2 Activities in OOD
During object design our understanding of each object deepens. As the focus of
system design was on identifying large chunks of work that could be assigned to
individual teams or developers, the focus of object design is to specify the
boundary between objects. At this stage a large number of developers refine and
change many objects and their interfaces. Interface specification activities of
object design include (Bruegge and Dutiot
2004
):
• Identifying missing attributes and operations
• Specifying type signatures and visibility
• Specifying invariants
• Specifying preconditions and postconditions
During system development we would have made decisions about the system
and produced several models:
• The analysis object model describing the entity, boundary and control objects
that are visible to user. The analysis object model includes attributes and
operations for each object.
• Subsystem decomposition describes how these objects are partitioned into
cohesive pieces that are realized by different teams of developers. Each
subsystem
includes
high-level
service
descriptions
that
indicate
which
functionality it provides to others.
• Hardware/Software mapping identifies the components that make up the
virtual machine on which we build solution objects. This may include classes
and APIs defined by existing components.
• Boundary use cases describe, from the user's point of view, administrative
and exceptional cases that the system handles.
• Design patterns selected during object design reuse describe partial object
design models addressing specific design issues.
All these models however reflect partial view of the system. The goal of the
object design is to produce the object design model that integrates all of the above
