Week 5 Flashcards
COTS systems?
Commercial Off-The-Shelf systems.
Design processes and system models?
Structured design processes involve developing a number of different system models.
They require a lot of effort for development and maintenance of these models and, for small systems, this may not be cost-effective.
However, for large systems developed by different groups, design models are an important communication mechanism.
Common activities in OOD processes?
- Define the context and modes of use of the system;
- Design the system architecture;
- Identify the principal system objects (real-world entities or concepts that serve as building blocks of the design).
- Develop design models;
- Specify object interfaces.
System context and interactions?
Understanding the relationships between the software that is being designed and its external environment is essential for deciding how to provide the required system functionality.
Understanding of the context lets you establish boundaries which helps you decide what features are implemented in the system.
Context and interaction models?
A system context is a structural model that demonstrates the other systems in the environment of the system being developed.
An interaction model is a dynamic model that shows how the system interacts with its environment as it is used.
Object class identification?
User grammatical approach based on a natural language description of the system.
Base the identification on tangible things in the application domain.
Use a scenario-based analysis.
Some knowledge source to discover objects, attributes and operations.
State diagrams?
Used to show how objects or sub systems respond to different messages and events and how the object instances change state.
State diagrams are useful high-level models of a system or an object’s run-time behaviour.
You don’t usually need a state diagram for all of the objects in the system (state model adds unnecessary detail to simple designs).
Interface specification?
Object interface defines set of ways to interact with an object.
An important part of any design process is the specification of the interfaces between the components.
Object interfaces have to be specified so that the objects and other components can be designed in parallel.
Objects may have several interfaces.
Design patterns?
A design pattern is a way of reusing abstract knowledge about a problem and its solution.
A pattern is a description of the problem and the essence of its solution.
It should be sufficiently abstract to be reused in different settings.
Pattern descriptions usually make use of object-oriented characteristics such as inheritance.
Pattern elements?
- Name
- Problem description
- Solution description (template for a design solution if not a concrete one).
- Consequences (results and trade-offs of applying the pattern).
Observer pattern?
Name (observer).
Description (separates display of object state itself and allows alternative displays to be provided).
Problem description (used when multiple displays of state are needed. Not necessary for the object that maintains the state information to know about the specific display formats used).
Solution description.
Consequences (optimisations to enhance display performance are impractical).
