Conducting Component Level Design

Conducting Component Level Design

• Introduction
• Component-level design is elaborative in nature.
• It transforms information from requirements and architectural models into a design representation that provides sufficient detail to guide the construction (coding and testing) activity. 
• The following steps represent a typical task set for component-level design, when it is applied for an object-oriented system. 
•  Step 1. Identify all design classes that correspond to the problem domain.
• Using the requirements and architectural model, each analysis class and architectural component is elaborated… 
• Step 2. Identify all design classes that correspond to the infrastructure domain. 
• These classes are not described in the requirements model and are often missing from the architecture model, but they must be described at this point. 
• Classes and components in this category include
• GUI components (often available as reusable components), 
• Operating system components, 
• Object and data management components
• Step 3. Elaborate all design classes that are not acquired (Obtain) as reusable components.
• Elaboration requires that all interfaces, attributes, and operations necessary to implement the class be described in detail. 
• Design heuristics (e.g., component cohesion and coupling).
• Step 3 (a) . Specify message details when classes or components collaborate. 
• The requirements model makes use of a collaboration diagram to show how analysis classes collaborate with one another. 
• Step 3 (b). Identify appropriate interfaces for each component.
• Within the context of component-level design, a UML interface is “a group of externally visible (i.e., public) operations.
• The interface contains no internal structure, it has no attributes, no associations . . .
• Step 3 (c). Elaborate attributes and define data types and data structures required to implement them.
• In general, data structures and types used to define attributes are defined within the context of the programming language that is to be used for implementation. 
• UML defines an attribute’s data type using the following syntax: 
• name : type-expression initial-value {property string} 
• where name is the attribute name, type expression is the data type, initial value is the value that the attribute takes when an object is created, and property-string defines a property or characteristic of the attribute. 
• Step 3 (d). Describe processing flow within each operation in detail.
• This may be accomplished using a programming language-based pseudocode or with a UML activity diagram. 
• Each software component is elaborated through a number of iterations that apply the stepwise refinement concept .
• Step 4. Describe persistent data sources (databases and files) and identify the classes required to manage them.
• Databases and files normally transcend the design description of an individual component. In most cases, these persistent data stores are initially specified as part of architectural design. 
• Step 5. Develop and elaborate behavioral representations for a class or component. 
• UML state diagrams were used as part of the requirements model to represent the externally observable behavior of the system. 
• Step 6. Elaborate deployment diagrams to provide additional implementation detail. Deployment diagrams are used as part of architectural. 
• Step 7. Refactor every component-level design representation and always consider alternatives.