University:
California State University, Northridge
Course:
COMP 684 | Software Architecture and Design
Academic year:

2024
Views:

92

Pages:

17
Author:

Sanaa Tate

Style – Object-Oriented Systems: Components & Connectors  Components: Classes & Objects  Connectors: Method calls Object-Oriented Systems: Key Characteristics  Call and return architecture  Interaction through method invocation  Based on data abstraction:   Encapsulation Information hiding Object-Oriented Systems: Encapsulation  A packaging / scoping mechanism for names   Names can refer to data, types, … Especially, a means of packaging data Access points at interface Data Object-Oriented Systems: Information Hiding  Design principle  A module    has a “secret”, usually a design decision makes particular design choice “invisible” to clients E.g.  Choice of algorithm  Data structure Object-Oriented Systems: Strengths  Naturally supports information hiding, which shields implementation changes from clients  Encapsulation and information hiding reduce coupling => Enhances maintainability  Allows systems to be modeled as collections of collaborating objects => can be an effective means of managing system complexity Object-Oriented Systems: Weaknesses  Object identity must be known for method invocation => Identity change of an object affects all calling objects  Contrast this to pipe-and-filter …  Concurrency problems through concurrent access Object-Oriented Systems: Variations  Active classes  When instantiated, control their own execution  Can operate standalone (rather than being invoked by other classes)  Own thread  Other OO variants such as support (or not) of multiple inheritance, interfaces, static typing, etc. Object-Oriented Systems: Examples Object-Oriented Systems: Examples  Object-oriented systems can be seen as an evolution of ADTs Style: Hierarchically Layered Systems  3-Tiered Enterprise Applications Presentation Domain Logic Technical Services Hierarchically Layered Systems: Components & Connectors  Components: Layers  Connectors: Protocols that define how layers interact Hierarchically Layered Systems: Key Characteristics  Hierarchical organization     Only adjacent layers communicate Each layer provides services to the level above and serves as a client to the layer below Lower layer is unaware of higher layer Each layer hides its lower layers from the layers above Hierarchically Layered Systems: Strengths  A single layer acts as a coherent whole  No need to know much about other layers  Portability:  Easy to replace a layer with another implementation of its services  Maintainability: Each layer’s role is well defined  Minimized dependencies  Supports design based on increasing levels of abstraction Hierarchically Layered Systems: Weaknesses  Performance  High-level functions only indirectly access low-level functions -> must go through the various layers  Difficult to find the right abstractions (especially with many layers involved)  Risk of abstracting the wrong thing  Not all systems fit into the layered style  The scope of one component may overlap several layers Hierarchically Layered Systems: Variations  Layer may accesses other lower level layers than just the layer below   Less pure Increased performance Hierarchically Layered Systems: Examples Hierarchically Layered Systems: Examples  Protocols  TCP/IP  OSI ISO model  X Window system  Enterprise Applications  Presentation layer  Domain logic layer  Data source layer