Architectural Design Lecture 11 Chapter 6

Architectural Design

• Architectural Design is the process of identifying the sub-systems making up a system and the framework for sub-system control and communication.
• It is an early stage of the system design process, representing the link between specification and design processes.
• It involves identifying major system components and their communications.

Architecture and System Characteristics

• Performance can be achieved by localizing critical operations and minimizing communications, using large rather than fine-grain components, and using a layered architecture with critical assets in the inner layers.
• Security can be achieved by localizing critical operations and minimizing communications.
• Safety can be achieved by localizing safety-critical features in a small number of sub-systems.
• Availability can be achieved by including redundant components and mechanisms for fault tolerance.
• Maintainability can be achieved by using fine-grain, replaceable components.

Architectural Conflicts

• Using large-grain components improves performance but reduces maintainability.
• Introducing redundant data improves availability but makes security more difficult.
• Localizing safety-related features usually means more communication so degraded performance.

Box and Line Diagrams

• They are very abstract and do not show the nature of component relationships nor the externally visible properties of the sub-systems.
• They are useful for communication with stakeholders and for project planning.

Architecture Reuse

• Systems in the same domain often have similar architectures that reflect domain concepts.
• Application product lines are built around a core architecture with variants that satisfy particular customer requirements.
• The architecture of a system may be designed around one or more architectural patterns or ‘styles’.

Layered Architecture

• It is used to model the interfacing of sub-systems.
• It organizes the system into a set of layers (or abstract machines) each of which provide a set of services.
• It supports the incremental development of sub-systems in different layers.
• When a layer interface changes, only the adjacent layer is affected.

Repository Architecture

• Sub-systems must exchange data, which can be done in two ways: shared data is held in a central database or repository and may be accessed by all sub-systems, or each sub-system maintains its own database and passes data explicitly to other sub-systems.
• When large amounts of data are to be shared, the repository model of sharing is most commonly used as it is an efficient data sharing mechanism.

Client-Server Architecture

• It is a distributed system model that shows how data and processing is distributed across a range of components.
• It can be implemented on a single computer.
• It consists of a set of stand-alone servers which provide specific services, and a set of clients which call on these services.
• It also consists of a network which allows clients to access servers.