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System Design
Lecture 28
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Overview
n System Design n System Architecture n Model-View-Controller n Distributed Systems n Design Standards
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System Design
n System design focuses on the overall structure of the system (i.e., system architecture) n Decisions made during the system design inform the rest of the design process. n We need to consider the impact of the selected technology on the future implementation of a given design. n All design activities need to be prioritized and tradeoffs identified
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System Architecture
n A major part of system design is defining the system architecture n No general consensus on the definition of system architecture n The architecture of a system is concerned with n its overall structure n the relationships among its major components, and n their interactions n The structure and interactions of human, hardware and software elements of the system are considered
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System Design Activities
n System design activities:
n Sub-systems and major component identification n Identifying concurrency n CPU allocation for sub-systems n Selection of data management strategies n Setting standards for HCI and code development n Planning control aspects of the application n Planning tests n Prioritizing design trade-offs n Determining deliverables
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Software Architecture
n Like system architecture, no general consensus on the definition of software architecture n The architecture of a system is its class structure. Part of the architecture is the way in which classes are grouped together. (Booch, 1994) n A description of the subsystems and components of a software system and the relationships between them. (Buschmann, 1996) n Other descriptions as well.
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Dividing Systems into sub-
systems
n There are two general approaches to dividing
systems into sub-systems:
n Layering n Partitioning
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Layering
n Layering: sub-systems represent different levels of abstraction n In a closed architecture messages can be sent to adjacent layers only n In an open architecture messages can be sent to any lower layer
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Partitioning
n Partitioning: sub-systems represent separate functions n Some layers may have to be partitioned to reduce their complexity n Partitioning is done during analysis, but refined at the design stage n Typically a system architecture involves both layering and partitioning
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Example of Sub-systems
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Model-View-Controller
n Many object-oriented systems are structured according to Model-View-Controller architecture. n Model represents the system's main functionality. n View allows presentation of data to the user. n Controller manages updates to the views. n MVC allows separation of data processing from its presentation to the user. n MVC allows displaying the information to different users in different way. n MVC also facilitates the consistency between different views.
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MVC—An Example
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