System/Subsystem Design

System Decomposition

• subsystem provides a set of services to the system. A set of related operations that share a common purpose.
• subsystem interface set of services available to other systems.
• The Application Programmer Interface (API) includes the names of operations, parameters/types, and return types.
• System Design focuses on defining services

System/Subsystem Model

Architectural Style

An architectural style defines a family of systems in terms of a pattern of structural organization of components and connectors

• components, e.g., client, server, DB
• connectors e.g., procedure call, pipe, event broadcast
• Style consists of:
• vocabulary of components and connectors
• constraints on how they are combined

Common Architectural Styles

• Dataflow Systems: Pipe and Filter, Batch Sequential
• Virtual Machines: Rule-based Systems, Interpreters
• Repository: Databases, Hypertext Systems, Blackboards
• Independent Components: Peer-to-Peer, Client Server, Model/View/Controller, Event Driven
• Call and Return Systems: Main Program and Subroutines, Layered Systems, Object-Oriented Systems

Pipe and Filter Architecture

• Subsystems are called filters and associations between the filters are called pipes
• Filters only know the content and format of data being received and produced; nothing about the other filters in the system
• Filters execute concurrently with synchronization via pipes
• Very reconfigurable
• Transformational systems

Pipe and Filter Examples

Batch Sequential Architecture

• Small number of large stand-alone subsystems
• Must be executed in a fixed sequential ordering (batch)
• Typically work on large flat files, transforming the file into a new file format or changing the existing data so the next subsystem can work on the data
• The shared file causes the subsystems to be tightly coupled
• No real-time feedback, no concurrency

Batch Sequential Model

Layered Architecture

• AKA, n-tiered architecture
• Hierarchical decomposition of a system into subsystems (layers), with each providing a higher level of services implemented using lower-level subsystems

Closed Layered Architecture

• closed architecture each layer can only depend on the layer immediately below

Closed Layered Architecture

Open Layered Architecture

Open Layered Architecture

Layered Architecture Analysis

Repository Architecture

• Subsystems are independent and interact with a central repository
• Examples: Payroll or banking system, Modern IDE/Compiler, Blackboard

Repository: IDE

Model/View/Controller

• Subsystem: model responsible for maintaining domain knowledge
• Subsystem: view displaying knowledge to the user
• Subsystem: controller manage the interactions with the user
• Model subsystems do not depend on view or controllers.
• Changes in model state propagate via a subscribe-notify protocol
• Examples: File system, database

Client/Server Architecture

• Subsystem: Server provides one or more services to instances of clients
• Subsystem: Clients ask for services, and clients interact with users
• An information system with a central DB is an example
• Web servers (multiple servers)

Peer-to-Peer Architecture

• Generalization of client/server: clients can be servers and vice versa
• The control flow of each subsystem is independent of others except for the synchronization of requests.

Virtual Machine Architecture

Process Control Architecture

Event-Driven Architecture

Event-Driven Architecture: Mediator Topology

Event-Driven Architecture: Mediator Topology

Event-Driven Architecture: Broker Topology

Event-Driven Architecture Analysis

Microkernel Architecture

• AKA, Plug-In
• Component: Core system
• Component: plug-in modules

Microkernel Architecture

Microkernel Architecture Analysis