System/Subsystem Design

System/Subsystem Design

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

Architectural Style

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

• components, e.g., client, server, DB
• connectors, e.g., procedure call, pipe, event broadcast
• 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

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 Example

Batch Sequential Architecture

Batch Sequential Architecture

• A 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 format or a new ordering so the next subsystem can work on the data
• The shared, specific file tightly couples the subsystems
• No real-time feedback, no concurrency

Batch Sequential Example

Batch Sequential Example

• Validate must complete and output before Sort
• Sort must complete and output before Update
• Update must complete and output before Report
• Each subsystem may have a different output format
• Each subsystem is developed based on the previous subsystem's output format
• No concurrency

Layered Architecture

Hierarchical decomposition of a system into subsystems (layers), with each providing a higher level of services provided from lower-level subsystems

• E.g., Presentation Layer
• E.g., Business Layer
• E.g., Data Layer

Closed Architecture: OSI Network Model

• closed architecture
• Each layer can only depend on the layer immediately below
• For data, it must flow from bottom to top, stopping at every layer

Open Architecture: Motif Library

• open architecture
• Each layer can access any layer below
• Functionality and can be accessed from any layer below

Repository Architecture

Repository Architecture

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

Repository: IDE

Model/View/Controller

Model/View/Controller

• Subsystems
• model subsystems are responsible for maintaining domain knowledge
• view subsystems are for displaying knowledge to the user
• controller subsystems 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

Client/Server Architecture

• Subsystems:
• Server provides one or more services to instances of clients
• 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

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.

Comparison

Virtual Machine Architecture

Virtual Machine Architecture

• Program Holds a program to execute in a particular language, probably a DSL
• Interpreter Knows how to decode the language instruction
• WorkingMemory Memory for the VirtualMachine
• VirtualMachine
  1. Fetch the instruction
  2. Fetch the data
  3. Execute the instruction
  4. Store the result in the WorkingMemory
  5. Update the Interpreter

Process Control Architecture

Process Control Architecture

• Controller gets feedback from a set of Sensors
• Controller performs actions on a set of Actuators

Event-Driven Architecture

Event-Driven Architecture

• Main EventLoop controls Subsystems
• Subsystem contains handlers
• EventLoop notifies Subsystems

Plug-In Architecture

• core system
• plug-in components
• Mix and match freely
• E.g., builtin vs. plug-in parsers

Observations

• Each of the architectures controls how you add subsystems to the system
• May define the output and input path
• May define characteristics of the output and input format
• Difficult to add a subsystem that does not fit the architecture
• Each type may be linked to a particular industry or application type