Common Architectural Styles & Patterns

Transcription

1 Common Architectural Styles & Patterns

2 some we ve already kind of discussed model view controller blackboard client/server layered pipe-and-filter

3 Lots of ways to classify all these Application Domain Knowledge deep shallow program design patterns architectural patterns styles domain specific architectures programming language application structures system structures

4 Today we ll check out: n-tiered architectures (n=1..?) mvc (a closer look, and a high level discussion of Ruby s use of this pattern) publish-subscribe (pub/sub) sense-compute-control

5 one-tier Architecture Sometimes used for single user applications! All components access files directly.! All components (UI, server) are on the same machine examples: MS Word, Excel, etc etc etc.

6 two-tier Architecture or client-server Client can t typically see database directly, meaning that the database is more secure. Allows multiple clients to access the database! Clients are often thick in that they do a lot of computation (except in the case of browsers in which case the server does a lot of the computation and responds to requests)! Application (middleware and display) layers are fused. example: network architectures.

7 three-tier Architecture Thinner clients: they only handle presentation (such as internet browser) Middle tiers can all run on their own server, offering more scalability of service good for: business applications where there is a data store behind a set of business logic rules, and where business logic is accessed by user interface components example: web service.

8 Model-View-Controller promotes separation of concerns: each component does its own job.! The Controller updates the model, which notifies the view to update The Controller may also ask for additional information about user input (such as the location on which the user clicked the mouse) TRIGGERS UPDATE REQUESTS INFORMATION! In some frameworks the controller and the view are merged (Java s Swing framework does this) because they are so closely interlocked.

9 MVC example: Ruby on Rails BROWSER HTTP request response CONTROLLER TRIGGERS UPDATE REQUESTS INFORMATION queries/ updates all display parameters sent html MODEL (database abstraction) VIEW (template)

10 Publish-Subscribe

11 Sense-Compute-Control Good for: embedded control applications and environmental feedback systems. or sensor-controller-actuator (picture courtesy of cicso) Sensor: reads information about the environment Controller: sends commands to the actuators like open flap, shut off heating Actuator: external devices dedicated to one job (display, thruster, heating element, wheel, wing) Operates on a loop tied to a clock. Loop through all sensors, run control functions, trigger all actuators. Heat Sensor Heat Sensor Heat Sensor if pollsensors.averageheat() > Controller.getTemp(): heaters.turnoff() if pollsensors.averageheat() < Controller.getTemp(): heaters.turnon() Heater Heater Heater

12 And So Many More! Structure Component-based Monolithic application aka "Big Ball of Mud" style Layered Pipes and filters Shared Memory Data-centric Blackboard Rule-based Messaging Event-driven aka Implicit invocation Publish-subscribe Asynchronous messaging Adaptable systems Plug-ins Microkernel Reflection Domain specific languages Distributed Systems Client-server (2-tier, 3-tier, n- tier exhibit this style) Shared nothing architecture Space based architecture Broker Peer-to-peer Representational State Transfer Service-oriented