Informatics 43 – May 28, 2015

Architectural Styles and Patterns

A named, commonly used set of

Components – subsets of functionality (we are concerned with what a component does, not how it is implemented) – aka modules

And Connections – function calls, shared memory, network traffic (message passing), sequencing, roles

Styles from last lecture

• Client – server

• Typically, the client and the server are separate computers that communicate over a network.

• Layered

• Typically, the modules in the various layers are all on one computer. Modules on one layer are implemented by calling functions from the layer below.

• Model View Controller

• Particularly useful for building flexible user interfaces.

3-tier architecture

3-tier architecture

3-tier architecture

n-tier architecture

Does Facebook only have one server?

Facebook has over 1 billion users!

Facebook has LOTS and LOTS of servers.

>180,000 servers across multiple data centers.

Non-Functional Requirements

Performance: Scalability: Availability: Security: Privacy: Reliability: Portability:

It's fast.

Uptime.

It's not privacy.

It's fast even with lots of users.

It's not security.

Don't delete my data by accident.

Works on different platforms(operating systems, web browsers, phones, etc.)

What do software architects do?

Figure out non-functional requirements Figure out what the components should be and

how they communicate. Instruct programmers Design tests Code (yes, software architects code)

But wait, there’s more

Pipes-and-filters

Unix command example

tr 'A-Z' 'a-z' <fnord.txt |

tr -cs 'a-z' '\n' | sort | uniq | comm -23 - /usr/share/dict/words

tr “translate” uppercase to lower case

tr turn everything except lowercase to newline

sort puts words in alphabetical order

uniq gets rid of duplicates

comm compares to words in dictionary and prints what’s not in the dictionary

But wait, there’s still more

Event driven

But wait, there’s more

Database-centric

“Where do they find the time?”

Clay Shirky: Cognitive Surplus

http://blip.tv/web2expo/web-2-0-expo-sf-2008-clay-shirky-862384