Architectural Styles 2

CSSE 377 Software Architecture and Design 2Steve Chenoweth, Rose-Hulman InstituteWeek 2, Day 4, Thursday, Sep 16, 2011

Left – Model for the “repository” style of architecture is a warehouse. Half the battle is designing it so that the same lift truck can access anything you might need. The other half, perhaps, is knowing where that is! Fisheyeimage from www.moodleman.net/archives/202 .

2

Today HW 2 – Tim will post HW comments in Angel dropbox. More on arch styles – this

Bonus: a few examples of possible questions on the next biweekly quiz!

Project 2 – Time to work on Project 2 in class 11:55 PM – File a spreadsheet showing the “availability” of the

part of the system you stressed, and how much you predict you can improve it. Also turn in your journal with a discussion of that spreadsheet – how you decided on the numbers, especially.

3

Acknowledgements

Some of the material in these slides is taken from “An Introduction to Software Architecture” by Garlan and Shaw.

4

Arch styles, continuing…

Quick review of yesterday’s styles

New styles for today: Repository Interpreter Distributed Processes Domain Specific State Transition Systems

… and 1 more example

Garlan & Shaw’s TOC:

5

Call and Return

Main

One Two Three

Foo Bar

Review from Yesterday

6

Data Abstraction (Object Oriented)

Review from Yesterday

7

Implicit Invocation (Callback)

Event 1Event 2Event 3...

Foo

Bar

Register interest in events

Notification of events

Announcement of events

Example implicit invocation biweekly quiz question:

1. Why does “filters not knowing their neighbors” imply easy evolution?

Review from Yesterday

8

Pipe and Filter

Example pipe-and-filter biweekly quiz questions:

1. What does “often leads to batch processing” mean?2. Suppose this whole system ran in one computer, and passed

large images from filter to filter for processing. How would you modify its operation to save memory?

Review from Yesterday

9

LayeredUp

vC

Example layered system biweekly quiz question:

1. Suppose you discover that the “Useful system” level has to communicate directly with the “core level” to handle errors. What would you need to do to be sure doing this didn’t mess up your system design?

Review from Yesterday

10

Repositories (Database or Blackboard)

D C

New!

11

Repository Properties

Components: Central data structure Independent computational elements

Database: input stream selects processes Blackboard: State of central data structure selects

processes Used for finding nondeterministic solutions Has “knowledge base” vs DB at its center

Invariant: decisions are based on data on the shared blackboard

Today’s quiz – Q 1

Repositories

12

Repository Advantages/Disadvantages

Similar to Implicit Invocation style:Knowledge sources don’t know ID’s, butControl is driven by the blackboard

Context is important for reasoningUsually complex interpretation is the goal

Repositories

13

Repository – A Blackboard Example

Hearsay II (in Garlan & Shaw’s article)

Speech recognition Input stream – speech signal Blackboard – hypotheses about

what was being said Independent computing

elements – opportunistically tried to reach higher level conclusions – like “If these words say ‘Welcome to Terre Haute.” then that could be a coherent sentence.

Hearsay II’s blackboard architecture – from www.cs.cmu.edu/.../Soft_Arch/base.105.html .

Repositories

Additional uses for blackboards

Breaking complex cryptographic codes Sensory interpretation and analysis (such as computer

vision) Command and Control Systems Surveillance Systems Workflow Processing Case-based reasoning Symbolic learning Data Fusion

14

Repositories

15

Interpreter

Interpreters

16

Interpreter Properties Components:

Interpretation engine Memory containing pseudo-code Control state of interpretation engine Current state of program being simulated

Connectors: Closely bound, with direct procedure calls and shared state.

Interpreter examples – See PLC! Lisp and Scheme, etc.

Invariant? Details of the data manipulation are hidden by the high-level language.

Today’s quiz – Q 2

Interpreters

Interpreters – what you get

Binary instructions for a virtual machine, often called bytecode, as is done in Lua, Python, Ruby, Smalltalk, and many other systems (the approach was popularized in the 1970s by the UCSD P-system and UCSD Pascal)

A tree-like representation of the original program, such as an abstract-syntax tree, as is done for many prototype or educational interpreters

A tokenized representation of the source program, similar to Tcl

The characters of the source program, as was done in MINT and TRAC

17

Interpreters

18

Interpreter Advantages/ Disadvantages

Superb end-user programmability and maintainability; supports dynamically changing capabilities.

Slower than “raw code” doing the same thing.

Interpreters

Distributed Processes

SAP, as an example: Each server has a

“dispatcher” and a number of work processes These vary, depending on

resource needs E.g., one may have only

“dialog processes” and another may have just “background processing”.

19

Distributed Processes

20

Distributed Processes

Often described in terms of their topology: ring star

Sometimes described in terms of communication protocols: client/server peer-to-peer Heartbeat

Invariant? Physical isolation of functions goes with separation of responsibilities

Distributed Processes

21

Distributed ProcessesAdvantages/ Disadvantages Inherently flexible and reliable Can be slow instead of fast!

Use data close to its source, or batch it Keep “conversations” short

Maintenance of individual parts What happens when you change 1 interface?

Reliability Minimize the number of transactions

Distributed Processes

22

Distributed Process Example – Client/Server Like Web browser connected to a server… What are good & bad features of that?

PCClient

WebServers

PCClient

Hands outWeb pages

Each doing individual tasks

Gets requesteddata

DatabaseServers

A typical 4-tiered client-server systemClients “request services,” Servers “respond”.

ApplicationServers

Runs majorapplications

Distributed Processes

23

Distributed Process Example – Cloud (peer-to-peer)Issues – Achieving

scalability via distribution

Achieving availability via duplication

What’s “stateless vs stateful”

From “Building cloud-ready, multicore-friendly applications, Part 1: Design principles,” at http://www.javaworld.com/javaworld/jw-03-2009/jw-03-multicore-and-cloud-ready-1.html?page=4.

Today’s quiz – Q 3

Distributed Processes

Domain-Specific Styles

The prototypical example of a refined style – transaction processing using a credit / debit card:

24

Domain-Specific Arch

25

Domain-Specific Styles

Specific to a family of systems -- a product line

Some components are common, but may be implemented in different ways

Connections between common components are preserved across family

Domain-Specific Arch

26

Domain-Specific Example - Transaction processing systems

Used in banking, retail, loading docks, etc. Domain idea is that some activity of real value

occurs and needs to be recorded. Usually, assets change hands: You get money at a bank machine You buy an iTune for your iPod You checkout your groceries at Kroger’s 60 refrigerators get loaded onto your

store’s truck at the manufacturer’s warehouse

Image from www.handiramp.com/dock_equipment.htm .

Domain-Specific Arch

27

Domain-Specific Example - Transaction processing systems

What quality attributes are important? Performance – usually impacts productivity or customer

patience. Reliability – different meaning. Want all transactions to

be “atomic.”* Usually are distributed systems, with parts owned by

different organizations. Invariant: Guaranteed completion or roll-back of

transactions

* Famously, we want all the ACID properties in transactions: Atomicity, Consistency, Isolation and Durability. See, e.g., http://en.wikipedia.org/wiki/ACID.

Today’s quiz – Q 4

Domain-Specific Arch

28

Domain-Specific Example - Transaction processing systems

Example – Buying groceries at Kroger’s:

PIN Pad

POSRegister

Scanner

Kroger’sInventorysystem

In-storeprocessor

VISA

Recordstransaction

Scansgroceries

Gets VISAdata

Supplies item info to POS,Updates inventory system

POS = Point of Sale

Tracks item-levelsales

Authorizespayment

Store

Kroger image from compulsivec.wordpress.com/2007/03/ .

Domain-Specific Arch

State Transition Systems

Remember formal methods?

Here’s where a state diagram IS the design!

29

State-Transition Sys

30

State Transition Systems

Set of states as components Set of transitions between states, as

connectorsOften built on hardware “events”

Good style for reactive systems Invariant: The various “states” defined

determine what can be done there.

State-Transition Sys

31

State Transition System Example – Process Control

Use feedback or feedforward to control a process:

Diagram from http://en.wikipedia.org/wiki/Feedback. Feedback image from http://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-Computer-Science/6-302Feedback-SystemsFall2002/CourseHome/, an MIT open course on feedback systems

Today’s quiz – Q 5

State-Transition Sys

Examples

Again, taken from Garlan & Shaw’s Case Studies section.

33

Compiler – Pipe and Filter

A first try at compiler architecture – hand off the data from one step to the next, in “passes.”

34

Compiler – Modified Pipe and Filter

But the steps all use the common Symbol Table built during compilation, so need to have that large, shared area to update.

35

Compiler – Repository

And more improvements occur when the steps can interact, using rules to guide decisions … Like whether you are

trying to make a single block of object code out of one segment of source code.

Which leads to more of a repository style architecture.