Architectural Patterns (Styles), Frameworks, and Tactics

Week 3

M. Ali Babar

Practicalitiesact ca t es

Guidelines for assignments released

First set of assignments (individuals and group) g ( g p)released

Start working on them and ask questions if not sure

Everyone in a group by now?

Today, we will have the first group paper presentation in the exercise class actively participate!!!

Lecture Outlineectu e Out e

Software patterns and their origin

Architectural patterns and styles what is the p ydifference?

Some common architectural patterns and their benefits, drawbacks, and usage

Frameworks and their usage in architectural design

Architectural Tactics and their relations with patterns

Software PatternsSo t a e atte s

What is a pattern? A pattern is a solution to a problem A pattern is an abstraction from a concrete form which keeps

recurring in specific non arbitrary contextsrecurring in specific non-arbitrary contexts

From "Understanding and Using Patterns in Software Development" Dirk Riehle and Heinz ZullighovenDevelopment , Dirk Riehle and Heinz Zullighoven Patterns are ways to describe best practices, good design,

and capture experience in a way that it is possible for others hi ito reuse this experience

The goal of patterns is to create a body of literature to help software developers resolve recurring problems encountered p g pthroughout the software development.

Driving Patterns from Core Solutionsg atte s o Co e So ut o s

Patterns is about core solutions different singular solutions which look completely different on

the surface, yet have a deeper similarity intellectual challenges of patterns is finding and isolating this intellectual challenges of patterns is finding and isolating this

core amongst all the surrounding stuff that's needed on real projects

Patterns should have recurrence Tried and tested

h l i b li bl i l f diff i i the solution must be applicable in lots of different situations A well-known pattern is in the vocabulary of the profession

Pattern Originsatte O g s

Software patterns first became popular with the work published in the book Design Patterns: Elements ofpublished in the book Design Patterns: Elements of Reusable Object-Oriented Software by GoF

Pattern-Oriented Software Architecture: A System of yPatterns (also called the POSA book) A system of patterns Patterns for concurrent and networked objectsatte s o co cu e t a d et o ed objects Patterns for resource management

Patterns of Enterprise Software Architecture Technology specific patterns e g J2EE core patterns Technology specific patterns, e.g. J2EE core patterns,

Microsoft patterns, integration patterns Patterns for Domain Specific Applications

E b dd d li ti ft d t li fi i l Embedded applications, software product line, financial applications

Pattern Documentationatte ocu e tat o

A pattern language is a structured method of d ibi d d i i i hi i ldescribing good design practices within a particular domain (from Wikipedia) Noticing and naming the common problems in a fieldNoticing and naming the common problems in a field Describing the key characteristics of effective solutions for

meeting some stated goalHelping the designer move from problem to solution in a Helping the designer move from problem to solution in a logical way and

Allowing for many different paths through the design process The documentation for a design pattern contains

problem that the pattern addresses, the context in which the pattern is used the suggested solution additional sections topattern is used, the suggested solution additional sections to provide more information, e.g. the strength and weakness of the pattern

Patterns provide a good way of documenting design Patterns provide a good way of documenting design

Pattern Description in Pattern Repositoryatte esc pt o atte epos to y

Observer patternObserver pattern

Using Patterns for Quality AttributesUs g atte s o Qua ty tt butes

Single Sign On (SSO) is a typical scenario for biliusability

SSO components observer changes to the session state Using Observer Design Pattern to implement SSO Using Observer Design Pattern to implement SSO

Tomcats solution: Session defines a Session creation and Session destruction

events Single Sign On Valve component registers a

SessionListener interface with the Session Session is the Subject and SingleSignOn is an Observer When the session is destroyed, this session event listener is

called back The Single Sign on component can decide tocalled back. The Single Sign on component can decide to log off the user from its web application

Tool Supportoo Suppo t

Software Architecture StyleSo t a e c tectu e Sty e

Architectural style is a way of classifying architecture largely by morphological characteristics - in terms of form, techniques, materials, etc. However it is not a h li ti f d t di hit t l kholistic way of understanding architectural works because of its emphasis on style. from Wikipediafrom Wikipedia

Software Architecture StyleSo t a e c tectu e Sty e

Software architectural style (also called architectural pattern) refers to a set of design rules that identify the kinds of components and connectors that may be

d t t b t t thused to compose a system or subsystem, together with local or global constraints on the way the composition is donecomposition is done M. Shaw and P. Clements

Patterns vs. Architecture Stylesatte s s c tectu e Sty es

GoF design patterns describe the implementation of micro architecturesmicro architectures small-scale object interactions

Architecture styles are high level structure for y gsoftware systems concerned with the construction context of a whole system,

rather than just some part of a systemj p y understanding of software architecture styles allows an

engineer to make principled choices among design alternatives

An architectural system representation is often essential to the analysis and description of the high level properties of a complex system

Ad ti f tt hit t t l d d Adoption of patterns vs. architecture styles depends on an architects point of view and the scale of a system

Some Architecture Patterns (Styles)So e c tectu e atte s (Sty es)

Layered Systems Pipes and Filters Model View Control Data Abstraction Blackboard

E t b d I li it I ti Event-based, Implicit Invocation Repositories Other Familiar Architectures Other Familiar Architectures

Distributed processes: client-server Domain specific architecture: software product line

Layered Systems (1/2)aye ed Syste s ( / )

Context A large system requires decomposition A layered system is organized hierarchically, each layer

providing service to the layer above it and serving as a clientproviding service to the layer above it and serving as a client to the layer below.

Layers is an architectural style that structures applications so they can be decomposed into groups of subtasks

BenefitsD i b d i i l l f b i Design based on increasing levels of abstraction

Modularity and encapsulation ReusabilityReusability Maintainability, changes to the function of one layer affect at

most two other layers

Layered Systems (2/2)aye ed Syste s ( / )

Drawbacks A layering violation leads to changes to one layer resulting

in changes to every other layer, which is an expensive and error prone propositionerror prone proposition

Layering can incur overhead of performance.

Known uses J2EE, .Net MySQL Hibernate Multi-tier internet-based applications TCP/IP network protocol implementation TCP/IP network protocol implementation X Window System protocols

Layered J2EE Architectureaye ed J c tectu e

http://www.javaworld.com/javaworld/jw-06-2002/jw-0628-j2eevsnet_p.html

Layered .Net Architectureaye ed et c tectu e

http://www.javaworld.com/javaworld/jw-06-2002/jw-0628-j2eevsnet_p.html

Pipeline and Filters (1/4)pe e a d te s ( / )

Context programs that process streams of data each component has a set of inputs and a set of outputs.

The filters are components that processing inputs of The filters are components that processing inputs of the pipeline A filter may enrich, refine, or transform its input data

The pipes are the connectors between a data source and the first filter, between filters,

and between the last filter and a data sinkand between the last filter and a data sink

Pipeline and Filters (2/4)pe e a d te s ( / )

Implementation tips Divide the functionality of the problem into a sequence of

processing steps Define the type and format of the data to be passed along Define the type and format of the data to be passed along

each pipe Determine how to implement each pipe connection. Design and implement the filters Design for robust handling of errors

Pipeline and Filters (3/4)pe e a d te s (3/ )

Benefits Simplifies the composition of the behaviors of the individual

filters through data streams as inputs and outputs Reusability: any two filters can be hooked together, provided y y g , p

they agree on the data that is being transmitted between them

Maintainability: new filters can be added to existing systemsMaintainability: new filters can be added to existing systems and old filters can be replaced by improved ones

Concurrency: Each filter can be implemented as a separate task and potentially executed in parallel with other filterstask and potentially executed in parallel with other filters

Pipeline and Filters (4/4)pe e a d te s ( / )

Drawbacks pipe and filter systems are typically not good at handling

interactive applications have to maintain correspondences between two separate have to maintain correspondences between two separate,

but related streams added work for each filter to parse and unparse its data

Known uses Unix shell Tomcat, JBoss, Axis, Axis2 request handler/interceptor ASP.Net Language parser Language parser MySQL query processor

Architecture Styles in JBossc tectu e Sty es J oss

Invocations are processed in Pipeline and Filter style

htt // d / li /jb /jB hthttp://www.cse.unsw.edu.au/~yliu/jboss/jBoss.htm

Model View Controller (MVC)ode e Co t o e ( C)

What is Framework?at s a e o

A software framework is a reusable design for a f ( b )software system (or subsystem)

a reusable, semi-complete application that can be specialized to produce custom applications.p p pp

Frameworks are larger modeling constructs than architectural patterns they are used to model the entire application or a subsystem

of the application a mature framework contains recurring design structures that

demonstrates properties e.g. extensibility, decoupling, and elegance

A software framework can support alternativeA software framework can support alternative architecture patterns to solve the same problem

Example Frameworksa p e a e o s

Apache Struts is an open-source framework for developing J2EE web applicationsdeveloping J2EE web applications.

Hibernate is an Object-relational mapping (ORM) solution for the Java language.g g

JavaServer Faces (JSF) is a Java-based Web application framework that simplifies the development of user interfaces for J2EE applicationsof user interfaces for J2EE applications.

Eclipse is a free software / open source platform -independent software framework for delivering IDE environmentenvironment

Java Native Interface (JNI) allows Java code running in the Java virtual machine (VM) to call and be called by native applications and libraries written in other languages, such as C, C++ and assembly.

Eclipse Plug-in Architecturec pse ug c tectu e

A plug-in in Eclipse is a component that provides a certain type of service within the context of the Eclipsecertain type of service within the context of the Eclipse workbench

Architectural Tacticsc tectu a act cs

Achievement of quality attributes relies on decisions called tactics; Styles or pattern applies tacticscalled tactics; Styles or pattern applies tactics

For example, redundancy, that influences a qualityFor example, redundancy, that influences a quality attribute

D i i t f ll ti f d i i d Design consists of a collection of decisions and a collection of tactics is called an architectural strategy

Tactics may also be composed of other tactics, e.g., redundancy = data or computation redundancy

Patterns package tactics: a pattern that support availability is likely using both redundancy and y y g ysynchronization tactics.

Ensuring Availabilitysu g a ab ty

A failure occurs when a system cannot deliver a service that is expected of that systemservice that is expected of that system.

A failure is an observable property of a systemsA failure is an observable property of a system s state.

A f lt i t f t h t ti l t A fault in any part of a system has a potential to cause a failure; a system can be repaired or recovered from a failure.

Approaches to ensuring availability may be: Fault detection Fault detection Fault recovery Fault prevention

Availability Tacticsa ab ty act cs

Fault Detectionau t etect o

Ping/Echo One component issues a ping and expects an echo from

another component within a predefined time

Heartbeat (dead man timer) One component emits a heartbeat message (can also carry

data) periodically and another component listens for it If the heartbeat fails, the originating component is assumed

to have failed and a fault correction component is notifiedp

Exception One method for recognising faults is to encounter an

exception. The exception handler typically executes in the same p yp y

process that introduces the exception

Recovery Preparation and Repaireco e y epa at o a d epa

VotingP i d d t d i l Processes running on redundant processors send a simple value to voter who decides about the deviant behavior

Active redundancy All redundant components respond to events in parallel all

back ups are current switching time is the recovery timep g y

Passive redundancyO t d t t d i f th th One component responds to events and informs the others of state updates to be made backup may not be updated

Spare A standby spare computing platform is configured to replace

many different failed componentsy p

Recovery - Reintroductioneco e y e t oduct o

Shadow operation A previously failed component may be run in shadow mode

for a short time to make sure that it mimics the behaviour of the working components before restoring it to servicethe working components before restoring it to service

State resynchronisationState resynchronisation The passive and active redundancy tactics require the

component being restored to have its state upgraded before its return to service

Ch k i t/ llb k Checkpoint/ rollback A checkpoint is recording of a consistent state created either

periodically or in response to specific eventsperiodically or in response to specific events

Fault Preventionau t e e t o

Removal from service This tactic removes a component of the system from

operation to undergo some activities to prevent anticipated failurefailure

TransactionTransaction A transaction is the bundling of several sequential steps

such that the entire bundle can be undone at once

Process monitor Once a fault in a process has been detected, a monitoring

process can detect the non-performing process and create a new instance of it, initialised to some appropriate state as innew instance of it, initialised to some appropriate state as in the spare tactic

Modifiability Tacticsod ab ty act cs

Localize Changeoca e C a ge

Maintain semantic coherenceR f t l ti hi ibiliti i d l Refers to relationships among responsibilities in a module

Anticipate expected changesAnticipate expected changes Considering a set of possible future changes helps

G li th d l Generalize the module Adjusting the input rather than the module

Limit possible options Reduced options will reduce the effect of these modifications

Abstract common services

Prevent Ripple Effectse e t pp e ects

Hide informationD idi b t th bli & i t i f ti Deciding about the public & private information

Maintain existing interfacesMaintain existing interfaces Adding interfaces, adding adapter, providing stubs

R t i t i ti th Restrict communication paths Reduce the number of modules that consumes data

produced by a given modules, and reduce the number of d t d i d ldata producing modules

Use an intermediaryUse an intermediary

Defer Binding Timee e d g e

Runtime registrationS t l d l P bli h/ b ib i t ti Support plug-and-play or Publish/subscribe registration

Configuration filesConfiguration files Intended to set parameter at start up

P l hi Polymorphism Allow late binding of the method calls

Component replacement Allow load time binding

Adherence to defined protocols Allow runtime binding of independent processesAllow runtime binding of independent processes

Performance Tacticse o a ce act cs

Resource Demandesou ce e a d

Increase computation efficiency Improving algorithms to decrease latency

Reduce computational overhead Remove intermediaries Java classes instead of RMI

Manage event rate Reduce sampling frequency for monitoring events

Control frequency of sampling Lower frequency of requesting samples, loss of requests

Resource Managementesou ce a age e t

Introduce concurrency Concurrency can reduce blocked time for processes

Maintain multiple copies Computations transfer computation to clients, which are

replicas of the comp tationreplicas of the computation Data Caching data: System is responsible for

synchronization of datay

Increase available resources Faster or additional processors Additional memory Faster networks

Resource Arbitrationesou ce b t at o

Scheduling processes, buffers, and networks First-in/First-out or Fixed-priority scheduling

Dynamic priority scheduling Round robin: Orders the requests and then assigns

reso rces to the ne t req est in the orderresources to the next request in the order Earliest deadline first

Static scheduling

Architectural Patterns and Tacticsc tectu a atte s a d act cs

SummarySu a y

We know what are software patterns and their origin

Architectural patterns and styles had different p ydefinitions but lost the distinctions

Layered, Pipe & Filter, MVC architectural patterns

Frameworks can be leveraged for rapidly building complex and large applications

Architectural tactics are design decisions

Referencese e e ces

Chapter 5 of book by Bass, L., et al.

Selected material on three architectural patterns from book by Buschman, F., et al.Buschman, F., et al.

Design Patterns (From Wikipedia)htt // iki di / iki/D i tt %28 t i %2 http://en.wikipedia.org/wiki/Design_pattern_%28computer_scien%29

C 2 Core J2EE Design Pattern http://java.sun.com/blueprints/corej2eepatterns/Patterns/index.html

Microsoft Patterns and Practices http://msdn.microsoft.com/practices/topics/patterns/