Pattern Classification Kal Vot

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Ohjelmistotuotannon Teoria

Tampere University of Technology

Software Systems Institute

Pattern Classification

Imed Hammouda & Jakub [email protected], [email protected]

10.03.2004


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Outline

Introduction

Pattern Classification Classification Criteria

Example Classification Schemas

Conclusions


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Introduction: What is a Pattern?

Each pattern is a three-part rule, which expresses a relationbetween a certain context, a problem, and a solution.[Alexander77]

Each pattern is a three-part rule that expresses a relation betweena certain context, a certain system of forces that occursrepeatedly in that context, and a certain software configuration

that allows these forces to resolve themselves. [Gabriel]

A pattern for software architecture describes a particularrecurringdesign problem that arises in specific design contexts and

presents a well-proven generic scheme for its solution. The solutionscheme is specified by describing its constituent components, theirresponsibilities and relationships, and the ways in which theycollaborate. [Buschmann96]


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Pattern Classification

The increase in the number of patterns made it very important todevelop proper methodologies and techniques how to organize

them.

Pattern classification is the organization of patterns into groups ofpatterns sharing the same set ofproperties.

The kind of these properties is not fixed and may include criteriasuch as structure, intent, or applicability.

Depending on the chosen criteria, we could define a classificationschema.

Pattern classification techniques


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Dimensions of Classification

Schemas Different classification schemas can have different

dimensions.

A two dimensional schema, for example, uses two

criteria in the classification process.

Usually, the more dimensions a schema has, the more

useful the classification is.

Better partitioning of the pattern space


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Dimensions of Classification

Schemas The same pattern can have different kinds of properties,

it can be included in more than one category.

Each property maps the pattern to the category of that

property kind.

In order for the classification to be efficient, we think that

a pattern should not belong to more than two categories.

Hint: Concentrate on the major attributes of patterns.


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Purpose of Pattern Classification

The main goal of pattern classification is to make it easier for

software developers to select the right pattern to apply.

Example: In order to solve a certain design problem, the right

design pattern, if available, should be selected.

For selecting a specific pattern, i.e. pattern selection, the nature of

the problem should be matched with the right pattern category.

Hint: Match the description of the problem with the description ofthe pattern category, then with the description of the individual

patterns.


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Purpose of Pattern Classification

Classification schemas can be used to understand and

perceive the main properties of patterns.

It is usually impractical to go through all the details of all

the patterns before picking up the right pattern.

Classification schemas can be used to structure a

pattern system and highlight the relationships betweenthe constituent patterns.


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Properties of Classification Schemas

According to [Buschmann96]: Simple and easy to learn: It should be easy to use the classification

scheme to classify and select patterns.

Few classification criteria: In order to reduce complexity and ambiguity,the classification schema needs to be as compact as possible in terms ofthe number of criteria.

Reflecting pattern properties: Using the classification schema, it shouldbe possible to represent the main properties of the patterns to beclassified.

Roadmap to pattern selection: The classification scheme should easethe pattern selection process.

Openness to the integration of new patterns: Using the classificationschema, it should be possible to classify new patterns.


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Properties of Classification Schemas

Additional Properties:

Openness to new classification criteria: It should be possible to

extend the classification scheme by either increasing its

dimension or by modifying a given dimension.

Reflecting the relationship between patterns: In addition tocapturing their main properties, the classification schema should

be able to highlight the relationships between the patterns.


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Pattern Classification Criteria

Discipline Scope

Criteria

Granularity

Domain Purpose

Paradigm


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Classification by Discipline:

Example

A pattern system for conservation economy [ConservationEconomy04]


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Classification Criteria: Domain

In software engineering, patterns are mostly known for, but not

restricted to, solving problems of design and architecture.

Different patterns have been proposed to solve design problems in

various areas of software engineering.

Patterns have been applied in the domain of real-time systems,

communications, distributed systems, user interface, embedded

systems, etc.

Software developers tend to select patterns within the category

matching theirspecific problem domain.


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Classification Criteria: Paradigm

Patterns became a popular practice in the development ofobject-

oriented software systems.

Patterns apply to other paradigms as well. Imperative languages

may provide their own imperative patterns.

In the object oriented paradigm, patterns are described in terms of

concepts like objects, classes, object composition, and class

inheritance.

In imperative programming, patterns are mainly expressed in terms

of other concepts such as functions and procedures.


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Classification by Paradigm:

ExampleA pattern catalogue for functional logic languages: [Antoy02]

Ensure that values of a datatype are

hidden.

Opaque Type

Ensure that a local name is globally

unique.

Locally Defined Global

Identifier

Compute solutions in an incremental

manner.

Incremental Solution

Ensure that a mapping from indexes to

values is injective.

Concurrent Distinct Choices

Prevent invoking a constructor that

might create invalid data.

Constrained ConstructorIntentPattern


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Classification Criteria: Granularity

Patterns in a software system can be categorized

depending on the level at which they address the

system.

It is sometimes difficult to draw the border line between

different pattern categories.

The same pattern could be classified in differentgranularity categories.


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Classification by Granularity:

Example Widely used granularity-based classification:

[Buschmann96]

Architectural patterns: refer to a software system at high level.

Design patterns: focus on subsystems and components.

Idioms (coding patterns): address the lowest level of a software

system.


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Classification Criteria: Purpose

An efficient method to classify patterns is to categorize

them according to theirpurpose.

The purpose represents the kind of problems the pattern

solves.

This criterion is the most useful since it describes the

concrete situation where the pattern applies.


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Classification by Purpose: Example

For designing real-time frameworks, the followingpurposes are defined: [Douglass99] Architectural support patterns: represent the strategic decisions

for the organization of real-time applications.

Collaboration and distribution:patterns provide solutions to

common application domain problems in real-time systems.

Safety and reliability patterns: deal with common problems ofsafety and reliability.

Behavioral patterns: provide different implementation solutionsinvolving multiple objects.


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Classification Criteria: Scope

Patterns can then be classified according to the features

implementing them.

Such a classification criteria is known as scope.

In the object-oriented paradigm, design patterns can be

implemented using either object composition or class

inheritance.


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Classification by Scope: Example

GOF classification uses the scope criterion: [Gamma95]

Class representation: uses class inheritance.

Object representation: uses object composition.

The same pattern might be implemented either way.

Example: Adapter.


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Example Classification: GOF

The design patterns catalogue presented in [Gamma95]

is one of the most widely known pattern classification

schema.

GOF classification is two dimensional.

Patterns are classified by theirpurpose and scope.


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Example Classification: GOF

Purpose:

Creational: related to object creation.

Structural: concerning structures (compositions) created by

classes and objects.

Behavioral: deal with the way responsibilities in classes are

distributed.

Scope:

Class representation: uses class inheritance. Object representation: uses object composition.

l f l


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GOF Classification: Singleton

Purpose: Creational

Scope: Object

Singleton

static Instance()

SingletonOperation()GetSingletonData()

static uniqueInstance

singletonData

return uniqueInstance

Ensure that only one object of given class is created

l ifi i d


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GOF Classification: Adapter

Purpose: Structural

Scope: Object or Class

TextShape

BuildingBox()

CreateManipulator()

Line

BuildingBox()

CreateManipulator()

DrawingEditorShape

BuildingBox()

CreateManipulator()

TextView

GetExtent()

return text -> GetExtent()

return new TextManipulator

Convert the interface of a class into another interface clients expect

GOF Cl ifi i S


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GOF Classification: Strategy

Purpose: Behavioral

Scope: Object

Composition

Traverse()

Repair()

Compositor

Compose()

compositor -> Compose()

SimpleCompositor

Compose()

TeXCompositor

Compose()

ArrayCompositor

Compose()

Define a family of algorithms, encapsulate each one,

and make them interchangeable

E l Cl ifi i B h


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Example Classification: Buschmann

The work of Buschmann classifies patterns using two

criteria: [Buschmann96]

Buschmann classification is two dimensional.

Patterns are classified by theirgranularity (pattern

categories) and purpose (problem categories).

E l Cl ifi i B h


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Granularity:

Architectural patterns: specify the fundamental structure of

applications. They specify structure of the system as subsystems,and their responsibilities, and define rules for relationships

between them.

Design patterns: focus on subsystems and components, the

middle level of a software system. Design patterns describe

common problems arising in a given context of particular

subsystem.

Coding patterns (idioms): use proven conventions and

techniques during the implementation phase of applications.


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E l Cl ifi i B h


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Purpose:

Organization of work patterns define solutions for solving complex

services through component collaboration.

Access control patterns manage access to services.

Management patterns handle the management of collections ofhomogeneous objects, services, and components.

Communication patterns manage the communication between

components.

Resource handling patterns manage shared components and objects.

B h Cl ifi ti


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Buschmann Classification:

Blackboard Granularity: Architectural.

Purpose: From mud to

structure.

Blackboard

inspect

update

solutions

controlData

Control

loop

nextSource

Knowledge

Source

updateBlackboard

execConditionexecAction

operate on

activates

+1

+1

Several specialized subsystems assemble their knowledge

to build a possibly or approximate solution

Zi Cl ifi ti


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Zimmer Classification

Zimmer Classification [Zimmer95] : New classification of

the GOF design patterns.

Three kinds of relationship between patterns defined:

Pattern X uses pattern Y in its solution.

Pattern X is similarto pattern Y.

Pattern X can be combined with pattern Y.

These relationships describe new classification schemafor the GOF design patterns.


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Domain Dependent Patterns J2EE


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Domain-Dependent Patterns - J2EE

J2EE design patterns can be implemented only in J2EE

technology.

Domain specific patterns may be based on other

patterns Session Facade is based on the GOF

Facade design pattern.

They also may be completely domain dependent

Value Object J2EE design pattern.

Session Facade Example


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Session Facade Example

Clients directly accessing application components must deal with

complexity of the implementation.

Changes in the internal implementation affect clients.

High number of calls needed to achieve a task.

Client

Client

Client

Network

Application Server

Access Without Faade [Marinescu02]

Session Facade Benefits


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Session Facade - Benefits

Access involving Session Faade:

Application internal complexity is hidden.

Changes in the internal implementation do not affect clients. Number of calls is reduced.

Client

Client

Client

Application Server

Fac

ade

Facade

Network

Access With Faade [Marinescu02]

Process Patterns


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Process Patterns

Address the problem ofstructures and processes in organisations

especially in domain of software development. [Coplien94]

Applicable to whole organisations or only particularprojects.

Used in many aspects of organisation structure:

Size of the organisation.

Tasks scheduling.

Assigning tasks to organisation (project) members.

Information flow. Assuring quality level.

Process Patterns Example 1


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Size of the organization pattern:

Answers the question how big should be the organisation (project

group) for creation a product of 25000 lines of code.

Considerations:

Too small organisation may not be able to deal with a task. Too big organisation may not be profitable enough at the beginning and

may face communication problems.

Solution: Create a team of about 10 selected members that number should

ensure enough workforce, but should not affect communication and

profit margins.



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Solo Virtuoso pattern:

Addresses small projects not likely to grow rapidly.

Considerations:

Too big team may be too costly to maintain when the project is small.

Solution:

The team should be based on one or two members that are specialists in

the domain.

Possible problems:

Absence of even one team member may cause challenges to the

project.



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Firewalls pattern:

Addresses communication problems between the team

and the outside world.

Considerations:

Developers are being directly contacted too often by theoutsiders - this distracts developers.

Information flow from the outside world must be maintained .

Solution: A manager role who shields developers from direct contact from

outside, but sustains the information flow.

Analysis Patterns


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Analysis Patterns

Analysis patterns are used to analyse organisations

structures and processes in order to model them in

software. [Fowler97]

Some Analysis Patterns may be applicable only to one

domain (e.g. health care) but many can be used invarious domains.

Analysis Patterns Classification


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Analysis Patterns Classification

Analysis Patterns can be classified in following groups:

Accountability describing relations between parties

(organisations, people). Observations and measurement used to record information

about the world.

References to objects how unique to objects in real life can be

created.

Accounting used in accounting systems.

Planning planning and recording of resources use.

Trading used for trade analysis (e.g. the influence of changingprices on profits).

Analysis Patterns - Party


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Analysis Patterns Party

The Party analysis pattern addresses the problem of

relating information (phone number, email etc.) to

many parties (people or organisations), which are

similar to each other.Telephone

Number

Person

Organization

Party Address

PersonZero or more [0,*] Zero or one [0,1]

Party Analysis Pattern

Analysis Patterns - Quantity


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Analysis Patterns Quantity

The Quantity pattern deals with problem of storing

measurement results.

Results stored only as values may be difficult to interpretand prone to conversion errors.

Without the Quantity pattern the values are interpreted

based on an explicit contract with the client.Person

height: Number

weight: Number

blood glucose level: Number

Measurement Without Quantity

Analysis Patterns - Quantity


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Analysis Patterns Quantity

The Quantity analysis pattern advocates storing valuesalong with units.

Measurement results can be stored in units that were usedin the measurement.

Conversion rules to other units are stored with the results

Results are not ambiguous.Person

height: Quantity

weight: Quantity

blood glucose level: Quantity

Quantity

amount: Number

units: Unit

+, -, *, /, =, >,

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