Elemental Design Patterns

Jason SmithThe Software Revolution, Inc.

based on UNC PhD work, and “Elemental Design Patterns”, Addison-Wesley, 2012

Decorator (GOF)

Used to extend behavior dynamically, at run time

Like an internal plug-in system as found in a web browser

Alternative to using inheritance to provide all possible combinations of behaviors

Decorator informally

Decompose DecoratorObjectifier

Zimmer, 1995

Allows a single object interface to represent multiple concrete implementations

Client requests a method to be invoked via the objectifier interface

Client cannot know which of the concrete method bodies will execute and provide the service

Objectifier

Decompose DecoratorObject Recursion

Woolf, 1998

Chains two objects with related types

Object recursion uses Objectifier as the backbone of its form…

Adds a link between one of the concrete implementations and the interface

Uses the link to invoke the same method --to “recurse” in a sense, but on a different (related) object

Object Recursion

So Decorator can be described in

terms of composing smaller pieces

Are these pieces as small as they can

be?

Perhaps there is more “downward” to

go

Where is the bottom of this abstraction

pile?

Turtles all the way down

Turtles all the way down

So Decorator can be described in

terms of composing smaller pieces

Are these pieces as small as they can

be?

Perhaps there is more “downward” to

go

Where is the bottom of this abstraction

pile?

Turtles all the way down

So Decorator can be described in

terms of composing smaller pieces

Are these pieces as small as they can

be?

Perhaps there is more “downward” to

go

Where is the bottom of this abstraction

pile?

EDP

Turtles all the way down

So Decorator can be described in

terms of composing smaller pieces

Are these pieces as small as they can

be?

Perhaps there is more “downward” to

go

Where is the bottom of this abstraction

pile?

EDP

Elemental design patterns

decorator

object recursio

n

objectifier

Pattern Descriptions

Solution

• structure• implementation• sample code

Problem

• intent• motivation• known uses

Context

• applicability• consequences• related patterns

Hard to fit: participants, collaborations

Design Pattern A common solution to a common problem within a particular context

Participants, Collaborations are parts and relationships

Relationships form the core of design

Design of a car is more than a piles of pieces… engine, tires, transmission, seats

Design shows how the parts relate… connect, interact, work of one affects function of another

Parts list gives components

Relationships tell how parts function in concert to win over the entropy of the pile

Relationships

What is smallest relationship we can define?

A single concept connection between two things

Look for such among the entities in OO programming

Means we have to decide…

what are the conceptual entities in OO programs?

Relationships

Goal: detect elemental relationships automatically, if we can

Goal: compose elemental patterns to get higher patterns (automatically, if we can)

Higher pattern means more complex, harder to find patterns

Pause… for directions

Different relationships, different purposes

Scoping relationships give context

Scope is how an element is made unique among all other elements in the system

class Menu in package GUI_Elements is not the same thing as

class Menu in package Restaurant_Items

Scope: an enclosing something that has a name, in which you define something new

Contextual Relationships

Class: scope for methods and fields it defines

Package/namespace: scope for all in it

Method/function: scope for local variables

Access an element: specify the scopes from outer level in

◦ Implicit notation: No scope for locals in a method, or another method in same class

◦ Differing notation:

GUI_Element::Menu vs. aMenu.anItem

Context: Scope

We now have scope relationships… what else can we form relationships between?

Classes, their fields and methods…. not much else

What about objects? Different from classes?

Classes do two things

◦ Type information… member methods and fields that will exists separately in each object created

◦ Global shared fields… “static” class methods and fields

Class is really a type with an object (for global)

Relationships… what else?

Fields, Methods, Objects, Types OO entities we characterize relationships among

FMOT

Object Method Field Type

Object Defines Defines Defines Defines or Is of type

Method N/A Defines orMethod call

Defines orField use

Defines orReturns of type

Field N/A State change

Cohesion Is of type

Type Defines Defines Defines Defines orsubtyping

Fields, Methods, Objects, Types Defines is a scope relationship

FMOT

Object Method Field Type

Object Defines Defines Defines Defines or Is of type

Method N/A Defines orMethod call

Defines orField use

Defines orReturns of type

Field N/A State change

Cohesion Is of type

Type Defines Defines Defines Defines orsubtyping

OO Entity InteractionsFMOT Non-scoping

Object Method Field Type

ObjectIs of type

MethodMethod call Field use Returns of

type

Field State change

Cohesion Is of type

Typesubtyping

Terminologymethod call

o . f( ) calls p . g( )enclosingobject

enclosingobject

Callingmethod

Calledmethod

EDP Basicsin UML

A B

b: B

f()

g()h()

b.g()

class A { B b; f ( ) { b.g(); }}class B { g ( ) { } h ( ) { }}main ( ) { A a; a.f();}

EDP Basicsin Code

More EDPsDeputized Redirection

More EDPsRecursion

First Four EDPs

dissimilar

Conglomeration

Recursion

Delegation

Redirection

similar

dissimilar

similar

methodsimilarity

object similarit

y

s-calculus ◦ Abadi and Cardelli, “A Theory of Objects”, 1998◦ Computation model for OO programs◦ Object form of l-calculus

r-calculus◦ Modification and extension for patterns◦ Operators for reliances◦ J. Smith, 2004

Theoretical Foundations

Another Example

Focus on OO programming concepts, not OO language constructs

a.f() calls b.g(), then b.g() calls c.h() We can see that a.f() does not call c.h() (a

structural relationship)

However a.f() relies on c.h() to execute correctly in order for f to complete its work

So there is a reliance between a.f() and c.h() (conceptual, not structural)

Reliances

Zimmer, W. Relationships between design patterns. In J.O. Coplien and D.C. Schmidt, eds., Pattern Languages of Program Design. Addison-Wesley, Voston, 1995, pp. 345-364.

Woolf, B. The object recursion pattern. In N. Harrison, B. Foote, and H. Rohnert, eds., Pattern Languages of Program Design 4. Addison-Wesley, Boston, 1998, pp. 41-52.

References

Decorator (GOF)

Decorator in PIN

Abstract Factory

Factory Method

Decorator

Proxy

Chain of Responsibility

Template Method

Create Object

Retrieve

Inheritance

Abstract Interface

Delegation

Redirection

Conglomeration

Recursion

Revert Method

Extend Method

Delegated Conglomeration

Redirected Recursion

Trusted Delegation

Trusted Redirection

Deputized Delegation

Deputized Redirection

Fulfill Method

Retrieve New

Retrieve Shared

Objectifier

Object Recursion

Similarity Space A1

Similarity Space A2

Standard PINbox

Expanded PIN Instance

SPQR Flow

Analysis of Design Pattern Structure in OO Source

Code

Jason SmithIBM Watson Research

Our Goals

• Provide tools to software engineers to aid in the efficient comprehension of existing code bases (maintenance, new design with re-use)

• Provide support for development of new code that adheres to best-practices architecture

• Create metrics to compare relative comprehensibility and relative quality of system designs for analysis prior to implementation

• Why find patterns?

Design Patterns

• Abstractions of lessons learned

• GoF 1995

• Culling code down to the language-independent ideas, not implementation specifics …

• Community agreement on what gains “pattern” status

• Common vocabulary for software engineers to discuss and compare design issues, best practices, architecture and organization

“Common (agreed good) solutions to common problems”

Atop the Abstraction Stack

• Assembly mnemonics

• Procedural programming -- locality of code

• Object-oriented programming -- encapsulation of data with code

• Idioms

best language practices

• Design patterns

best design practices, language independent

Example Pattern“Composite”

Example Pattern“Composite”

In reality, they look like this …

// Composite pattern -- Structural example using System;using System.Text;using System.Collections;

// "Component"abstract class Component{  // Fields  protected string name; // Constructors  public Component( string name )  { this.name = name; } // Methods  abstract public void Add(Component c);  abstract public void Remove( Component c );  abstract public void Display( int depth );}

// "Composite"Class Composite : Component{  // Fields  private ArrayList children = new ArrayList();  // Constructors  public Composite( string name ) : base( name ) {}  // Methods  public override void Add( Component component )  { children.Add( component ); }  public override void Remove( Component component )  { children.Remove( component );}  public override void Display( int depth )  { Console.WriteLine( new String( '-', depth ) + name );    // Display each of the node's children    foreach( Component component in children )      component.Display( depth + 2 );  }}

// "Leaf"class Leaf : Component{ // Constructors  public Leaf( string name ) : base( name ) {}  // Methods  public override void Add( Component c )  { Console.WriteLine("Cannot add to a leaf"); }

  public override void Remove( Component c )  { Console.WriteLine("Cannot remove from a leaf"); }

  public override void Display( int depth )  { Console.WriteLine( new String( '-', depth ) + name ); }}

public class Client{  public static void Main( string[] args ) {    // Create a tree structure    Composite root = new Composite( "root" );    root.Add( new Leaf( "Leaf A" ));    root.Add( new Leaf( "Leaf B" ));    Composite comp = new Composite( "Composite X" );

    comp.Add( new Leaf( "Leaf XA" ) );    comp.Add( new Leaf( "Leaf XB" ) );    root.Add( comp );

    root.Add( new Leaf( "Leaf C" ));

    // Add and remove a leaf    Leaf l = new Leaf( "Leaf D" );    root.Add( l );    root.Remove( l );

    // Recursively display nodes    root.Display( 1 );  }}

// Purpose. Composite // Strategy. Use recursive composition // to create a heterogeneous aggregate#include <string.h> // that can be treated homogeneously.enum NodeType { FileT, DirT }; //int g_indent = 0; // Benefit. No more type checking and // type casting (coupling between Dirclass File { // and File is gone, Dir is onlypublic: // coupled to abstract base class) File( char* n ) { type_ = FileT; strcpy( name_, n ); } class AbsFile { NodeType getType() { return type_; } public: void ls() { virtual void ls() = 0; for (int i=0; i < g_indent; i++) protected: cout << ' '; char name_[20]; cout << name_ << endl; } static int indent_;private: }; NodeType type_; int AbsFile::indent_ = 0; char name_[20];}; class File: public AbsFile { public:class Dir { File( char* n ) {public: strcpy( name_, n ); } Dir( char* n ) { type_ = DirT; void ls() { strcpy( name_, n ); total_ = 0; } for (int i=0; i < indent_; i++) NodeType getType() { return type_; } cout << ' '; void add( File* f ) { cout << name_ << endl; } files_[total_++] = f; }; } void ls() { class Dir : public AbsFile { for (int i=0; i < g_indent; i++) public: cout << ' '; Dir( char* n ) { cout << name_ << ":" << endl; strcpy( name_, n ); total_ = 0; } g_indent += 3; void add( AbsFile* f ) { for (int i=0; i < total_; i++) files_[total_++] = f; } if (files_[i]->getType() void ls() { == DirT) for (int i=0; i < indent_; i++) ((Dir*) files_[i])->ls(); cout << ' '; else cout << name_ << ":" << endl; files_[i]->ls(); indent_ += 3; g_indent -= 3; } for (int i=0; i < total_; i++)private: files_[i]->ls(); NodeType type_; indent_ -= 3; } char name_[20]; private: File* files_[10]; AbsFile* files_[10]; int total_; int total_;}; };

void main( void ) void main( void ){ { Dir one("1"), two("2"), thr("3"); Dir one("1"), two("2"), thr("3"); File a("a"), b("b"), c("c"), File a("a"), b("b"), c("c"), d("d"), e("e"); d("d"), e("e"); one.add( &a ); one.add( &a ); one.add( (File*) &two ); one.add( &two ); one.add( &b ); one.add( &b ); two.add( &c ); two.add( &c ); two.add( &d ); two.add( &d ); two.add( (File*) &thr ); two.add( &thr ); thr.add( &e ); thr.add( &e ); one.ls(); one.ls();} }

Or this…

Or this…

(defgeneric add-dependent (dm dependent &amp;optional recursivep) ;; see below for the optional args (:documentation &quot;Add DEPENDENT as a dependent of DM. Return DM&quot;))

(defgeneric delete-dependent (dm dependent &amp;optional recursivep) (:documentation &quot;Remove DEPENDENT from DM. Return DM&quot;))

;;; No DELETE-DEPENDENT-IF

(defgeneric map-dependents (f dm) (:documentation &quot;Map F over the dependents of DM. Return DM&quot;))

;;; No cursors.

(defgeneric make-collection-for-dependent-mixin (dm))

(defclass dependent-mixin () ;; something that has dependents. We expose the DEPENDENTS slot. ((dependents :reader dependents-of)))

(defmethod make-collection-for-dependent-mixin ((dm dependent-mixin)) (make-instance 'simple-childed-mixin))

(defmethod initialize-instance :after ((dm dependent-mixin) &amp;key) (setf (slot-value dm 'dependents)

(make-collection-for-dependent-mixin dm)))

(defmethod add-dependent ((dm dependent-mixin) dependee &amp;optional recursivep)

(declare (ignorable recursivep)) (add-child (dependents-of dm) dependee) dm)

(defmethod delete-dependent ((dm dependent-mixin) dependee &amp;optional recursivep)

(declare (ignorable recursivep)) (delete-child (dependents-of dm) dependee) dm)

(defmethod map-dependents (f (dm dependent-mixin)) (map-over f (dependents-of dm)) dm)

A solution must be language independent

Patterns “Intertwingled”

All non-trivial designs involve many cross-mixed patterns

Same class might be a component in 4 or 5 patterns

Prior Approaches

• GoF patterns are too large to formalize flexibly

• “Mini-patterns” have been tried but still at too large a graularity

• Cannot handle implementation variances, due to static definitions of patterns… no inference capabilities

Elemental Design Patterns

• GoF patterns are too large to formalize flexibly

• Divide and conquer… define “bricks” and “wall construction procedures”

• Call them Elemental Design Patterns ( EDP )

• Idea is for EDPs to be easy to find in code

• Use resolution theorem prover to do the “wall assembly”

• Add to the assembly methods rules that allow flexible variations on basic definitions

Mini-Pattern: Objectifier

Mini-Pattern: Object Recursion

Relationships

Relationships are the key

Method calls: relationships between functions

Field access: relationships between objects

Inheritance: relationships between types

Objects, Types, Methods, Fields…

What else is there in OO? That’s it…

SPQR System

Source code

gcc parse treegcc

object XML

gcc2poml

poml2otter

Source-code-specific otter clauses

Rho calculus compos rules EDP catalog

Otter theorem prover

Found patterns report

python

Otter proofs

EDP Catalog

Object element EDPsCreateObj AbsInterface Retrieve

Type Relation EDPsInheritance

Method Invocation EDPsRecursion RedirectedRecursion Redirect RedirectInFamily RedirectInLimitedFamilyDelegate DelegateInFamily DelegateInLimitedFamilyConglomeration DelegatedConglomerationExtendMethod RevertMethod

Redirect In Family

Composing EDPs

• Successful in composing the EDPs to define 22 of the 23 GoF patterns

• Can produce many other described patterns as well from the literature

and mini’s… Objectifier, ObjRecursion

• 23rd GoF pattern is Iterator …Really a language construct, not a pattern

Is an operation for a data type

Formalization

• Begin with s-calculus ( OO analog to l-calculus )

• Add ability to encode relationships between constructs with reliance operators … gives r-calculus

Describe relationships between objects, methods, and fieldsTransitive

A<<B, B<<C : A<<C

• Define EDPs directly in r-calculus

• Express more complex patterns as compositions and assemblies of EDPs

• Encode it all as Otter clauses

SPQR System

Source code

gcc parse treegcc

object XML

gcc2oml

oml2otter

Source-code-specific otter clauses

Rho calculus compos rules EDP catalog

Otter theorem prover

Found patterns report

python

Otter proofs

“Isotopes”

• Flexibility requires capturing variations on a basic pattern

• Static definition/specification cannot capture the many different detailed forms code may take and still be judged a “pattern instance”

• Implementation may differ, clutter may be more or less, extra objects may be imposed, but

the base roles appear,

their relationships stay the same

Redirect In Family

Redirect In Family Isotope

Evaluation

• Code trials

• Problem from Evans and Sutherland

• C++ standard library analysis for EDPs

• Working code from previous projects (OvalTine)

E&S Industrial Code

Rho Calculus Definitions

Found Patterns

Object Recursion - Annotated

Decorator Pattern

Decorator - Annotated

SPQR Tool Sequence

Extension via Training

• Hundreds of patterns are named and in use

• How do we get these into the formal dictionary? Must a programmer be a r-calculus expert?

• New patterns can be added via “training”

• Write a canonical program that contains the necessary and sufficient code components comprising the pattern ( and little else )

SPQR tools will extract the facts into r-calculusHand tune the definition and test

Other forms of Variance

• Vary by type… inheritance

• Get the photo of whiteboard

• MDL explains patterns existence

Are Patterns Arbitrary?

• Why are patterns the way they are?

• MDL explains it… GoF are minimal in several measures that make sense for software complexity

• Software Architecture

Advantages of SPQR

• Near zero learning curve

• Adding to existing tool chain, not replacing it

• Not adding to workload of engineer

• Analogous to a spelling checker or execution profiler

• Theorem prover + r-calculus + transitivity (isotopes) gives searching over infinite design space using finite number

of definitions• New way to teach OO concepts and design

Design Space 2.6

Design Space 2.7

Design Space 2.8

Design Space 3D

2D Projection of 3D SpaceMethod similarity fixed at

“similar”

2D Projection of 3D SpaceMethod similarity fixed at

“dissimilar”

Recursion

Deputized Recursion

DecoratorUML collaboration diagram

Strategyrole-annotated class diagram

Big Class Diagram

Decorator towards PIN

Decoratortowards PIN

Fulfill Method

Fulfill Method

Decorator (reprise)

Decorator base

Up a level…

4.13.a

4.13.b

4.14

4.15

4.16

4.17

4.18

4.19

4.20

4.21

4.22

4.23

Pattern