FRP Presentation Web

Functional Relational ProgrammingWaging War on Complexity

SPA 2006

Ben [email protected]

Peter [email protected]

mailto:[email protected]



Ben Moseley & Peter Marks SPA 2006

OverviewPart 1: Complexity

Types of complexity

Sources of complexity

Part 2: Functional Relational Programming

Functions & Relations

High-level architecture

Worked Example


ConclusionsState is the root of all evils

Much complexity in our software is non-essential

Constraining our systems to only explicitly possessing essential state offers great promise in helping to control complexity

Separating non-essential control from essential logic reduces system complexity

FRP looks interesting and worth finding out more about

most


“The complexity of software is an essential property”

Fred Brooks, “No silver bullet”, 1987


Complexity curve

Development

Com

ple

xit

y


Accidents and Essence

Essential Complexity is inherent in, and the essence of, the problem

Accidental Complexity is associated with building a system to solve the problem


What was wrong with 4GLs?

They weren’t very good languages

Did not make the paradigm shift

Hardware wasn’t fast enough

Degenerated to bad 3GLs

… but RDBMSs and Spreadsheets exploded


Manifestations of Complexity

State

Control

Code Volume

Expression


Example: Quick Sort

qsort( int a[], int lo, int hi ) {

int h, l, p, t;

if (lo < hi) {

l = lo;

h = hi;

p = a[hi];

do {

while ((l < h) && (a[l] <= p))

l = l+1;

while ((h > l) && (a[h] >= p))

h = h-1;

if (l < h) {

t = a[l];

a[l] = a[h];

a[h] = t;

}

} while (l < h);

t = a[l];

a[l] = a[hi];

a[hi] = t;

qsort( a, lo, l-1 );

qsort( a, l+1, hi );

}

}

Duplication

Arbitrary order

Transient state

Missing abstraction

Optimisation to sort in place

Poor naming

Arbitrary order

X

Unclear: should not include hi

Specific algorithm


Activity: Wood and Trees

Working in groups of four

Examine a non-trivial software system

Distill its essence then focus on what remains

Attribute the accidents…


Accidental Complexity

StateWhat can be derived?What is purely transient?ControlWhen is order unimportant?ExpressionDuplication or redundancyInconsistency (particularly of idiom)Missing abstractionUnnecessary abstraction


Activity: Thinning

Classify accidental complexity instances

Platform

Language

Effluent – unwanted byproduct

End of Part 1


Part 2 - Overview

Review of Complexity

Functional Relational Programming

Functions & Relations

High-level architecture

Worked Example

Exercise & Discussion

14

Accidental Essential

Complexity Review

Accidental Complexity Essential Complexity

??


InfrastructureInfrastructureInfrastructureInfrastructure

Desired Architecture

Accidental

Essential


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oobjbjoobjbj

oobjbjoobjbj

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oobjbjoobjbj

...NO!!

Objects...?


Functional Programming

Pure FP avoids state completely

Better to think of FP as a useful technique rather than a group of languages

Immutability

Passing and returning Functions

Advantages: Reasoning, Expressivity, Speed


Relational ModelFamiliar from database world ...

...but... Relational Model ≠ SQL !!!

Powerful and flexible

Sound mathematical foundation

name groupgroup dob

ben 7 21/05/74sam 4 03/05/81jon 3 17/06/92

mark 4 12/11/89


dob groupgroup name

21/05/74 7 ben

03/05/81 4 sam

17/06/92 3 jon

12/11/89 4 mark

dob groupgroup name

17/06/92 3 jon

12/11/89 4 mark

21/05/74 7 ben

03/05/81 4 sam

name groupgroup dob

ben 7 21/05/74

sam 4 03/05/81

jon 3 17/06/92

mark 4 12/11/89

Structural component is based on Sets

So, no duplicates & ordering irrelevant

name groupgroup dob

jon 3 17/06/92

mark 4 12/11/89

ben 7 21/05/74

sam 4 03/05/81

Relational Model

name groupgroup dob

ben 7 21/05/74

sam 4 03/05/81

jon 3 17/06/92

mark 4 12/11/89


Relational Model

Structure

Manipulation (Relational Algebra - not SQL!)

Integrity

Data Independence

USERS

name groupgroup dob

ben 7 21/05/74sam 4 03/05/81jon 3 17/06/92

mark 4 12/11/89



What is FRP?

A new (as far as we know), unproven way of building large systems

Based on some old ideas

Aims for SIMPLICITY above all else

An (internal) Architecture not Language...



FRP Architecture

Accidental

Essential



FRP Architecture

Accidental

State & Control

EssentialLogic

EssentialState


FRP ArchitectureInfrastructureInfrastructureInfrastructureInfrastructure

Accidental

State & Control

EssentialLogic

EssentialState


Accidental

State & Control

EssentialLogic

EssentialState

RelationsRelations

FunctionsFunctions

Interfaces


FRP Running ExampleInfrastructureInfrastructureInfrastructureInfrastructure

Accidental

State & Control

EssentialLogic

EssentialState

Editorial system for a Journal

People submit Papers, Chief Editor posts them for Review (on private editorial website), they are Rejected / Accepted and Published

Main Entities: Paper, Journal

Each Paper conceptually has a lifecycle...


PaperLifecycle


Accidental

State & Control

EssentialLogic

EssentialState

ProposedProposedProposedProposed Under Under ReviewReviewUnder Under ReviewReview

Awaiting Awaiting CorrectionCorrection

ss

Awaiting Awaiting CorrectionCorrection

ss

RejectedRejectedRejectedRejected

PublishePublishedd

PublishePublishedd

AcceptedAcceptedAcceptedAccepted

(“State” Transition Diagram)(“State” Transition Diagram)(“State” Transition Diagram)(“State” Transition Diagram)


Essential StateInfrastructureInfrastructureInfrastructureInfrastructure

Accidental

State & Control

EssentialLogic

EssentialState

This consists solely of definitions of Relations representing the user’s inputs to the system

Basically just a schema for the inputs

The whole system will be driven by users updating these input relations at runtime

No Derived values here (since not “essential” they be stored rather than rederived)


PAPER

paper authorauthor submitted

DB Theory ian 21/05/06Pi Calculus sam 03/05/06

OODBs tim 17/06/06Ruby On Rails bob 12/11/06

POSTING

paper posted

DB Theory 23/05/06Pi Calculus 05/05/06

Ruby On Rails 15/11/06

OPINION

paper reviewerreviewer opinion

DB Theory adam GOODDB Theory fred BADPi Calculus adam GOODPi Calculus fred GOODPi Calculus simon GOOD

Ruby On Rails adam GOODRuby On Rails fred GOODRuby On Rails simon GOOD

JOURNAL

issueissue paper

17 Pi Calculus18 Ruby On Rails

Essential State Example InfrastructureInfrastructureInfrastructureInfrastructure

Accidental

State & Control

EssentialLogic

EssentialState


Essential LogicInfrastructureInfrastructureInfrastructureInfrastructure

Accidental

State & Control

EssentialLogic

EssentialState

Definitions of Derived Relations

i.e. intermediate and output relations

Defined in terms of Essential State relations

Uses relational algebra (not SQL!)

Uses (pure) user-defined functions

Essentially similar to View defns in an RDBMS



Accidental

State & Control

EssentialLogic

EssentialState

Integrity Constraints

Not concerned with State at all (eg provides no facilities for manipulating State)


Essential Logic Example InfrastructureInfrastructureInfrastructureInfrastructure

Accidental

State & Control

EssentialLogic

EssentialState

OPINION




OVERVIEW = project(OPINION, paper opinion)

OVERVIEW

paper opinion

DB Theory GOODDB Theory BADPi Calculus GOOD

Ruby On Rails GOOD



Accidental

State & Control

EssentialLogic

EssentialState

OPINION




BAD_OPINIONS = restrict(OPINION | opinion == BAD)

BAD_OPINIONS

paper reviewer opinion

DB Theory fred BAD



Accidental

State & Control

EssentialLogic

EssentialState

REJECTED = project(BAD_OPINIONS, paper)

BAD_OPINIONS

paper reviewer opinion

DB Theory fred BAD

REJECTED

paper

DB Theory



Accidental

State & Control

EssentialLogic

EssentialState

OPINION




GOOD_OPINIONS = restrict(OPINION | opinion == GOOD)

GOOD_OPINIONS


DB Theory adam GOODPi Calculus adam GOODPi Calculus fred GOODPi Calculus simon GOOD



ACCEPTED = minus(project(GOOD_OPINIONS, paper), REJECTED)





Accidental

State & Control

EssentialLogic

EssentialState

GOOD_OPINIONS


DB Theory adam GOODPi Calculus adam GOODPi Calculus fred GOODPi Calculus simon GOOD


REJECTED

paper

DB Theory

ACCEPTED...

paper

DB Theory

Pi CalculusRuby On Rails

ACCEPTED

paper

Pi CalculusRuby On Rails



Accidental

State & Control

EssentialLogic

EssentialState

SCORE

paper reviewerreviewer score

DB Theory adam 98%DB Theory fred 48%Pi Calculus adam 79%Pi Calculus fred 73%Pi Calculus simon 74%

Ruby On Rails adam 83%Ruby On Rails fred 89%Ruby On Rails simon 77%

OPINION

paper reviewerreviewer score opinion

DB Theory adam 98% GOODDB Theory fred 48% BADPi Calculus adam 79% GOODPi Calculus fred 73% GOODPi Calculus simon 74% GOOD

Ruby On Rails adam 83% GOODRuby On Rails fred 89% GOODRuby On Rails simon 77% GOOD

opinion=opinionFromScore(score))

OPINION =extend(SCORE,



Accidental

State & Control

EssentialLogic

EssentialState

Comprised of:

Derived Relations

User-defined functions

Constraints

No State, no Control


Accidental State & Control (ie Performance)


Accidental

State & Control

EssentialLogic

EssentialState

Basically this is just a configuration file:

Declarative specification of where State should be used

Declarative specification of what Control should be used (eg which bits should be eager, which lazy)

Has NO affect whatsoever on the logic (i.e. correctness) of the system


InfrastructureInfrastructureInfrastructureInfrastructureInfrastructure

Accidental

State & Control

EssentialLogic

EssentialState

Completely independent of all the rest of the system - totally “system-agnostic”

Can be written fairly easily in any language (eg 2000 LOC Java, 1500 LOC Scheme)

Determines what performance settings are available to the Accidental component

May provide type-checking, basic functions etc


Activity - DVD Rentals

System to manage DVD Store:

Give info about Stock

Give info about Rentals

Assume the existence of any useful function

Don’t worry about Syntax!


SPA 2006

Ben [email protected]

Peter [email protected]

et

Documents

FRP Presentation Web