Semantics in Declarative SystemThe Evolution of Business Unit Empowerment

Dan McCrearyDan McCreary & Associates

Wednesday, 5/23/2007 8:00 AM - 9:00 AM

Level: Business/Strategic

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Presentation Summary

“Declarative programming” has become the latest buzzword to describe languages that abstractly define systems requirements (the what) and leave the implementation (the how) to be determined by an independent process. This makes the semantics (meaning) of declarative data elements even more critical as these systems are shared between organizations. This presentation:

– Provides a background of declarative programming

– Describes why understanding the semantic aspects of declarative systems is critical to cost-effective software development

Note: All opinions stated in this paper are solely those of the author.

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Presentation Summary (cont)

– Discusses declarative and semantic aspects of common development systems such as; XHTML, CSS, XForms, XML transforms, XML Schemas, OWL, metadata registries, web services, composition, service-oriented architectures (SOA) and the enterprise service bus (ESB)

– Discusses how social networking software and Wikis are used to quickly build consensus on precise semantics

– Presents ten specific recommendations to lower costs of agile information systems

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Presentation Includes

• Definitions of declarative systems and contrasts with them with traditional procedural systems and stand-alone declarative languages

• A critical analysis of semantics in declarative systems • Case studies using XForms, Wikis and other

collaborative software• The role of social networking systems, reputation and

trust in the development of semantically precise declarative frameworks

• Specific recommendations of how organizations can be more effective by integrating semantics and declarative systems into their software development processes

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Evolution Metaphors

• Specialization of Languages

• Generalization of Languages

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Evolution: Specialization• Darwin’s Galapagos Finches• Beaks are highly adapted to different food sources • Finches adapted to specific ecological "niches“ over

millions of years of isolated evolution

• Similar to domain-specific declarative languages

See Wikipedia "Darwin's Finches"

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Evolution: Generalization

• Generalization: The Raccoon– The world has a higher population of raccoons today

due to their ability to quickly adapt to changing urban environments

– Similar to highly adaptive procedural languages

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Computer Science Abstractions

Assembly

1010001010

Fortran

FOR I = 1 TO 10 DO

Structured

Function(A, B)

Object

Class MyClass(Method MyMethod

Declarative<xf:input> <xf:label>

time

Higher abstractions

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The Software Development Process

• Requirements are about “What”• Design and Build is about “How”

Requirements(BA)

Design(Architect)

Build(Programmer)

Test(QA Staff)

Declarative Languages

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A Declarative “System” Is…• A software development system, tailored to a specific domain

(such as web applications), used to capture precise business requirements within the context of a problem domain (the implicit context)

• Declarative systems do not specify how requirements are implemented to build working systems. Declarative systems only define the requirements

• Declarative systems document requirements in specialized vocabularies and can be used to generate entire working systems including user interfaces, persistence and test data

• Declarative systems specifically omit some assumed requirements (such as system availability, performance, reliability, security etc)

A Declarative system is a set of "little languages" with precise semantics that fit together like a puzzle to solve a problem

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Computer Science Definition

• Do not confuse a “Declarative System” with the computer science language taxonomy “Declarative Language”

• “Declarative languages" are used to describe a group of programming languages and to contrast them against imperative languages.

DeclarativeLanguages

FunctionalLanguages

LogicLanguages

ConstraintLanguages

Have sub-types

See Wikipedia “Declarative Programming”

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Declarative Systems and Context

• Declarative Systems are specialized languages for capturing requirements within a specific domain

• Just as the word “play” connotes meaning based on context* (i.e. theater vs. a playground), a given vocabulary has the ability to capture requirements based on the current problem

• The vocabulary for capturing electronic form requirements (XML Schema) may not be appropriate for expressing your build process (Apache Ant)

* See: http://wordnet.princeton.edu

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HTML, CSS and SQL

• HTML, CSS, XQuery and SQL are declarative languages using these definitions

• The semantics or “meaning” of each tag in the file is determined by an external organization

• The syntax does not have to be XML

<?xml version="1.0" encoding="UTF-8"?><html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>Declarative Systems</title> </head> <body> <h1>Introduction to Declarative Systems</h1> <p class="author">Dan McCreary</p> <p class="date">April 2007</p> </body></html>

HTML

/* global CSS used by all web pages */body { font-family: Arial, Helvetica, sans-serif; font-size: 75%; margin: 0; padding: 0; width: 1000px;}h1 { color: blue; padding: 0 15px;}

CSS

-- Old expensive booksSELECT title, author, price, pubyearFROM booksWHERE price > 100 AND

pubyear BEFORE ‘1960’ORDER BY title

SQL

xquery version "1.0";<html><body><h1>Old Expensive Books</h1><ul>{for $book in doc("books.xml")//bookorder by $book/titlereturn<li> {$book /title}, {$book}/author}, {$book}/price}, {$book}/pubyear}</li>}</ul></body></html>

XQueryhttp://www.w3.org/TR/REC-html32#body

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XML Schema Sample

• Screen capture of Altova XML Spy• 30 minutes to learn graphical notation

See: http://www.altova.com/products/xmlspy/graphical_xml_schema_editor.html

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Use Case: Electronic Forms• User fills out a web-

based form• Typical requirements

may include listing of data to be gathered, data types, validation codes and data repetition patterns

• Examples:– HTML Forms– XForms– InfoPath™

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Forms Players

<html> <head> <xf:model> <xf:/model> <head> <body> <xf:input> </xf:input> </body></html>

My-XForm.xhtmlRendered

Form

XForms“Players”

XFormsExtension

Mobile Client

Forms Server

Netfront Mobile

See Wikipedia “XForms”

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What Is Declarativeness for A Context?

• Efficiency at capturing the testable business requirements in a semantically precise and concise manner

• Example: Is a field optional? Will validation of the data fail if the field is missing?

• Ability of each data element to have precise meaning over time and within organizations

Schema Drawing Tool

XML Schema File (.xsd)

XForms

xf|input:required {font-weight: bold;} xf|input:required .xf-value {background-color:#fff6af;}*:required::after {font-weight:bold; font-size:1.5em; content: "*"; color: red; }

XForms CSS tags

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Declarative Spectrum

• For any given context different “languages” have different levels of “declarativeness”

• General purpose languages are less abstract but can solve a wide variety of problems

• Declarative languages have a more narrow purpose and target a specific problem like styling a web page or selecting data

HTML

JavaAssemblyLanguage C C++

JavaScript

C#

Narrow Purpose

More Abstract

General Purpose

Less Abstract

CSS

XSL XML Schema

Apache Ant

XForms

XQuery

XQuery Update SQL

XPath

Rubyperl

Groovy

Python

XUL

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Middle-Tiers Remain Procedural

• When the interface is consistent, declarative languages flourish• Middle tiers tend to have the most variation• Wikipedia lists over 200 web application frameworks• CMSMatrix.org lists over 700 content management systems

userdatabase

declarativeness

Presentation/style(client tier)

Data definition, insert,selection and update(persistence tier)

Business Logic(middle tier)

See: http://en.wikipedia.org/wiki/List_of_web_application_frameworks and http://www.cmsmatrix.org

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The Application Development Puzzle

SemanticsConstraints

Presentation

Build

Publish

Transform

WorkflowQuery

UpdateForms

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Filling In Each PieceWith A Declarative Language

XMLSchemaCSS

HTML

ApacheAnt

MetadataRegistry

Cocoon

XSL

BPELXQuery

XQuery UpdateXForms

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Semantically Precise Vocabularies

Standard Domain

Atom/RSS Syndication/Notification

ACORD Insurance Industry Forms Data

FpML Financial Products Markup Language

FixML Banking (Financial Information eXchange)

HL7 Healthcare (now using XML)

MISMO Mortgage Industry

NIEM National Information Exchange Model (registry)

OTA OpenTravel Alliance (Travel industry)

SIF School Interoperability Framework

GJXDM US Department of Justice (registry)

XBRL XML Business Reporting Language

See: http://en.wikipedia.org/wiki/Category:XML-based_standards

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PhonePhone

Metadata Shopping Tools

AddressAddress

FirstNameFirstName

See http://niem.gtri.gatech.edu/iepd-ssgt/SSGT-SearchSubmit.do

• You don’t need to know about 100,000 SKUs to purchase 10 items from a grocery store

• Sub-schema generation tools give you exactly what you need and nothing more

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Criteria for Semantic Precision

• Is there a published standard?

• Are there ISO/IEC 11179 definitions?– concise, precise, non-circular, distinct

• Are people using it?– Do a Google search– > 100,000 and you are safe– < 10,000 and you should be concerned

Examples: filetype:owl, filetype:xsd

See “Metadata publishing” Wikipedia

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If You Use Industry Standards…You Could Be Almost Done…

• If you use industry standards…– and these standards publish their documents in XML

Schema format…– and these standards have been transformed from XML

Schema to XForms…– and you use native XML databases to store and

XQuery to report on the data…• …then sample applications have been created

and do not require additional procedural code– just change the constraints in the XML Schema and

rerun the transforms

See also: http://www.alphaworks.ibm.com/tech/purexml

See: http://www.exist-db.org

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Accessibility

Business Analysts

SMEs and GUI Tools Users

• Precisely specifybusiness requirements

• Requires data stewardshiptraining

ProceduralProgrammers

• Extend declarativevocabularies andprovide web service“glue”

Lower costs by moving routine logic maintenance to lower levels in the pyramid

ITStrategists

• Architecture andStrategy

(prevent unnecessaryprocedural code)

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Java Libraries

10,000 class and 100,000+ methods available…but which ones are relevant to your business problem?

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“Less is More” • XForms 1.1 has

only 21 XML elements

• Much of the presentation of XForms is deferred to CSS

• Event management is deferred to the XML Events

• XML binding is deferred to the XBL standard

See Wikipedia “Minimalism”

Mies van der RoheReconstruction of the

German Pavilion in Barcelona

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Learning XForms Vocabulary

1. Bind2. Case3. Input4. Instance5. Group6. Help7. Hint8. Label9. Load10.Output

11.Message12.Model13.Repeat14.Secret15.Select16.Select117.Switch18.Submission19.Submit20.Textarea21.Trigger

Source: W3C XForms Quick Reference http://www.w3.org/MarkUp/Forms/2006/xforms-qr.html

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Recognizing XForms Structures

1. Bind2. Case3. Input4. Instance5. Group6. Help7. Hint8. Label9. Load10.Output

11.Message12.Model13.Repeat14.Secret15.Select16.Select117.Switch18.Submission19.Submit20.Textarea21.Trigger

Color coding limited vocabularies can increase the speed of pattern matching.Look for advanced text editors to provide custom element coloring.

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The New Semantics of "Nutshell"

• The 1.4 release of Java 2 Standard edition increases the size of the platform by 50%, to 2,757 classes in 135 packages

• 1.5 and 1.6 add additional classes

nutshell: something of small size, amount, or scope in a nutshell : in a very brief statement

992 pages

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Procedural Programming is Not “Poison”• It would be a mistake to tell all

your procedural programmers that the programs they are creating are fundamentally evil

• The relevant questions are:- How closely does it fit the problem

domain?- Can BAs, SMEs and other non-

programmers maintain the business rules?

- What are the chances that others will be able to maintain it in future years?

- How good are the development tools for your system?

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Popular Language Have Better Tools

• Editor– Syntax coloring

• Debugger– Set breakpoints– View internal state variables

• Refactoring tools– Can recognize reoccurring

patterns and suggest alternatives

• Performance– Code profiling

demandLimited supply curve

$

quantity

Limited resource cost curve

Whuffie curve

Whuffie is a reputation basedcurrency. Prices drop asdemand increases.

The higher demand for a good debugger, the better open-source products will become.

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If You Give a Kid a Hammer…

• People solve problems using familiar tools

• People develop specific Cognitive Styles* based on training and experience

• What are we teaching the next generation of developers?

* Source: Shoshana Zuboff: In the Age of the Smart Machine (1988)

…the whole world becomes a nail

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Use Case: Build Scripts

• Instructions for compiling source code or transforming data

• Vocabulary includes terms such as build, compile, transform, copy or clean

• Examples:– Apache Ant– Apache Maven– UNIX™ make

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Use Case: Data Selection With XQuery• Ways to specify what data

you want to extract from a data set

• Typical tasks include selecting attributes (columns), filtering, restricting results and changing sort order

• Examples– Structured Query Language

(SQL)– XQuery (w3c standard)– FLOWR

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Semantics

• The science of meaning

• What you mean when you say “cat”

• How do you associate meaning with symbols (verbal, physical, textual)

• How do we know if we both mean the same thing when we use a word?

• What if a word has multiple meanings?

Reference: WordNet

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Semantic Triangle

• Symbols can only link to referents through concepts• You can not link directly from a symbol to a referent

referent

concept

symbol

“cat”

Wikipedia: Semiotic triangle

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Communication

• Communication involves exchanging symbols that describe common attributes

• A one-to-one match of attributes that describe a common symbol match implies a high precision match

“cat”

• Domestic feline• House pet• Has fur• Has whiskers• Sometimes has fleas• Chases mice

• Domestic feline• House pet• Has fur• Has whiskers• Sometimes has fleas• Chases mice

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Same symbol – different meaning

• Little match of common attributes• Low precision semantic match

“customer”

• First name• Last name• Home address• E-mail• Cell phone number• Gender

• Company name• Home office address• Branch office address• CEO name• Web site• Industry code

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High and Low Precision

• The ideal is to have a precise standard and to use the data elements exactly as they were intended

vague standardvague usage

Not-so-good

precise standardvague usage

better

precise standard precise usage

best

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Semantic Precision• Semantic mappings are relative in time and

between groups of people (organization)• Semantic variability over time

– Something that has precise meaning to you today may not have the same precise meaning a year from now

– Our memories are imperfect and change over time• Semantic variability across organizations

(project and organization)– A “customer” to one organization may denote a

person but to another organization it may denote a company

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Semantics of an XML Data Element

• A developer puts an XML data element in an xml file• The tag has some meaning and the data within the tag

has some meaning when it was created by the developer• What is the probability

– That the developer will know the same meaning of the code 47 one year later

– That another project that opens file will understand and be able to use the meaning of the tag

– Vague standards often trigger vague interpretations of the meaning of data

<code>47</code>

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Semantic Precision in Space and Time

time

space: (projects, organizations)

Small SemanticFootprint

(rapid prototype)

LargeSemanticFootprint

(long lifetimesystems)

weeks months years 10+ years

person

team

dept.

world

enter-prise

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DRY Coding, XSL and MDA• If developers can’t quickly transform it…

…they will copy it.• DRY: Don’t Repeat Yourself• Documentation

– Is always kept up to date?– Do developers communicate their intent?– JavaDoc – generated from the source code

• The tendency to copy and paste is just too common– Developers must be diligent– Budgets must be adequate– Time must be sufficient

• You can promote Model-Driven Architecture (MDA) by reducing the effort of transformation from specifications captured in declarative languages

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Use Procedural “Glue”

• XForms uses a REST interface to send XML to a server• Some XML databases (DB2 v9) sill use JDBC interfaces to insert

XML documents• Use procedural glue to build custom interfaces between systems

with incompatible interfaces

Procedural “Glue”

XQuery Update(JDBC)

XForms XML(REST)

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How Quickly Can We Create New Declarative Languages?

• Configuration files are really just small languages

• Configuration files are easy to parse, validate data using XML tools and build custom forms to use

• Easy to teach non-programmers to graphically build XML Schemas to validate XML files– Answer – About a week

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How Quickly Can We Create Consensus?

• Example: XForms standard– Work started in 2001– XForms 2.0 is still a two to three years away

• How can we accelerate this consensus building process?

What factors impact the rate that species evolve?What impact does life span have on a species?How are design ideas exchanged between species?

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Solution: Wikis and Collaboration

• How long does it take to build consensus on the semantics of a new data element?

• How many people might use this declarative language?

• The larger the stakeholder group, the longer it takes

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Parker Projection

Time

100%

RelativeCode Base

Procedural code (Java, JavaScript, VB, C#, C++)

Declarative code (XHTML, CSS, XSLT, XForms)

Source: Jason Parker, Minnesota Department of Revenue, November 2006

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Top 10 Recommendations1. Use semantically-precise declarative systems over procedural systems

when the business problem is in the right context2. Aggressively promote data stewardships within business units3. Use controlled vocabularies and metadata shopping tools to allow non-

programmers to select data elements from lists4. Separate semantics (leaf elements) from constraints (branches)5. Leverage the pattern matching portion of the brain using graphical

development tools and element-based syntax coloring editors6. Train programmers on ways to extend declarative vocabularies using

technologies such as XML Binding Language (XBL)7. Use procedural code to build interfaces between incompatible systems8. Isolate procedural by providing XML/REST service wrappers code behind

semantically precise web services9. Don’t expect your procedural programmers to jump on the declarative

bandwagon without some training10. Use social networking tools (voting, wikis) to rank and find appropriate

tags and extensions

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Unanswered Questions1. How will declarative systems evolve? Will there be a few or many?2. How quickly will declarative languages evolve? Will they continue to

specialize?3. Can we deliver entire working systems without ever leaving a single

family of standards? (see XForms/eXist and w3c example)4. What will be the impact of semantic wikis and micro-formats?5. Can individual tags stand alone or do they need to be integrated into

larger standards to be accepted?6. Will metadata shopping tools and graphical constraint tools make the

process of building entire systems accessible to mere mortals?7. Will declarative systems halt overseas out-sourcing of procedural

software developers?8. Will there be a large increase in the demand for staff that can extend

declarative systems?9. Will declarative systems allow applications to run anywhere a “Forms

Players” can run?10.Will vendors used to locking customers into proprietary APIs be

forced to compete by having more robust and more reliable execution platforms?

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Selected References• Evolution

– Charles Darwin, Origin of the Species– Richard Dawkins, The Blind Watchmaker

• Cognitive Styles– Shoshana Zuboff: In the Age of the Smart Machine (1988)

• Building Trust– Succeeding with Objects: Decision Frameworks for Project Management, Adele

Goldberg and Kenneth S. Rubin• XML Data Standards

– NIEM Concept of Operations at NIEM.gov– ISO/IEC 11179 (wikipedia)

• XForms– XForms.org, wikipedia

• Domain Specific Languages– Niel Ford, Language Oriented Programming– Martin Flowler

http://www.infoq.com/presentations/domain-specific-languages