The PIA, an XML-based platform for Web Applications

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Automatically generated 2000-02-29 18:34 by steve

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	The PIA an XML-based platform for Web Applications Stephen Savitzky Chief Software Scientist Ricoh Silicon Valley <steve@rsv.ricoh.com>
	The PIA, an XML-based platform for Web Applications

<< 1 >> contents start	Outline
	Introduction: The need for cross-platform web applications How the PIA Works: using XML in a unique way Additional PIA features
	The PIA, an XML-based platform for Web Applications

<< 2 >> contents start	Major Trends in Web Applications
	Web Applications Increasing Interactivity and Customizability Proliferation of Clients Infrastructure: Proliferation of Platforms = ( server, OS, language ) Proliferation of Development Environments Increasing use of Collaborative Development Increasing use of Open source Increasing use of XML
	The PIA, an XML-based platform for Web Applications

<< 3 >> contents start	Challenges for Web Application Developers
	Which platform? Which development environment? How do programmers and content authors collaborate? How to maintain / customize applications?
	The PIA, an XML-based platform for Web Applications

<< 4 >> contents start	The Typical Web Application
	HTML documents for content, ``code'' for actions.
	The PIA, an XML-based platform for Web Applications

<< 5 >> contents start	PIA: an XML-Based Web Application Framework
	XML documents for both content and actions.
	The PIA, an XML-based platform for Web Applications

<< 6 >> contents start	A new design approach
	Uses a single XML-based language for : document markup (content) and data -- the ``conventional'' use for XML behavior -- very unconventional XML is a representation for parse trees The unique part is specifying behavior as well as style by assigning actions to tags. Can design an application-specific tag set Can process same document in multiple ways in effect, we've extended a stylesheet processor to interpret a complete scripting language. ... no !~+-*^%$#@ operators, no ( parentheses ) We also use document elements as data structures. what one might call document-oriented, as opposed to object-oriented, programming.
	The PIA, an XML-based platform for Web Applications

<< 7 >> contents start	Let's see how we develop a typical page
	Day of the week A Simple Form year: month: day: Tuesday
	The PIA, an XML-based platform for Web Applications

<< 8 >> contents start	Here's the XML for that page
	<h3>Day of the week</h3> <form action="&DOC:url;"> <heading>A Simple Form</heading> <numeric-input name="year" default="&year;"/> <numeric-input name="month" default="&month;"/> <numeric-input name="day" default="&day;"/> <form-submit name="day of week" /> <if-form-submitted> <weekday> <year>&FORM:year;</year> <month>&FORM:month;</month> <day>&FORM:day;</day> </weekday> </if-form-submitted> </form> parts look like plain HTML...
	The PIA, an XML-based platform for Web Applications

<< 9 >> contents start	Here's the XML for that page
	<h3>Day of the week</h3> <form action="&DOC:url;"> <heading>A Simple Form</heading> <numeric-input name="year" default="&year;"/> <numeric-input name="month" default="&month;"/> <numeric-input name="day" default="&day;"/> <form-submit name="day of week" /> <if-form-submitted> <weekday> <year>&FORM:year;</year> <month>&FORM:month;</month> <day>&FORM:day;</day> </weekday> </if-form-submitted> </form> other parts are application-specific...
	The PIA, an XML-based platform for Web Applications

<< 10 >> contents start	Here's the XML for that page
	<h3>Day of the week</h3> <form action="&DOC:url;"> <heading>A Simple Form</heading> <numeric-input name="year" default="&year;"/> <numeric-input name="month" default="&month;"/> <numeric-input name="day" default="&day;"/> <form-submit name="day of week" /> <if-form-submitted> <weekday> <year>&FORM:year;</year> <month>&FORM:month;</month> <day>&FORM:day;</day> </weekday> </if-form-submitted> </form> some tags perform processing...
	The PIA, an XML-based platform for Web Applications

<< 11 >> contents start	Processing is controlled by a tagset
	... that contains definitions for all the tags
	The PIA, an XML-based platform for Web Applications

<< 12 >> contents start	The tagset specifies what each tag does
	here's a typical tag definition <define element="if-form-submitted" syntax="quoted"> <doc> expand the content if responding to a form submission (query) </doc> <action> <if><get name="queryString"/> <then> <expand><get name="content"/> </expand> </then> </if> </action> </define> A tagset is simply another XML document
	The PIA, an XML-based platform for Web Applications

<< 13 >> contents start	Some tags are ``primitives''
	(A primitive is a tag defined by implementation code rather than defined in terms of XML.) <define element="if" class="ifHandler"> <doc> Expand the "then" sub-element if the condition is true (i.e. expands to something other than whitespace). </doc> </define> class attribute specifies the Java ``handler'' class for this primitive.
	The PIA, an XML-based platform for Web Applications

<< 14 >> contents start	The set of primitives is small
	<define> (<action> <value> <doc> ) <if> ( <test> <then> <else> ) <repeat> ( <for> <foreach> <while> <until> <first> <finally> ) <extract> ( <from> <child> <name> ... ) <make> / <do> / <namespace> / <properties> / <tagset> <get> / <set> / <let> / <bind> <include> / <write> / <status> / <connect> <numeric> / <logical> / <text> <protect> / <expand> / <hide> <sql> / <sign> / <sendmail> <date> / <url> About 30 primitive operations, comprising a complete language.
	The PIA, an XML-based platform for Web Applications

<< 15 >> contents start	Many domain-specific vocabularies
	For office forms <numeric-input> / <text-input> / <selection> / <signature> / <forms-pending> <notify> <numeric-input name="month" default="&month;" min="1" "max="12" /> For a datebook <weekday> / <calendar-row> / <show-month> / <show-one-day> / <get-appointments> <get-appointments day="&day;" month="&month;" year="&year;"
	The PIA, an XML-based platform for Web Applications

<< 16 >> contents start	Now let's look at data
	An application is more than just a single page We have to define the site structure http://risource.org/Calendar/month http://risource.org/Calendar/1999 ... and define which tag definitions to use for each document The PIA also does this using XML
	The PIA, an XML-based platform for Web Applications

<< 17 >> contents start	Site Structure may get complicated
	The PIA, an XML-based platform for Web Applications

<< 18 >> contents start	Site structure defined by XML
	Where to find the files <Container file="~/Calendar" virtual="/PIA/Apps/Calendar"> <Ext name="xh" type="text/html" tagset="Calendar-xhtml" /> <AGENT name="Calendar" time="0042"> <initialize> <user-message> Calendar initialized </user-message> </initialize> <daily-action> </AGENT> </Container>
	The PIA, an XML-based platform for Web Applications

<< 19 >> contents start	Site structure defined by XML
	how to map file types to tagsets <Container file="~/Calendar" virtual="~/PIA/Apps/Calendar"> <Ext name="xh" type="text/html" tagset="Calendar-xhtml"/> <AGENT name="Calendar" hour="00"> <initialize> <user-message> Calendar initialized </user-message> </initialize> <daily-action> </AGENT> </Container>
	The PIA, an XML-based platform for Web Applications

<< 20 >> contents start	Site structure defined by XML
	Agent runs at midnight <Container file="~/Calendar" virtual="~/PIA/Apps/Calendar"> <Ext name="xh" type="text/html" tagset="Calendar-xhtml" /> <AGENT name="Calendar" hour="00"> <initialize> <user-message> Calendar initialized </user-message> </initialize> <daily-action> </AGENT> </Container> Not using a DTD or PI's in the document.
	The PIA, an XML-based platform for Web Applications

<< 21 >> contents start	Tree-Structured Data Guarantees Well-formedness
	The PIA's internal representation is parse trees W3C's DOM (Document Object Model) -- widely available. All operations preserve structure Impossible to produce ill-formed output Most other platforms use strings: <h1><em>...</h1>(oops!) </em> Like the difference between ``GOTO's'' and structured programming. XML documents have a natural tree structure that is exactly what the author intended and that the PIA's operations understand.
	The PIA, an XML-based platform for Web Applications

<< 22 >> contents start	Platform-Neutral Processing
	Easy to merge two PIA-based applications ... or to mix with an existing application on any platform Standard API's for server-based platforms Apache module Java Servlet Cocoon Processor
	The PIA, an XML-based platform for Web Applications

<< 23 >> contents start	Portable Implementation
	Reference version written in Java for portability simple processing core Small number of primitive tag handlers Easy re-implemented in other languages (C port already in progress) Standard API's for non-server applications SAX (Simple API for XML) DOM (Document Object Model)
	The PIA, an XML-based platform for Web Applications

<< 24 >> contents start	Other PIA Components
	(You can read about these on the web site) Pluggable parsers and formatters HTML as well as XML Coexists well with other platforms Versatile site structure definition package Includes XML (WebDAV-ready) metadata Provides ``symbolic links'' or aliases Allows read-only directories with local overrides Hides file extensions (foo, not foo.html) Server / proxy with XML ``agents'' Useful for prototyping and testing Good platform for single user/small group applications Written in Java for portability Offline document processor
	The PIA, an XML-based platform for Web Applications

<< 25 >> contents start	Summary: Answering the Challenges
	Which platform? Whichever one you prefer: PIA applications are portable. Open Source processing engine eliminates dependence on proprietary technology can be integrated with any server engine or other XML applications How to collaborate? Shared editing of XML documents using domain-specific tags provided by programmers Integrating applications by merging documents Open source developer community at RiSource.org Which development environment? Whichever one makes sense for each collaborator. How to maintain / customize applications? Modify, extend the XML documents supported by mainstream editors and specialized clients
	The PIA, an XML-based platform for Web Applications

<< 26 >> contents start	Status and Resources
	Open source at RiSource.org/PIA/ Version 2.1 (first stable release) released 2000-2-29 Interactive demo/tutorial server at pia.rsv.ricoh.com/Tutorial/home Open-source collaboration on web applications Free collection of customizable apps C port in progress via SOURCEXCHANGE. Current status at sourcexchange.com/ProjectDetail?projectID=6
	The PIA, an XML-based platform for Web Applications

<< 27 >> contents start	Appendix: PIA Features
	Uses a single XML-based language for : document markup (content) data -- the ``conventional'' use for XML behavior -- very unconventional in a way, we are abusing a stylesheet language to make it interpret scripts Applications consist entirely of XML documents Makes applications portable Supports collaborative (open source) development Small, simple document-processing engine Versatile site-description package easily integrated into many platforms Open source code available on the net
	The PIA, an XML-based platform for Web Applications

<< 28 >> contents start	Comparison to PHP3
	and other platforms that embed code in web pages PIA PHP3 data representation parse trees strings can serve invalid pages no yes domain-specific tags yes no syntax XML C-like semantics macro expansions procedural separate actions from documents optional (design decision) no secure imported documents yes: restrict tags no
	The PIA, an XML-based platform for Web Applications

<< 29 >> contents start	Comparison to XSLT
	and other stylesheet-based publishing systems PIA XSLT complete scripting language yes no numeric expressions yes no text processing yes no variables yes no local substitutions yes no (XPointer is non- local) embed actions in documents optional (design decision) no supports legacy (HTML) docs yes no
	The PIA, an XML-based platform for Web Applications

<< 30 >> contents start	Table of Contents
	Outline Major Trends in Web Applications Challenges for Web Application Developers The Typical Web Application PIA: an XML-Based Web Application Framework A new design approach Let's see how we develop a typical page Here's the XML for that page Here's the XML for that page Here's the XML for that page Processing is controlled by a tagset The tagset specifies what each tag does Some tags are ``primitives'' The set of primitives is small Many domain-specific vocabularies Now let's look at data Site Structure may get complicated Site structure defined by XML Site structure defined by XML Site structure defined by XML Tree-Structured Data Guarantees Well-formedness Platform-Neutral Processing Portable Implementation Other PIA Components Summary: Answering the Challenges Status and Resources Appendix: PIA Features Comparison to PHP3 Comparison to XSLT
	The PIA, an XML-based platform for Web Applications