GCA XML DevXML Lessons learned

David Orchard

Technical Architect

Pacific Development Centre

IntroductionPacific Development Centre

– New Lab in Vancouver Canada– Solutions/FOAK assets– Education, Government, Sports, Telecom, Banking

Technical architect on: IBM Student Server

– University student self-service web Asset– Access to all silo-based functions

• registration, tuition, admission, grades, …

– Prototype May 98– Ver 1.0 Asset shipped Oct 98– Ver 2.0 Live at University of Minnesota– One of first IBM web sites/app using XML

Some modest RequirementsPeopleSoft Student Admin 7.0

– Running on Sun E10000 box– Oracle– has >5000 tables– Access by PS GUI and our app

Integrate with University’s X.500Performance:

– 100 concurrent threads/requests– hundreds of requests/second.– Peak registration week has 60 registrations/minute

Updates through Win32 based api– registration actually done by 30 second COBOL job!

Reads through ODBC

Solution architectureWeb App front end on IBM 3 node 16 cpu SP2

– IBM WebSphere 2.0 Standard– WebSphere performance pack for load-balancing

24 Windows NT boxes for PS API– Connect via RMI

Developed using Visual Age, FrontPage IBM Java 1.6 VM, XML4J Parser

Design DecisionsDecided on XML in Nov 97EJB Style persistence

– No Containers or transactions

Servlets then JSPsPS & DB ConnectorRoles-based UI

Declarative/XML usages:1. Runtime generation of HTML from Java (XML)2. Compile-time generation of Java (XML)3. Runtime specification of Java Objects and

Templates (.SHTML)Rejected as transfer over HTTP between nodes

– RMI used

Note: All 3 forms use Java at run-time, NO run-time XML

Runtime Java->HTMLVia XML+XSL

– Java object->XML, +XSL->HTML– Wrote Java code to convert Java to XML using DOM– Thrown out due to XSL tech + performance difficulties

Via HTML Template– IBM internal template programming language (TPL)

• Applies XML template to Java Object

• Produces any textual output

– Java object + XML-based HTML template -> HTML

Note: Java Server Pages (JSP) can do first 2– JSP not available at the time ( Last year )– I still like TPL better

Note 2: JSP/XSL different architectures

IBM Template Processing Language<template>

The business object description is: $description$

<scope PROPERTY="career">

The career code is: $code$

<table>

<repeat PROPERTYARRAY="terms">

<tr>

<td>$code$</td>

<td>$description$</td>

</tr>

</repeat>

</table>

</scope>

</template>

EJB-ish object defn. (YAEJBML)

Data Object definition, EJB Template (XML)TPL basedGenerates Home, Key, Interface, Data Object,

Business ObjectOur EJB-ish beans don’t have containers or

descriptors

YAEJBML sample

<?xml version="1.0"?>

<!DOCTYPE DOlist SYSTEM "../../DTD/DO.dtd">

<DOlist>

<DO name="StudentEnrollment" package="com.ibm.studentserver.enroll">

<property name="emplid" key="true"/>

<property name="classNumber" key="true"/>

<property name="enrollStatus" />

</DO>

</DOlist>

XML ViewsUsed Lazy initialization of relationshipsPerformance was awful!Created SQL Views with matching XML ViewsBinds SQL Views to YAEJBML elementsNew findBy method on Home

– follows view specification

Some restrictions:– Result Set Columns must be grouped by Bean– No circular references

Declarative Non-XML usageCreated Web Object Builder (WOB)Parameters to WOB Servlet

– Business Object, Keys, FindBy Method, Template

<SERVLET NAME="WebObjectBuilder" CODE="com.ibm.whistler.WebObjectBuilder">

<PARAM NAME="TEMPLATE" VALUE="com.ibm.whistler.studentserver.currentenrollment.CourseInformation_CurrentEnrollmentsViewImpl">

<PARAM NAME="BUSINESS_OBJECT" VALUE="com.ibm.whistler.studentserver.currentenrollment.CurrentEnrollmentsView">

<PARAM NAME="HOME_METHOD" VALUE="findBy">

<PARAM NAME="KEY" VALUE="EMPL_ID">

<PARAM NAME="KEY" VALUE="INSTITUTION">

</SERVLET>

Declarative mechanism for:BO Home.findByMethod(Keys from POST or

session data )Lock web sessionset web session on BOexecute method specified or commit() render according to templateget web session data from BOput into web sessionunlock web session

Declarative everywhere:PeopleSoft or RDB binding to Java class (DO) in

XMLViews binding in XMLTemplate for Java object to HTML in XML

– Originally XSL then IBM template tool

HTML/JSP page specifying Java Object and Template to render

VIP: Everything can be declarative– Assumes no behavior in Java Object– But: can add behavior betwixt presentation and DO

+ve Design lessonsDeclarative means reuse at design/compile time!

– View optimizer would have been much harder if EJB code

Declarative means easily regenerate code– Not as many options for tracing/logging/debugging– Much easier to create hundreds of DOs than VAJ– Complete control over behavior and interface

Declarative means easy to adapt– IMHO, adaptability is a crucial success factor– refactoring classes meant text search and replace

• GUI developers didn’t need VAJ

Declarative means easy to author– Data Objects, Object templates, Web templates

-ve Lessons LearnedMyths:

– XML will replace Java programming – XML always means presentation independence– Java + DOM are sufficient/”perfect together”– XSL is easy and will become ubiquitous– Model Data correctly for interchange

Observations about XML and Transforms

Myth: Procedures in XMLTried in 2 places

– HTML Template– DO templates

End up creating declarative constructs for:– parameters, data types, expressions, loop constructs,

variable scoping, subclassing/extension

Can became convoluted– TPL, XSL suffers from this

Can’t author/debug like JavaSuggestion: Declarative for pattern matching

– sed/awk/perl/xsl– Better Java text templating would have solved problem

Myth: Presentation IndependenceSoo many RFPs with the XML+XSL to any client

– Especially XML to IVR + Palmtop + browser + other business

Works in many cases, usually document focused– Similar styles of documentation - print + web pages– Rebranding of content - stories to branded web sites

Interactive web sites are a different storyMany issues from XML to client:

– Navigation, Input Data validation, Output Formatting, Amount/ordering of content, Scrolling in content

Process becomes multi-step– Dispatcher queries for content, then format

Suggestion: XML best chance at re-use

Myth: Java/XML “perfect together”Common B2B, B2C Use Case:

– Take lots of EJBs and convert to XML– Condition: read-only classes and DTDs

Either:– Write procedural code using DOM to serialize– Use reflection-based Conversion

Usually use DOM– Poor performance in current implementations

Transfer strongly typed XML tree to Java tree– ie public class student -> <student></student>

XML/Java issues Inheritance

– Java has, XML doesn’t– Contain/embed/link to the parent?– Implements, extends?

References– Java has handles, XML has Linkss

Typing– Java primitives to strings and back

Built-in types + Java classes– Array/Vector/List/Hashtable become ??– String value become attribute or entity

XML Pis and Comments

Java/XML ideasSerialization Proposal:

– XML binding for Java<-->XML aka YAEJBML– NOT the focus of the Sun Java/XML data binding JSR

Compile XSLT to Java for performancePerl/SAX pattern/entity matching in Java Interface between XSLT and Java

– call XSLT from JSP– call Java from XSLT

– BUT: still problems of type conversion

Java based template string and streams– MessageFormat is awful, poor child of sprintf

– generalization of JSP

– Perl, others have

IMHO, only “perfect” because java xml parsers

Myth: XSLT solves presentationXSLT is declarative programming language

– XSL has all the constructs of a programming language• Procedures, parameters, variables, VM (DOM)

– Difficult to author and debug• ie, creating a Form with CSS, JavaScript, nested tables

• Course list table with radio buttons select course and required subcomponents

XSLT needs usability performance/scalability improvements– Serialize Java tree into DOM tree currently

Solution: Know when to use XSL vs JSP

Myth: Model Data “Correctly”Same “Universal Model” myth heard with rdb

and Java– Same modeling problems exist in XML

Example: When is a person a student?– Finance dept: When fees charged– Registrar:Accepted to University– Department: Enrolled in any course– Instructor: Enrolled in course with grade– Student society: Paid student fee

Do you create a student entity?Solution: Don’t be deluded into “correct” model

thinking

ObservationsXML everywhere means transforms are key

– Need to chain multiple transforms together• Different sources/sinks of transform data

– Transforms are behavior• Death of O-O?

• Where does Java fit?

Watch for much confusion in market on– JSP+ EJB on DB versus XSLT+XML on DB

XML Schema AnnouncementPreview of new XML4J functionality

– binary only, 90 day license, to be updated frequently– feedback to XML4J@us.ibm.com

Supports subset of 6 May 1999 Schema Working Draft– subset corresponds to DTD functionality - no

datatypes– track the whole Schema spec– read and validate documents using either DTDs or

schemas– convert DTDs to schemas and schemas to DTDs

access to DTD and Schema via a DOM extension

SummaryXML widely usable for defining Data

– Debatable use for defining behavior/procedures

Combined with code generation– Adaptable software– Easy to author– End2End functionality without Java

Can be part of large performance & scalability systems– Student Server

Proven Universal Data LanguageNeeds work, watch out for hype

– tooling, maturity, Java integration

Pretty Good for a toddler!