GCA XML Dev XML Lessons learned

GCA XML DevXML Lessons learned David Orchard Technical Architect Pacific Development Centre

Introduction • Pacific 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 Requirements • PeopleSoft 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.500 • Performance: • 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 architecture • Web 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 Decisions • Decided on XML in Nov 97 • EJB Style persistence • No Containers or transactions • Servlets then JSPs • PS & DB Connector • Roles-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->HTML • Via 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 based • Generates Home, Key, Interface, Data Object, Business Object • Our 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 Views • Used Lazy initialization of relationships • Performance was awful! • Created SQL Views with matching XML Views • Binds SQL Views to YAEJBML elements • New findBy method on Home • follows view specification • Some restrictions: • Result Set Columns must be grouped by Bean • No circular references

Declarative Non-XML usage • Created 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 session • set web session on BO • execute method specified or commit() • render according to template • get web session data from BO • put into web session • unlock web session

Declarative everywhere: • PeopleSoft or RDB binding to Java class (DO) in XML • Views binding in XML • Template 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 lessons • Declarative 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 Learned • Myths: • 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 XML • Tried 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 Java • Suggestion: Declarative for pattern matching • sed/awk/perl/xsl • Better Java text templating would have solved problem

Myth: Presentation Independence • Soo 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 story • Many 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 ideas • Serialization Proposal: • XML binding for Java<-->XML aka YAEJBML • NOT the focus of the Sun Java/XML data binding JSR • Compile XSLT to Java for performance • Perl/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 presentation • XSLT 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

Observations • XML 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 Announcement • Preview 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

Summary • XML 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 oflarge performance & scalability systems • Student Server • Proven Universal Data Language • Needs work, watch out for hype • tooling, maturity, Java integration Pretty Good for a toddler!

GCA XML Dev XML Lessons learned