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 JXML, Inc. 2000
All Rights Reserved
January 18, 2000
XML
Data
The JXML
Vision
Bill la Forge, CTO
JXML, Inc.
www.jxml.com
[email protected]
 JXML, Inc. 2000
All Rights Reserved
Overview
1. Historical View
2. What is XML?
3. Protocol Issues
 JXML, Inc. 2000
All Rights Reserved
1. Historical View





1960’s: Data Centric
1970’s: Process Centric
1980’s: Object Oriented
1990’s: Component Based
2000’s: XML?
 JXML, Inc. 2000
All Rights Reserved
Data was our First Focus
•Record Layouts
•Printer Layouts
•System Flow Charts
•Decision Tables
60’s
Data
Batch Jobs were a Series
of small Programs
 JXML, Inc. 2000
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Then we Focused on Logic
•GOTO-Less Programming
•Structured Programming
•Top-Down Design
60’s
Data
70’s
Logic
Programs Became
Very Large
 JXML, Inc. 2000
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Object Oriented Programming
Focused on Runtime Behavior
•Common Terms for
Analysis and Design
•Tightly Coupled Code
60’s
Data
70’s
Logic
Code Reuse was the Holy Grail,
Rarely Achieved
80’s
OO
 JXML, Inc. 2000
All Rights Reserved
Component Programming
Shifted the Focus to Interfaces
•Code Reuse
•IDE-Based Composition
•Limited Acceptance
60’s
Data
70’s
Logic
90’s
Comp
Serialization Tied to Code
80’s
OO
 JXML, Inc. 2000
All Rights Reserved
XML Returns the Focus to Data
•XML Wrappers for Incompatible Systems
•Industry-Specific Markup Languages
•XML for Persistent Data and Composition
00’s
XML
70’s
Logic
90’s
Comp
XML Enables Middleware
for Application-Specific Data
80’s
OO
 JXML, Inc. 2000
All Rights Reserved
2. What is XML?




Just Tagged Text
DTDs & Schema
Namespaces & Schema
Recommended Practice
 JXML, Inc. 2000
All Rights Reserved
Just Tagged Text
<document>
<hasText>123</hasText>
<hasElements q=“76”>
<hasAttributes
x=“1” y=“23”/>
</hasElements>
</document>
•An XML file is called a
Document
•Documents have one
top-level Element
•Elements have Matched
Start & End Tags, or a
Combined Tag
•The Content Between
the Tags can be Text
or Elements
•Attributes are
Name/Value Pairs
within the Start or
Combined Tag
 JXML, Inc. 2000
All Rights Reserved
DTDs and Schema
DTDs



Define Structure,
but Not Content
Author can
Override a DTD
within a Document
Best Used for
Interactively
Authoring an XML
Document
Schema



Define Structure
And Data Content
Author can Not
Override a
Schema within a
Document
Best Used to
Validate Program
Input
 JXML, Inc. 2000
All Rights Reserved
Namespaces & Schema




Namespaces enable the use of more
than one Schema with a Document
Each Namespace has a unique URL
Each Schema defines a Namespace
(More than one kind of Schema can be
used to define the same Namespace)
Namespaces Enable Modular &
Reusable Schema
 JXML, Inc. 2000
All Rights Reserved
Recommended Practice

Do Not mix Text and Elements at the Same Level
<e1>text1<e2/><e1>

Avoid Attributes on Elements with Text Content
<ele v1=“abc”>some text</ele>

Text is Preferred over Attributes

Difficult to Format Attributes for Display
 JXML, Inc. 2000
All Rights Reserved
3. Protocol Issues



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
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Document-Based Protocols
Packaging
Opaque Data
Digital Signatures
Serialization—The Wrong Focus
Beyond RPC
 JXML, Inc. 2000
All Rights Reserved
Document-Based Protocols


Emphasis on Message
Format
Separation of Validation
and Processing
 JXML, Inc. 2000
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Packaging
Routing
Signature
Transactional
Application
 JXML, Inc. 2000
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Opaque Data

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Protocol Stacks, N-Tier Applications, and Data
Mining must all deal with information outside of
their Domain.
It is sufficient that a Document is well-formed.
Validation only Selected Elements Increases the
Robustness of these Processes
 JXML, Inc. 2000
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XML Digital Signatures

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End-to-End Non-Repudiation
Entire Documents or Individual
Elements can be signed
Signature can be in the Same or
Separate Document
Changes to Whitespace does Not
Invalidate an XML Digital
Signatures
 JXML, Inc. 2000
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Serialization
—The Wrong Focus


Focused on Objects, Not Data
Objects->XML->Objects
XML produced is either a specific XML
Markup Language or is not conformant
to any Markup Language
BeanML (IBM) is one-way, but fast
XML->Objects
 Archiver (Sun) is roundtrip and compact,
but slow
 SOAP (Microsoft) is language-neutral,
but non-conformant

 JXML, Inc. 2000
All Rights Reserved
Beyond RPC
XML does not lend itself to a direct
implementation of RPC, per say, as such efforts
lean to the use of Serialization.
Consider instead an XML Messaging System,
where the Document as a Whole specifies the
Intent of the Requestor.
The key here is to stay Focused on the Data
being passed, rather than trying to Model an
RPC call.