xml data bill la forge, cto jxml, inc. [email protected] jxml, inc. 2000 all rights reserved...

XMLData

Bill la Forge, CTO

JXML, Inc.

www.jxml.com

[email protected]

JXML, Inc. 2000All Rights Reserved January 18, 2000

The JXMLVision

Overview

1. Historical View2. What is XML?3. Protocol Issues

JXML, Inc. 2000All Rights Reserved

1. Historical View

1960’s: Data Centric 1970’s: Process Centric 1980’s: Object Oriented 1990’s: Component Based 2000’s: XML?


Data was our First Focus

60’sData

•Record Layouts•Printer Layouts•System Flow Charts•Decision Tables

Batch Jobs were a Seriesof small Programs


60’sData

70’sLogi

c

Then we Focused on Logic

•GOTO-Less Programming•Structured Programming•Top-Down Design

Programs Became Very Large


60’sData

80’s

OO

70’sLogi

c

•Common Terms for Analysis and Design•Tightly Coupled Code

Object Oriented ProgrammingFocused on Runtime Behavior

Code Reuse was the Holy Grail, Rarely Achieved


60’sData

90’sComp

70’sLogi

c

80’s

OO

Component Programming Shifted the Focus to Interfaces

Serialization Tied to Code

•Code Reuse•IDE-Based Composition•Limited Acceptance


00’sXML

70’sLogi

c

80’s

OO

90’sComp

•XML Wrappers for Incompatible Systems•Industry-Specific Markup Languages•XML for Persistent Data and Composition

XML Returns the Focus to Data

XML Enables Middleware for Application-Specific Data


2. What is XML?

Just Tagged Text DTDs & Schema Namespaces & Schema Recommended Practice


Just Tagged Text

•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

<document> <hasText>123</hasText> <hasElements q=“76”> <hasAttributes x=“1” y=“23”/> </hasElements></document>


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


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

Namespaces & Schema


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

Recommended Practice


3. Protocol Issues

Document-Based Protocols Packaging Opaque Data Digital Signatures Serialization—The Wrong Focus Beyond RPC


Document-Based Protocols

Emphasis on Message Format

Separation of Validation and Processing


Packaging

Routing

Signature

Transactional

Application


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

Opaque Data


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

XML Digital Signatures


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


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.
