NYCPHP Meetup

[charles at softwareprototypes.com]

XML (eXtensible Markup Language) is a way of tagging a stream of data.

DTDs (Document Tag Definitions, usually in a seperate document,) are
required to that system A and system B can agree on the semiotics
(the semantics and c0ontextual dependencies,) of the tags and thus
exchange information.

XML is a format for expressing data contained in a file or data base.
It is NOT a database.

As for rendering, use XSLT (eXtensible Stylesheet Language
Transformation) because that what it does. Expresses XML streams into
something renderable by transforming these into HTML.

There si no decision to be made. They are used in entirely seperate
areas.

A database (MySQL, PostGreSQL, DB2, Oracle, etc,) stores data (with
varying success and apply varying degrees of validation and
relational integrity checking.) It can also receive data and transmit
data as an XML stream. (You don't want to deal with a database engine
that doesn't.)

XML is a human readable means of transmitting the data to/from a
database engine, a busines logic layer, a transation procesing layer
or a interaction layer (GUI or merely CUA compliant inter-system
interface.) 

Think of XML as applying meaning to TCP/IP by wrappering it just as
HTML does to web page content and you'd be closer to its intent.

-Charles-A.