(I was hoping it wouldn't come to this)

a tag based meta-language for creating other languages. The use of a DTD or Schema
allows derived languages to be defined. The DTD or Schema is used to define the TAGs
that are permitted in the sub-language. XHTML is a classic implementation of an XML
derive language. What is so great about XHTML - it can be modified (for different
display devices) in flight, by XSL (another XML derived technology).

XML allows the creation of self describing data. Self describing data offers significant
benefit in being used to pass documents and messages among otherwise incompatible
systems.

XML Tags allow XML <ELEMENTS> to be better identified when a document is
searched for its content. This is near to impossible with EDI documents in their
transmitted form as it is with messages passed between CORBA, DCOM & RMI.

The concept (like a cargo container) is incredibly simple but its simplicity doesn't
mean the impact will not be dramatic (as was containerization). XML is the same.

What is driving 'needs' for XML. It is the need for a simple but powerful mechanisim
that can be integrated into existing systems (EAI & Legacy) but can also support
entirely new concepts like Web Services, ebXML. XML Query etc: etc: etc: etc:.

XML is human readable but XML derivative standards support the ability to handle
encryption. XML can support encryption of <ELEMENTS> and it is entirely
possible for each <ELEMENT> to use a different encryption approach. So, one
might ask, what is the big about being human readable ? - this ability opens the
pandora's box of discovery !. Discovery of content, one of the greatest inhibitors in
analysing and exploiting data in information systems. Yes, there is a price, (lack
of data compression) but already hardware vendors are developing intelligent
routers capable of compressing XML in transit without losing its 'visibility'.

XML has derivative standards that support non-repudiation. An essential
ingredient for electronic document exchange.

XML has a concept (Global DOCID) that supports a unique document ID for
each any every document that chooses to employ it. This offers significant
benefits in managing XML based documents that travel globally. And that
need to be traced to their origins.

Web Services is a concept derived from XML and thus harnesses the
significant benefits already recognised in the technology. Web Services
allows the concept of 'COLLABORATIVE COMPUTING' which is the next logical
step in the evolution of computing use. In essence it is computung that spans
computers and is technology agnostic. Web Services does this. CORBA DCOM
& RMI (as methods of linking computing) arent & can't.

Web Services can do one other extremely important trick that CORBA, DCOM &
RMI can't. Becaues of XML and WSDL, They can be bound to in real time. The
other middleware technologies have to be bound together at compile time (this
seems to be so lost on many people who criticze the Web Service concept).
This 'trick' gives Web Services its magic and like XML human readability, opens
a pandora's box of potential that proprietary & non web scalable technologies
(CORBA etc:) can never rise to.

Web Services can be said to be the forunner of a 'plug and play' solutions
capability. This is where the benefits can be passed to business. If businesses
can create solutions by real-time & dynamic binding of services using business
flow languages then the world of business & IT has move substantially forward.

IN DEFENCE of CORBA etc:
But there are applications where proprietary technologies like CORBA etc: offer
value that Web Services can't (yet).

Some today say the the next big Wave will be 'GRID' computing and for that to
make sense, Web Services need to proceed as it will, down its evolutionary path.
No doubt some people have no view whatsoever of computer evolution just as
some shippers might never have grasped the benefits of containerization.

Brings to mind the famous British story of when King Canute (11th century)
sought to teach some of his aides how not even the King of Scandanavia and
England could command the tide to turn back. Darwin taught us some
powerful principles in his oragins of the species.

XML standards are driven by the W3C (WWW Consortium)
[link|http://www.w3c.org/|W3c web site]
Its a damned shame the above web site is so academic and boring if it
wasn't them maybe many more people would read the details.

W3C has defined a \ufffdfamily\ufffd of XML related technologies ... (just a few here)
XML, XHTML, DTD, XML Schema,
XML Query, XSL, XSLT, XML Path,
XLL, etc:, etc:, etc:.

XSL is a topic in its own right.

All and more can be read at the link provided.

Cheers - Doug Marker

#1 added more detail

Actually the whole box & dice is very far reaching. If one looks at the bulk of standards being defined at W3C - most are now based on some XML derivative. I have hardly touched on the derived languages that have already been designed and the others in the 'mill'.

There are XML derived languages for video streaming, voice data, image data etc: etc: (I don't know exactly what they do but someone saw fit to create them.

Many of these 'languages' (which are nothing more that a set of TAGs & rules for their appearance in the language, and are defined in a schema) are being defined by industry groups seeking to simplify the exchange of data between partners - this is most noticable in the Supply-Chain-Management industry which was of course the industry the drove & benefitted from containerization.

XML & Web Services specifically attempt to overcome the problems of EDI in an elegant manner that can be readily picked up by bulk of SMEs (small to medium enterprises) that today can't afford the complexity of EDI but must do business with the top 5-1-% who cannot run their business without EDI. (it pays to remember the Govts ran fastest ahd hardest with EDI & demand EDI protocols for government provisioning. This applies as much to US as to EU.

One other bit of 'magic' that was built into XML is that of language version control. This is akin to the DLL Hell on windows.
The issue is - ver 1.0 of a language appears (say it is dialect used for ordering auto-spare parts). Anyway along comes an upgrade - how does it get implemented without screwing all the apps that have linked to service providers delivering ver 1.0 formatted data. The XML approach
is that the DTD or Schema (actually the DTD is doomed to extinction as it is a patheticly simplistic & non-XML compliant mechanism that has been eclipsed by the XML Schema). Any the Schema gets published so resides at one primary location (which is likely to be replicated) and all users of a document that rely on that Schema include a link to that schema (ver 1.0) in their Documents.

To move to ver 2.0 - the schema creator only needs to create a new schema that contains the differences & link back to the original schma from the new one. This way we have two schemas published ver 1.0 & ver 2.0 & 2 only contains the changes from 1 thus any software that processes ver 2 documents will always validate against the ver 2 schema whilst any documents created with ver 1 can still refer to the version 1 schema rules.

This is a bit like object oriented inheritance. Any new schema inherits the properties of its parent but can overide some definitions and add new ones but all the other stuff is as in the previos version.

So XML offers an elegant and simple and effective version capability. This is a critical requirement for Web Services as it means a services provider can run the old and new service alongside each other. It is up to the servise requestors to determis which version or format that want to use. This means that changes don't have to break applications that are built on older versions of services.

Cheers

Doug Marker

I have just obtained an excellent article from Harvard Business review that describes in a good way
the impact of XML / Web Services. When I can get the soft copy I will post a link or an extract.

It puts the impact this way

"End of proprietary computing as we know it"

As regard containerization, there are many comparisons & aspects to an anology. I have been working
on bring these together into a presentation.

Cheers

Doug