What exactly does xml do?

XML is a bridge between humans and computers that can be easily expanded in order to make computers efficient in manipulating even large or very large databases encoded with this method.
More explicitely, it is a significant effort to create a universal language that Can encode data and structures of data Is easily readable and writable with most programming languages due to the well known and documented specifications and the availability of interface libraries for most languages, if not all
Using a part of the standard, the Document type definition (DTD) it is possible to impose restrictive
rules on the data to be encoded
There are other standards to achieve similar purposes,
for instance JSON that to my knowledge lacks a
standardized system like DTD, that has similar
features but is somewhat simpler to implement in a
library.
I can hardly enumerate all the possible applications I
have seen leveraging its power, just a some
examples:
Configuration files: software applications often
need some form of configuration to adapt them to
the customer’s needs. XML is perfect for this as it is
easily understandable even by not skilled users,
and can be read by an application with small
overhead.
Serialization and data transmission: if I have two
different applications or tasks running on different
computers and connected through the net,
exchanging data encoded in XML is straightforward.
Chances are that the last order you issued to an e-
commerce site was sent encoded either in JSON or
in XML
Languages: many languages can be encoded in
XML. Recently I had to use a visual language to
instruct a robot to move. Movements could be very
complicated, depending on many sensors and
measured conditions. The way to instruct that robot
how to move was a visual language, i.e. a system
that permits to create a program not with words
but with symbols on screen, that was encoded in
XML before execution.
So the visual front end gave all the programming
primitives to the user, but the visual program was
encoded in XML for the robot to execute it.
General programming: if you program in languages
like Java or C# or… you name it, the logical
relationships between the various components, for
instance the solution and project file in Visual
Studio, is an XML encoded file that can be edited
with visual widgets but, for many possible
purposes, can be edited with an editor or with
other programs.
It is used in many applications of the concept of
NoSql database (
XML database) that is a flexible
alternative to more traditional table-based sql
databases.

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