This file contains the 2ndt tutorial on XML, entitled "CML"

Its objectives are :
1) Familiarisation with CML, the Chemical Markup Language
2) The examination of a rather complex DTD
3) To understand why for such cases, the XML Shema is better
  than DTD.

The timing is purely indicative.
Total estimated timing : 12 minutes.

X. Gonze 2003-10-03

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Step 1. Examination of CML files.

Edit the three following files :
input1_CML.xml  input2_CML.xml  input3_CML.xml

XML is supposed to lead to self-descriptive files.
Question 1.1. Is it true ? What do you think these three files describe ?
(People familiarized with solid state crystallography will 
 likely have less difficulties than others). At least, how
 many atoms are there, and what are their type ?

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Step 2. Examination the DTD file.

Edit the corresponding DTD.
Note that the authors have defined a simplified "coreCML" language,
while the same DTD is presently active with the "fullCML" definitions.
Find the definition of the different elements of the XML file.
Note that there is no way to specify the number and type of allowed
values in the <stringArray builtin="elementType"> element, 
or in the <floatArray builtin="xFract">

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Step 3. A schema would be better. 

However, the available parsers do not implement yet completely
the XML Schemas recommendation.
Use your favourite browser to examine the status of Xerces,
a XML parser implemented in the APACHE XML project :
http://xml.apache.org

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Answer 1.1 . 
 input1_CML.xml is a elongated tetragonal cell,
 containing a slab of 10 molybdenum atoms, with BCC packing.
 input2_CML.xml is a cubic cell, containing 63 Carbon atoms,
 in diamond packing, with a vacancy at the origin.
 input3_CML.xml is an elongated cell, containing a slab of
 Silicon atoms, terminated by H and O atoms.

