XML Data Storage

=XML for Data storage= 
==XML== 
XML is a flexible, convenient, way of storing data, once you understand how.
Programs typically evolve thru several versions. This often results in different data items being stored. This has meant careful tracking of data version vs program versions, as programs could not correctly read data from the wrong data version.
XML is a flexible as names are stored with the data. Names which are understood can be read, while others are ignored. The downside is that missing variables may require defaults.
XML is a very convenient to use. The rules are quite simple.
XML consists of elements:

<name> text </name>

Every opening <name> is paired with a closing </name).
Names can be almost anything but are case sensitive.
Elements can be wholly contained within other elements. <Name1> <xyz> </xyz> </Name1>
Elements cannot overlap. <Name1> <xyz> </Name1> </xyz>

for more details visit: http://www.w3schools.com/xml/xml_syntax.asp

==Saving Data== 
The following example shows only the code to open and write a file.
[[code format="lb"]]
sub FileSaveAs
 filedialog "Save file", FilePath$+"*.Sudoku", FullName$
 call GetFileName$
 if FileName$="" then notice "No file chosen!": end
 call FileSave
end sub

sub FileSave
 open FullName$ for output as #File
 FileOpen = True
 #File "<XML>"
 #File "<!-- "; Date$();" "; Time$();" ";FullName$;" -->" 'XML comment
 #File " <Sudoku>"
 call SaveOptions
 call SaveCells
 #File " </Sudoku>"
 #File "</XML>"
 close #File
 FileOpen = False
 notice "Puzzle Saved ";chr$(13);_
 "File Name ";FileName$;chr$(13);_
 "at ";FilePath$
end sub

sub SaveCells
 for row = 1 to 9: for col = 1 to 9
 if CellValue(row,col) <> 0 then
 call SaveOneCell row, col, CellValue(row,col), CellStage(row,col)
 end if
 next col: next row
end sub

sub SaveOneCell row,col,value,stage
 #File " <Cell>";
 #File "<Row> ";row;
 #File " </Row>";
 #File "<Col> ";col;
 #File " </Col>";
 #File "<Value> ";value;
 #File " </Value>";
 if stage <> 1 then
 #File "<Stage> ";right$(" ";str$(stage),2);
 #File " </Stage>";
 else
 #File " ";
 end if
 #File "</Cell>"
end sub

sub SaveOptions
 #File " <Size> ";9;" </Size>"
 #File " <Diagonal>";
 if DiagActive then #File " On "; else #File " Off ";
 #File "</Diagonal>"
 #File " <Possible>";
 if PossibleShow then #File " On "; else #File " Off ";
 #File "</Possible>"
 #File " <Reduce> ";
 if ReduceActive then #File " On "; else #File " Off ";
 #File "</Reduce>"
end sub

sub GetFileName$
 for pos = len(FullName$) to 1 step -1
 if mid$(FullName$, pos, 1) = "\" then exit for
 next pos
 FileName$ = mid$(FullName$,pos+1)
 FilePath$ = left$(FullName$,pos)
end sub
[[code]]
==Example data file:==
[[code]]
<XML>
<!-- Mar 12, 2014 10:56:25 C:\Data\Sudoku\3.40.88.Sudoku -->
 <Sudoku>
 <Size> 9 </Size>
 <Diagonal> Off </Diagonal>
 <Possible> Off </Possible>
 <Reduce> Off </Reduce>
 <Cell><Row> 1 </Row><Col> 1 </Col><Value> 7 </Value> </Cell>
 <Cell><Row> 1 </Row><Col> 7 </Col><Value> 9 </Value> </Cell>
 <Cell><Row> 1 </Row><Col> 8 </Col><Value> 3 </Value> </Cell>
 <Cell><Row> 2 </Row><Col> 4 </Col><Value> 6 </Value> </Cell>
 <Cell><Row> 2 </Row><Col> 5 </Col><Value> 4 </Value> </Cell>
 <Cell><Row> 2 </Row><Col> 6 </Col><Value> 7 </Value><Stage> 2 </Stage></Cell>
 <Cell><Row> 3 </Row><Col> 1 </Col><Value> 1 </Value> </Cell>
 <Cell><Row> 3 </Row><Col> 9 </Col><Value> 7 </Value> </Cell>
 <Cell><Row> 4 </Row><Col> 2 </Col><Value> 6 </Value> </Cell>
 <Cell><Row> 4 </Row><Col> 3 </Col><Value> 8 </Value> </Cell>
 <Cell><Row> 4 </Row><Col> 4 </Col><Value> 5 </Value> </Cell>
 <Cell><Row> 4 </Row><Col> 7 </Col><Value> 7 </Value> </Cell>
 <Cell><Row> 5 </Row><Col> 4 </Col><Value> 3 </Value> </Cell>
 <Cell><Row> 5 </Row><Col> 5 </Col><Value> 8 </Value><Stage> 2 </Stage></Cell>
 <Cell><Row> 5 </Row><Col> 6 </Col><Value> 2 </Value> </Cell>
 <Cell><Row> 6 </Row><Col> 3 </Col><Value> 2 </Value> </Cell>
 <Cell><Row> 6 </Row><Col> 6 </Col><Value> 6 </Value> </Cell>
 <Cell><Row> 6 </Row><Col> 7 </Col><Value> 8 </Value> </Cell>
 <Cell><Row> 6 </Row><Col> 8 </Col><Value> 5 </Value> </Cell>
 <Cell><Row> 7 </Row><Col> 1 </Col><Value> 9 </Value> </Cell>
 <Cell><Row> 7 </Row><Col> 5 </Col><Value> 6 </Value><Stage> 2 </Stage></Cell>
 <Cell><Row> 7 </Row><Col> 9 </Col><Value> 1 </Value> </Cell>
 <Cell><Row> 8 </Row><Col> 4 </Col><Value> 1 </Value><Stage> 2 </Stage></Cell>
 <Cell><Row> 8 </Row><Col> 5 </Col><Value> 2 </Value> </Cell>
 <Cell><Row> 8 </Row><Col> 6 </Col><Value> 3 </Value> </Cell>
 <Cell><Row> 9 </Row><Col> 2 </Col><Value> 4 </Value> </Cell>
 <Cell><Row> 9 </Row><Col> 3 </Col><Value> 1 </Value> </Cell>
 </Sudoku>
</XML>
[[code]]