Core SuperMemo XML for exchange of text questions, answers and learning data

This is a simplified core implementation for basic data exchange between SuperMemo for Windows, SuperMemo for Pocket PC, SuperMemo for Palm Pilot, On-line SuperMemo, SuperMemo Library, and other platforms currently in development.

Here is an intuitive example (actual files exported by SuperMemo for Windows can be found here):

<?xml version="1.0" standalone="yes"?>
<?xml-stylesheet type="text/xsl" href="http://supermemo.com/archive/beta/tmp/xml/supermemo.xsl"?>
<SuperMemoCollection>
  <Count>1329</Count>
  <SuperMemoElement>
      <ID>78345</ID>
      <Content>
         <Question>hist: The city of Carthage, located in what is now Tunisia, had been founded in [...] by the Phoenicians</Question>
         <Answer>814 BC</Answer>
      </Content>
    <LearningData>
       <Interval>323</Interval>
       <Repetitions>3</Repetitions>
       <Lapses>1</Lapses> 
       <LastRepetition>23.11.2000</LastRepetition>
       <AFactor>1.456</AFactor> 
       <UFactor>1.121</UFactor>
    </LearningData>
             <SuperMemoElement>
                    <ID>78346</ID>
                          <Content>
                               ...
                          </Content>
             </SuperMemoElement>
  </SuperMemoElement>
</SuperMemoCollection>

• SuperMemoCollection - root element holding nestable SuperMemoElement's
• SuperMemoElement - single element (item, topic or task) composed of ID, Content (Question and Answer), and LearningData. SuperMemoElement can nest other SuperMemoElement's. The nesting structure can be used to reflect the knowledge tree
• Count (optional but recommended) - number of elements in the collection (on import, disregard this value if, in error, it differs from the actual number)
• ID - element ID relative to a given collection (the last segment of the global element ID)
• Question - first question component with default markup-encoded HTML formatting; alternative to Component with Text subset type and DisplayTime attributes set to Question
• Answer - first answer component; alternative to Component with Text subset type and DisplayTime attributes set to Answer
• AFactor - difficulty attribute that must be computed from E-Factors in non-Windows SuperMemos
• UFactor - quotient of the recent interval increase (in algorithms based on E-Factors: UFactor is 1 for Repetitions=1 and equal to E-Factor otherwise)

Procedures

Heuristic conversion of E-Factors to A-Factors (subject to change):

const
minAF=1.2;
maxAF=6.9;
minEF=1.3;
maxEF=3.3;

function EFactor2AFactor(EF:real):real;
begin
  Result:=minAF+(EF-minEF)/(maxEF-minEF)*(maxAF-minAF);
  if Result>maxAF then Result:=maxAF;
  if Result<minAF then Result:=minAF;
end;

function AFactor2EFactor(AF:real):real;
begin
  Result:=minEF+(AF-minAF)/(maxAF-minAF)*(maxEF-minEF);
  if Result>maxEF then Result:=maxEF;
  if Result<minEF then Result:=minEF;
end;

function EFactor2UFactor(EF:real;Repetitions:byte):real;
begin
  if Repetitions=1 then 
     Result:=1 
  else 
     Result:=EF;
end;

Extended HTML encoding for embedding Unicode in XML:

function HTMLEncode(WS:WideString):string; 
var n:integer; ch:WideChar; w:word; s:string;
begin 
  Result:='';
  for n:=1 to length(WS) do begin
       ch:=WS[n];
       w:=word(ch);
       if w>127 then begin 
          s:=IntToStr(w);
          s:='&#'+s+';';
          end
       else s:=ch;
   Result:=Result+s;
   end;
end;