A Gentle Introduction to xml

Batches

Batches

A batch consists of a number of debits followed by a number of credits.

• There must be at least one debit.
• There must be at least one credit.
• If there is more than one debit there must be exactly one credit.
• If there is more than one credit there can only be one debit.

Change the DTD so that the XML on the left passes validation but the XML on the right fails validation. The DTD given is too permissive - it allows any combination of card and cash.

<batch>
  <debit/>
  <credit/>
</batch>

<batch>
  <debit/>
  <debit/>
  <credit/>
  <credit/>
</batch>

<batch>
  <debit/>
  <debit/>
  <credit/>
</batch>

<batch>
</batch>

<batch>
  <debit/>
  <credit/>
  <credit/>
</batch>

<batch>
  <credit/>
  <debit/>
</batch>